PELAJARAN 2

THERMAL EQUILIBRIUM

Initially there is more heat transferred from hot to cold object compare from cold to hot

There is net flow of heat from hot object to cold object

Temperature of the hot object decrease and temperature of the cold object increase

After sometime the amount of heat transferred from A to B and B to A is the same

Net flow of heat become zero

Both objects has the same temperature

Thermal equilibrium is achievedBasic principle to construct a thermometer.

Two important principles to construct a thermometer are.

1Specific thermometric property i.e. a physical quantity which varies with temperature.

ThermometerThermometric property

Mercury thermometerVolume of mercury varies with temperature

2Calibration of thermometer i.e the process of marking-up a scale on a thermometer.

To produce a scale for a thermometer, two fixed points of thermometer must first be selected.

a) Lower fixed point (0oC) is the melting temperature of pure ice at standard atmospheric pressure.

b) Upper fixed point (100 o C) is the temperature of steam a standard atmospheric pressure.

The formula is used to calibrate a thermometer ( = temperature of a substance

(o= ice point

(100= steam point

xo = the length of the mercury column at ice point x100 = the length of the mercury column at steam point

x = the length of the mercury column when the thermometer is placed in a substance

Example 1

The lengths of the mercury column in a thermometer at the ice point and the steam point are 12 cm and 20 cm respectively. When the thermometer is placed in a liquid, the length of the mercury column is 15 cm. What is the temperature of the liquid?

Example 2

The lengths of the mercury thread in a thermometer are 4.0 cm and 24.0 cm respectively at 0oC and 100oC. What is the length of the thread when the thermometer is placed in a substance at 65 oC.

Mercury Thermometer

The specific thermometric property in used in this thermometer the changes of the volumes of mercury with the temperature i.e when the temperature increases ,the volume of the mercury increases.

The sensitivity of the thermometer can be increased by

1 using a thinner-walled glass bulb

2 reducing the diameter of the capillary tube

3 smaller bulb

Mercury is used in the thermometer because

1has a higher boiling point

2does not stick to the glass

3is opaque and therefore it is easier to read.

4expands and contracts uniformly

SPECIFIC HEAT CAPACITY, c The specific heat capacity of a material is defined as the amount of heat required to raise the temperature of 1 kg of the substance through a temperature of 1oC.

The S.I. unit for c is J kg-1 oC-1 A substance with a small specific heat capacity become hot and cold easily. A substance with a high specific heat capacity difficult to become hot and cold.

The relationship between m,c, ( and Q

Where,

Q = the heat energy transferred to the substancem = the mass of the substancec = the specific heat capacity of the substance ( = the temperature change

1) A metal of mass 2 kg. Calculate the amount of heat that must be transferred to the metal to raise the temperature from 30oC to 70oC. (specific capacity of the metal = 500 J kg -1 o C-1 )2) 8.4 x 10 5 J of heat energy raises the temperature of 4 kg of water from 40oC to 90oC. What is the specific heat capacity of the water?3) 0.2 kg of water at 100oC is mixed 0.25 kg of water at 10oC. What is the maximum temperature reached by the mixture?

4) A 2 kW, 240 V electric heater is used to raise the temperature of 3 kg of water. If power is supplied for 8 minutes, what is the increase in temperature of the water? (The specific heat capacity of water is 4200 J kg -1 o C-1)

5) The blocks P and Q in Figure 1 have the same mass. They are immersed in boiling water for a long time. P and Q are then transferred into beakers X and Y respectively as shown in Figure 2. The mass of water in both beakers X and Y is 0.25 kg and the initial temperature of the water in each beaker is the same.

Figure 1

Figure 2

Specific heat capacity of P is 900 J kg-1 o C-1Specific heat capacity of Q is 390 J kg-1 o C-1Specific heat capacity of water is 4 200 J kg-1 o C-1(a)(i)State the initial temperature of the blocks.

...

(ii)Why is the final temperature of the water in beaker X higher than that in beaker Y?

...

(b)(i) Calculate the rise in temperature of water in beaker Y if block Q release 8 400 J of heat energy.

(ii)State one assumption which you have made in b(i).

......6.Diagram 8.1 shows a 500W electric heater being used to heat a beaker of water on a compression balance.

(a) State the energy change involved when using the heater to heat the water.

..............................................................[ 1 mark ]

(b) The mass of water is 0.5 kg and the specific heat capacity of water is 4200 J kg- C-. The initial temperature of the water is 30 C. Calculate the energy absorbed by the water to reach its boiling point.

[ 2 marks ]

(c) When the water is boiling, the reading of the compression balance decreases by 0.0125 kg in 60 s. Calculate the specific latent heat of vaporization of the water.

[ 2 marks ] (d) Q, R and S are three different hot plates. These hot plates are used to heat roti canai. Table 8 shows the characteristics of each plate.

Hot Plates

Specific Heat Capacity,cJ kg-C-Mass, mkgPower, PW

Q3903.0600

R9002.51200

S4004.0900

The initial temperature of each plate is 30 C. The plates are ready to use when their temperature reaches 200C. Calculate the time taken to reach 200C for each plate.

(i) Plate Q

(ii) Plate R

(iii) Plate S

[5 marks](e) (i) Based on the answer in 8(d), Which plate is the most suitable for heating roti canai ?

