Maltby Academy 1

1. The reaction between sulphur dioxide and oxygen is a dynamic equilibrium.

2SO2 + O2 2SO3 H = –196 kJmol–1

(a) Explain what is meant by dynamic equilibrium.

..................................................................................................................................

..................................................................................................................................

.................................................................................................................................. (2)

(b) In the table below state the effect on this reaction of increasing the temperature and of

increasing the pressure.

Effect on the rate of the

reaction

Effect on the position of

equilibrium

Increasing the

temperature

Increases

Increasing the pressure

(3)

(c) This reaction is one of the steps in the industrial production of sulphuric acid. The

normal operating conditions are a temperature of 450 °C, a pressure of 2 atmospheres

and the use of a catalyst.

Justify the use of these conditions.

(i) A temperature of 450 °C:

......................................................................................................................

......................................................................................................................

...................................................................................................................... (3)

Maltby Academy 2

(ii) A pressure of 2 atmospheres:

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(iii) A catalyst:

......................................................................................................................

......................................................................................................................

...................................................................................................................... (1)

(d) Give the name of the catalyst used.

.................................................................................................................................. (1)

(e) Give one large scale use of sulphuric acid.

.................................................................................................................................. (1)

(Total 13 marks)

2. In the vapour phase sulphur trioxide dissociates:

2SO3(g) 2SO2(g) + O2(g)

(a) (i) Write an expression for Kp for this dissociation.

(1)

Maltby Academy 3

(ii) At a particular temperature, 75% of the sulphur trioxide is dissociated, producing a

pressure of 10 atm. Calculate the value of Kp at this temperature paying, attention

to its units.

(5)

(b) Solid vanadium(V) oxide, V2O5, is an effective catalyst for this reaction. State the effect

of using double the mass of catalyst on:

(i) the position of the equilibrium;

............................................................................................................................

............................................................................................................................ (1)

(ii) the value of Kp.

............................................................................................................................

............................................................................................................................ (1)

(Total 8 marks)

Maltby Academy 4

3. Consider the following equation:

2SO2 + O2 2SO3

2.0 moles of SO2 and 1.0 mole of O2 were allowed to react in a vessel of volume 60 dm3.

At equilibrium 1.8 moles of SO3 had formed and the pressure in the flask was 2 atm.

(a) (i) Write the expression for Kc for this reaction between SO2 and O2.

(1)

(ii) Calculate the value of Kc, with units.

(3)

(b) The reaction between SO2 and O2 is exothermic. State the effect on the following, if the

experiment is repeated at a higher temperature:

(i) Kc ……………………………………………………………………………..

(1)

(ii) the equilibrium position .................................................................................... (1)

(c) State the effect of a catalyst on:

(i) Kc ……………………………………………………………………………..

(1)

Maltby Academy 5

(ii) the equilibrium position .................................................................................... (1)

(d) (i) Write the expression for Kp for the reaction between SO2 and O2.

(1)

(ii) Calculate the mole fractions of SO2, O2 and SO3 at equilibrium.

(2)

(iii) Calculate the partial pressures of SO2, O2 and SO3 at equilibrium.

(1)

(iv) Calculate the value of Kp, with units.

(2)

(Total 14 marks)

Maltby Academy 6

4. The equation below shows a possible reaction for producing methanol.

CO(g) + 2H2(g) CH3OH(l) ΔHο = 129 kJ mol

–1

(a) The entropy of one mole of each substance in the equation, measured at 298 K, is shown

below.

Substance

Sο

/J mol1

K1

CO(g) 197.6

H2(g) 130.6

CH3OH(l) 239.7

(i) Suggest why methanol has the highest entropy value of the three substances.

.............................................................................................................................

............................................................................................................................. (1)

(ii) Calculate the entropy change of the system, ΔSοsystem, for this reaction.

(2)

(iii) Is the sign of ΔSοsystem as expected? Give a reason for your answer.

.............................................................................................................................

.............................................................................................................................

............................................................................................................................. (1)

Maltby Academy 7

(iv) Calculate the entropy change of the surroundings ΔSοsurroundings, at 298 K.

(2)

(v) Show, by calculation, whether it is possible for this reaction to occur spontaneously

at 298 K.

(2)

(b) When methanol is produced in industry, this reaction is carried out at 400 ºC and 200

atmospheres pressure, in the presence of a catalyst of chromium oxide mixed with zinc

oxide. Under these conditions methanol vapour forms and the reaction reaches

equilibrium. Assume that the reaction is still exothermic under these conditions.

CO(g) + 2H2(g) CH3OH(g)

(i) Suggest reasons for the choice of temperature and pressure.

Temperature ........................................................................................................

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

Pressure ...............................................................................................................

.............................................................................................................................

............................................................................................................................. (3)

Maltby Academy 8

(ii) The catalyst used in this reaction is heterogeneous. Explain this term.

.............................................................................................................................

............................................................................................................................. (1)

(iii) Write an expression for the equilibrium constant in terms of pressure, Kp, for this

reaction.

CO(g) + 2H2(g) CH3OH(g)

(1)

(iv) In the equilibrium mixture at 200 atmospheres pressure, the partial pressure of

carbon monoxide is 55 atmospheres and the partial pressure of hydrogen is 20

atmospheres.

Calculate the partial pressure of methanol in the mixture and hence the value of the

equilibrium constant, Kp. Include a unit in your answer.

(2)

Maltby Academy 9

(c) The diagram below shows the distribution of energy in a sample of gas molecules in a

reaction when no catalyst is present. The activation energy for the reaction is EA.

(i) What does the shaded area on the graph represent?

............................................................................................................................. (1)

(ii) Draw a line on the graph, labelled EC, to show the activation energy of the

catalysed reaction. (1)

(Total 17 marks)

5. The reaction between nitrogen and hydrogen can be used to produce ammonia.

N2(g) + 3H2(g) 2NH3(g) ΔH

ο = – 92.2 kJ mol

–1

Standard entropies are given below

Sο [N2(g)] = +191.6 J mol

–1 K

–1

Sο [H2(g)] = +130.6 J mol

–1 K

–1

Sο [NH3(g)] = +192.3 J mol

–1 K

–1

Maltby Academy 10

(a) Calculate the entropy change of the system, ΔSοsystem, for this reaction. Include a sign and

units in your answer.

(2)

(b) Calculate the entropy change of the surroundings, ΔSοsurroundings, at 298 K. Include a sign

and units in your answer.

(2)

(c) (i) Calculate the total entropy change, ΔSοtotal, at 298 K. Include a sign and units in

your answer.

(1)

Maltby Academy 11

(ii) Is this reaction feasible at 298 K? Justify your answer.

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(d) In industry the reaction is carried out at about 700 K using an iron catalyst and high

pressures.

(i) The yield of ammonia produced at equilibrium is less at 700 K than at 298 K, if the

pressure remains constant. In terms of entropy, explain why this happens.

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(ii) Higher pressures increase the yield of ammonia at equilibrium. Suggest a reason

why pressures greater than 300 atmospheres are not routinely used.

...............................................................................................................................

...............................................................................................................................

...............................................................................................................................

............................................................................................................................... (1)

(iii) Iron is a heterogeneous catalyst. Explain what is meant by heterogeneous.

...............................................................................................................................

............................................................................................................................... (1)

(Total 9 marks)

Maltby Academy 12

6. (a) Define the term standard enthalpy of formation.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (3)

(b) In the Haber process, ammonia is manufactured from nitrogen and hydrogen as shown in

the equation.

N2(g) + 3H2(g) 2NH3(g)

(i) Use the bond enthalpies below to calculate the standard enthalpy of formation of

ammonia.

Bond Bond enthalpy / kJ mol–1

N≡N in N2 +945

H–H in H2 +436

N–H in NH3 +391

(4)

Maltby Academy 13

(ii) Draw a labelled enthalpy level diagram for the formation of ammonia in the Haber

process.

Enthalpy

(2)

(iii) State the temperature used in the Haber process and explain in terms of the rate of

reaction and position of equilibrium, why this temperature is chosen.

Temperature .......................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (3)

Maltby Academy 14

(iv) Identify the catalyst used in the Haber process and state what effect, if any, it has

on the equilibrium yield of ammonia.

Catalyst ................................................................

Effect on yield ................................................................................................... (2)

(v) Explain why it is necessary to use a catalyst in this process.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (1)

(c) The pressure used in the Haber process is 250 atmospheres.

(i) State and explain an advantage of increasing the pressure to 1000 atmospheres.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (2)

(ii) Suggest a disadvantage of using a pressure of 1000 atmospheres.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (1)

(Total 18 marks)

Maltby Academy 15

7. One stage in the manufacture of sulphuric acid is

2SO2(g) + O2(g) 2SO3(g)

The equilibrium constant Kp =

22

3

O2SO

2SO

pp

p

(a) 10.0 mol of SO2 and 5.00 mol of O2 were allowed to react. At equilibrium, 90.0% of the

SO2 was converted into SO3.

(i) Calculate the number of moles of SO2, O2 and SO3 present in the equilibrium

mixture.

(2)

(ii) Calculate the mole fractions of SO2, O2 and SO3 at equilibrium.

(1)

Maltby Academy 16

(iii) Assuming that the total pressure of the equilibrium mixture was 2.00 atm, calculate

the partial pressures of SO2, O2 and SO3 at equilibrium.

(1)

(iv) Calculate the value of Kp.

(2)

(b) The reaction between sulphur dioxide and oxygen is exothermic.

(i) State the effect, if any, on Kp of increasing the temperature at constant pressure.

........................................................................................................................... (1)

Maltby Academy 17

(ii) Use your answer to (i), and the expression Kp =

22

3

O2SO

2SO

pp

p

to explain the effect

on the position of equilibrium of increasing the temperature at constant pressure.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (2)

(c) The reaction was repeated at a higher pressure whilst maintaining a constant temperature.

(i) State the effect, if any, of an increase in the total pressure on the value of Kp.

............................................................................... (1)

(ii) State the effect, if any, of this increase in pressure on the amount of sulphur

trioxide in the equilibrium mixture.

............................................................................... (1)

(d) State the effect, if any, of a catalyst on:

(i) Kp

............................................................................... (1)

(ii) the equilibrium position.

............................................................................... (1)

(Total 13 marks)

Maltby Academy 18

8. Methanoic acid and ethanol react together to form ethyl methanoate, HCOOC2H5, and water.

This reaction is reversible and can be allowed to reach equilibrium.

HCOOH(l) + C2H5OH(l) HCOOC2H5 (l) + H2O(l) ΔH = +45 kJ mol–1

(a) Draw the full structural formula of ethyl methanoate, showing all bonds.

(1)

(b) What type of organic compound is ethyl methanoate?

..................................................................................................................................... (1)

(c) In an experiment, 3.00 mol methanoic acid, HCOOH, and 6.25 mol ethanol, C2H5OH,

were mixed together. A small quantity of catalyst was added. The mixture was left for

several days in a water bath to reach equilibrium at constant temperature.

(i) Complete the table.

Number of moles in the reaction mixture

HCOOH C2H5OH HCOOC2H5 H2O

at start of

experiment 3.00 6.25 0.00 0.00

at equilibrium 0.50

(2)

Maltby Academy 19

(ii) Write an expression for the equilibrium constant, Kc, for the reaction.

(1)

(iii) Calculate Kc for the reaction at the temperature of the experiment. The total volume

of the equilibrium mixture was 485 cm3.

(2)

(iv) State and explain whether Kc for this reaction has units.

...........................................................................................................................

........................................................................................................................... (1)

Maltby Academy 20

(d) (i) The temperature of this equilibrium mixture is lowered.

Explain the effect of this on the value of the equilibrium constant and hence on the

yield of ethyl methanoate.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (4)

(ii) A student added more catalyst to the mixture.

State, giving a reason, what would happen to the composition of the equilibrium

mixture.

...........................................................................................................................

........................................................................................................................... (1)

(Total 13 marks)

9. (a) Still reacting / rate of forward reaction and backward reaction equal / implication that

forward and backward reactions are still taking place (1)

But concentrations constant / no macroscopic changes (1) 2

(b) Temp (Increases) Left / to SO2 / to endothermic / lower yield (1)

Press Increases/faster (1) Right to SO3 / to smaller number of molecules (1)

3

Maltby Academy 21

(c) (i) Increases rate / or suitable comment on rate (1)

Moves position of equilibrium to endothermic side / or suitable comment on

equilibrium such as reasonable yield / less SO3 (1)

Either compromise in which the rate is more important than the position of

equilibrium

or optimum temperature for catalyst to operate

or valid economic argument (1) 3

(ii) Increases rate / more SO3 / only needs small pressure to ensure gas passes

through plant / high or reasonable yield obtained at 1 atms or at low pressure

anyway (1)

and references to economic cost against yield benefit

e.g increase in pressure would increase yield of product but the increase in yield

would not offset the cost of increasing the pressure (1) 2

(iii) Catalyst speeds up reaction (1) 1

(d) Vanadium (V) oxide / vanadium pentoxide / V2O5 (1) 1

(e) Any one use

production of fertilizers, detergents, dyes, paints, pharmaceuticals (in) car batteries,

pickling metal 1 [13]

10. (a) (i) Kp = 2

SO3

O2

2

SO2

P

PP (1)

[ ] no mark

( ) OK 1

(ii) 2SO3 2SO2 + O2

Mols at start 2 0 0

mols at equ 0.5 1.5 0.75 (1)

Mark by process

1 mark for working out mole fraction

1 mark for × 10

1 mark for correct substitution in Kp and answer

1 mark for unit

Maltby Academy 22

i.e. PSO2 = 75.2

5.1 × 10 = 5.46

PO2 = 75.2

7.0 × 10 = 2.73

PSO3= 75.2

5.0 × 10 = 1.83

n.b. could show mole fraction for all 3 and then × 10 later to

give partial pressure.

Kp = (5.46)2 × (2.73) / (1.83)

2 = 24.5 (1) atm (1) 5

(b) (i) No effect (1) 1

(ii) No effect (1) 1 [8]

11. (a) (i) Kc = [SO3]2 / [SO2]

2 [O2] (1) 1

(ii) 30

2.0

60

1.0

60

8.1

= 3.33 103

1.67 10–3

0.03 (1)

Kc = 323

2

1067.1)1033.3(

)03.0(

= 4860or 4.86 104

(1)

mol1

dm3 (1) 3

(b) (i) Kc decreases (1) 1

(ii) shifts to left / in reverse (1) 1

(c) (i) no effect (1) 1

(ii) no effect (1) 1

(d) (i) Kp = pSO32 / pSO2

2 pO2 (1) penalise square brackets 1

(ii) Total number of moles (1) consequential on a (ii)

SO2 = 0.0952(4); O2 = 0.0476 (2); SO3 = 0.857 (1) (1) 2

Maltby Academy 23

(iii) Partial pressures: SO2 = 0. 190 (5) atm; O2 = 0.0952 (4) atm; 1

SO3 = 1.71(4) atm (1) i.e. multiply answer in (ii) by 2

(iv) 1.7142 / 0.1905

2 0.09524 = 850 (1)

atm1

(1) 2 [14]

12. (a) (i) Methanol is the biggest/ most complex molecule / greatest MR /most

atoms/most electrons 1

(ii) Ssystem = 239.7 – 197.6 – 2(130.6)

= –219.1/ –219 J mol–l

K–1

Method (1)

answer + units (1) 2

(iii) yes as 3 molecules 1 OR yes as (2) gases a liquid 1

(iv) Ssurr = –H/T (stated or used) (1)

= –(–129/ 298) = +0.433 kJ mol–1

K–1

/ +433 J mol–1

K–1

/+ 432.9 (1)

–1 for wrong units/ no units / more than 4 SF

–1 for wrong sign/ no sign 2

(v) Stotal = –219.1 + 433 = +213.9 / +213.8 J mol–1

K–1

/ +214 J mol–1

K–1

/

+0.214 kJ mol –1

K–1

(1)

Positive so possible (1) 2

(b) (i) Temperature

Faster at 400°C (1)

even though yield is lower (1)

Pressure

Higher pressure improves yield of methanol (1)

Higher pressure increases rate (1)

Maximum 3 3

(ii) Not in same phase as reactants. ALLOW state instead of phase 1

(iii) Kp = p(CH3OH)/p(CO)×p(H2)2 1

(iv) Partial pressure of methanol = 200 – 55 – 20 = 125 atm (1)

Kp = (125)/55×202

= 5.68 × 10–3

/ 5.7 × 10–3

atm–2

(1) 2

(c) (i) Number of molecules / fraction of molecules with energy EA /number

of molecules which have enough energy to react. 1

(ii) Vertical line / mark on axis to show value to the left of line EA 1

[17]

Maltby Academy 24

13. Penalise units only once in this question

(a) (2×192.3)–[191.6 + (130.6 × 3)] (1)

= –198.8/199 J mol–1

K –1

(1) 2

(b) 298

/2.92––

298

/10002.92–– –H / T (1)

= + 309(.4) J mol–1

K–1

/ + 0.309(4) kJ mol–1

K–1

(1) 2

(c) (i) –198.8 + 309 = + 110 J mol–1

K–1

(3 SF)

OR

– 198.8 + 309.4 = + 111 J mol–1

K–1

(3 SF)

[Do not penalise missing + sign if penalised already in (b)]

NOT 4SF. Penatise SF only once on paper 1

(ii) Yes, as Stotal is positive / total entropy change 1

(d) (i) Higher T makes Ssurroundings decrease (so Stotal is less positive) 1

(ii) Cost (of energy) to provide compression/ cost of equipment

to withstand high P/ maintenance costs.

NOT safety considerations alone 1

(iii) Different phase/state (to the reactants) 1 [9]

14. (a) Enthalpy/heat/energy change for one mole of a

compound/substance/ a product (1)

NOT solid/molecule/species/element

Reject “heat released or heat required” unless both mentioned

to be formed from its elements in their standard states (1)

ALLOW normal physical state if linked to standard conditions

Reject “natural state” / “most stable state”

standard conditions of 1 atm pressure and a stated temperature (298 K) (1) 3

Reject “room temperature and pressure”

Reject “under standard conditions”

Maltby Academy 25

(b) (i) Bonds broken Bonds made

N≡N (+)945 6N–H (–)2346 (1)

and

3H–H 2253)(

1308)(

(1)

∆H = 945 +1308 – 2346

= –93 sign and value (1)

∆Hο = –93 = –46.5 (kJ mol

–1)

sign and value q on 3rd

mark (1)

2 4

Accept –46.5 (kJ mol–1

) with working (4)

Accept + 46.5 with working max (3)

Accept +93 with working max (2)

(ii)

( )Enthalpy

N2 + (3)H2

(2)NH 3

H

OR

–93

Accept –46.5

Correct labelled levels (1)

Reject “Reactants” and “Products” as labels

∆H labelled (1)

direction of arrow must agree with thermicity

Accept double headed arrow

Diagram marks cq on sign and value of ∆H in (b)(i)

IGNORE activation energy humps 2

Maltby Academy 26

(iii) 350–500 °C (1)

Accept any temperature or range within this range

higher temperature gives higher rate (1)

but a lower yield because reaction is exothermic (1)

Accept favours endothermic reaction more than exothermic so

lower yield

OR

Lower temperature give higher yield because reaction is exothermic (1)

but rate is slower (1) 3

Accept cq on sign of ∆Hf in (b)(i) or levels in (ii)

Reject lower temp favours exothermic reaction

(iv) Iron / Fe (1) IGNORE any promoters

no effect on yield (1) 2

(v) temp would have to be much higher for a reasonable rate then

yield would be too low

“lower activation energy” implies reasonable rate

OR

Allows reaction at a lower temp at a reasonable/fast rate giving

a reasonable yield. 1

Accept rate too slow without catalyst at a temp giving a

reasonable yield

Reject to lower activation energy of reaction

(c) (i) advantage

higher (equilibrium) yield/more NH3 in equilibrium

mixture/equilibrium shifts to right (1)

because smaller number of (gaseous) moles/molecules on rhs (1)

IGNORE any reference to change in rate 2

Reject just “more ammonia”

Maltby Academy 27

(ii) disadvantage

(plant more) expensive because thicker pipes would be needed

OR

cost (of energy) for compressing the gases/cost of pump

OR

Cost of equipment/pressure not justified by higher yield 1

Accept stronger or withstand high pressure for thicker

Accept vessel/container/plant /equipment/reaction vessels for

pipes

Reject “just more expensive”

Reject “just thicker pipes etc”

Reject apparatus [18]

15. (a) IGNORE s.f. throughout this question

(i) moles SO2 (10.0 – 9.00) = 1.00 (mol)

moles O2 (5.00 – 4.50) = 0.500 (mol)

moles SO3 9.00 (mol)

all 3 correct → (2)

2 correct → (1) 2

Reject multiples of the stated moles

(ii) All three ÷ total number of moles (1)

i.e.

212or )0952.0(

5.10

00.12

SOX

211or )0476.0(

5.10

500.02

OX

76

2118 or or )857.0(

5.10

00.93

SOX

Reject rounding to 1 sig fig

Mark consequential on (a)(i) 1

Maltby Academy 28

(iii) All three × total pressure (1)

i.e.

pSO2 = 214or 00.2

5.10

00.1

= 0.190 (atm)

pO2 = 212or 00.2

5.10

500.0

= 0.0952 (atm)

pSO3 = 712

2136 or or 00.2

5.10

00.9

= 1.71 (atm)

Mark consequential on (a)(ii) 1

(iv) )0952.0()190.0(

)71.1(2

2

pK

Kp = 851 (1) atm–1

(1)

Mark consequential on (a)(iii) and (a)(iv) 2

Accept answer with units and no working (2)

Accept “correct answers” between 845 and 855 as this covers

rounding up etc

Reject wrong units e.g. mol–1

dm3

(b) (i) (Kp) decreases 1

(ii) (Kp decreases so)

Reject any Le Chatelier argument (this prevents access to 1st

mark)

fraction/quotient 22

2

32

pOSOp

SOp

has to decrease (to equal new kp) (1)

so shifts to left hand side (1) – this mark only

available if (b)(i) answer was kp decreases.

Reject shifts to right, even if answer to (b)(i) was kp increases

(as 3SOp decreases whereas

2SOp and 2Op increase) 2

(c) (i) No effect/none/zero (effect) 1

Maltby Academy 29

(ii) Increases

OR

more SO3/more sulphur trioxide

OR

increases amount of SO3/sulphur trioxide 1

(d) (i) No effect/none/zero (effect) 1

(ii) No effect/none/zero (effect) 1 [13]

16. (a)

H C

O

O C

H

H

C H

H

H 1

(b) ester 1

(c) (i) Moles: C2H5OH: 3.75 (1)

Moles: HCOOC2H5 : 2.50 and moles H2O : 2.50 (1) for both 2

(ii) OH]H[HCOOH][C

]OH][HHCOOC[

52

252cK 1

Reject obviously round brackets “( )”

Maltby Academy 30

(iii)

485.075.3

485.050.0

485.050.2

485.050.2

cK (1)

Must have clearly divided moles of each component by

0.485 for 1st mark e.g.

[HCOOC2H5] = [H2O] = 5.16 (mol dm–3

)

and [HCOOH] = 1.03 (mol dm–3

)

and [C2H5OH] = 7.73 (mol dm–3

)

= 3.33 (1) stand alone mark

IGNORE sig.figs. 2

Accept 3.750.50

(2.50)K

2

c

= 3.33 only scores (2) if it is stated

that V cancels either here or in (iv)

If [H2O] omitted in (ii), then answer

Kc = 0.647 mol–1

dm3

(2) but this will give

Kc = 1.33 mol–1

dm3 with V omitted from calculation (1)

Reject 1st mark if 485 used as V in expression

(iv) No, (as) equal numbers of moles on both sides

OR volumes cancel

OR mol dm–3

cancel

OR units cancel

OR crossing out units to show they cancel 1

Accept “equal powers/moles on both sides”

OR “powers cancel”

Mark CQ on Kc expression in (ii)

Reject “concentrations cancel”

(d) (i) (as reaction) endothermic (1)

Accept exothermic in backward direction (or words to that

effect)

Kc decreases (1)

If state exothermic in forward direction, 1 mark only (out of 4)

for CQ “increase in Kc”

numerator in quotient (has to) decrease

OR denominator in quotient (has to) increase

OR fraction (has to) decrease (1)

yield of HCOOC2H5 decreases (1) 4

Maltby Academy 31

(ii) no effect as catalysts do not affect (the value of) K

OR

no effect as catalysts do not affect the position of equilibrium

OR

no effect as catalysts do not affect the yield

OR

No effect as catalysts increase the rate of the forward and

backward reactions equally/to the same extent

OR

no effect as catalysts only increase the rate

OR

no effect as catalysts only alter the rate

“no effect” can be stated or implied

IGNORE any references to activation energy 1

Reject just “catalysts increase rate” [13]