...................................................................[ 1 mark ]

(ii) State one reason for the answer in 8(e)(i)

...................................................................[ 1 mark ]7. Table 8 shows two types of pot and their characteristics.

Table 8(a) What is the meaning of specific heat capacity?

...[1 mark] (b) Based on Table 8, state suitable characteristics of the pot if it is to be used for cooking something rapidly. Give reason for the suitability of the characteristics. (i) Material for making the pot.

.

Reason .... [2 marks]

(ii) Material for making the handle of the pot

..

Reason

.. [2 marks]

(iii) Mass of the pot

..

Reason

. [2 marks]

(c) The pots are heated by using an electric hot plate of power 800 W. Based on the information in the Table 8, calculate the time taken to achieve a temperature rise of 90oC for: (i) The clay pot

[2 marks]

(ii) The copper pot

[2 marks]

(d) Determine the most suitable pot that is safest to handle and can be heated in the shortest period of time. . [1 mark]8. Diagram 8 shows 2 models of frying pan.

(a) What is meant by specific heat capacity?

...[1 mark]

(b) Based on the information in Diagram 8, state the suitable characteristics of the frying pan that is used to cook food faster.

(i) Type of surface

...[1 mark]

Reason

..,,...[1 mark]

(ii) Specific heat capacity

,,..[1 mark]

Reason

..,,....[1 mark]

(c) Based on the answer in 8(b), determine which model in Diagram 8 will absorb heat effectively. Give reason for your choice.

..,,...

...[2 marks]

(d) A kettle contained 0.5 kg of water. The average heat absorb by the water is 16 Js-1 in 25 minutes. Calculate:

(i) The amount of heat absorbed by the water.

[1 mark]

(ii) The increase in temperature of water. [Specific heat capacity = 42 000 J kg-10C-1]

[2 marks]8. Diagram 3.1 shows a metal block P of mass 300 g at initial temperature 100 is immersed into the water at room temperature. Diagram 3.2 shows the graph of temperature against time of block P until it achieve thermal equilibrium.

(a) What is meant by thermal equilibrium?

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

(b) What is the temperature of block P when it is in thermal equilibrium?

.................................................................................[1 mark]

(c) Explain how block P achieve thermal equilibrium.

............................................................................................... .................................................................................[2 mark]

(d) Calculate the amount of heat lost by block P when its achieved thermal equilibrium. [Specific heat capacity of block P = 900 J kg-1 oC-1 ][2 mark]9. Diagram 7.1 shows a cooling pad used to lower the temperature of a person having fever. The pad consists of a gel and is cooled in a refrigerator before it is placed on the forehead of the person to remove the heat.

(a) (i) What is meant by heat?

......................................................................[1 mark]

(ii) Explain how the heat is removed from the forehead of

the person

.............................................................................................................................................................[2 marks]

(b) The mass of the gel in the pad is 0.03 kg and its specific heat capacity is 4300 J kg-1 C-1. The initial temperature of the pad is 15 C and the final temperature is 36 C. Calculate the amount of heat removed by the pad.

[2 marks]

(c) It is suggested that the cooling pad should be modified so that it can remove more heat. Give two suggestion and the reasons for doing so.

Suggestion 1:

.................................................................................[1 mark]

Reason:

.................................................................................[1 mark]

Suggestion 2:

.................................................................................[1 mark]

Reason:

................................................................................[1 mark] 10) The following table shows the characteristics of materials which could be used to make the food container to keep the food warm. You are asked to investigate the characteristics of the materials in the table which could be used to make the food container as in the figure above. Explain the suitability of each characteristic in the table and hence, determine which material is most suitable to be used to make the food container. Justify your choice.Charateristic

MaterialDensity/

kg m-3

Melting

point / CSpecific heat

capacity/J kg-1 oC-1Thermal

conductivity

P2 710

660910High

Q910271 600Low

R1 0502401 300

Low

S2 6001 200670

Low

T3 8002 020800

High

11. Diagram 11.2 shows a thermos flask used to maintain the temperature of hot drink for a long time.

Table 11.1 shows the characteristics of four different thermos flasks.

Thermos FlaskStopperSpace PDouble Walled tube

Made ofCoated by

WHollow plasticVacuumGlassShiny paint

XHollow plasticvacuumCopperBlack Paint

YSolid plasticAir GlassBlack paint

ZSolid plasticAirCopperShiny paint

Explain the suitability of each characteristics of the thermos flask and determine the most suitable thermos flask. Give your reason.

12) Diagram 11.2 shows an ice cream container used by an ice cream seller using his motorcycle. Table 11.3 shows the specification of four types of ice cream containers P, Q, R and S, that can be used by an ice cream seller to carry ice cream. You are required to determine the most suitable ice cream container to carry ice cream.

Study the specification of the four types of ice cream container based on the following aspects:

- Specific heat capacity of ice cream box

- Size of ice cream box

- Material of outer box

- Colour of outer box

Explain the suitability of the aspects [10 marks]13) The figure below shows a cooling system of car.

You are asked to modify the the cooling system so that it can cool the car better. Your modification should include the following aspects:

i) specific heat capacity of the coolant

ii) boiling point of the coolant

iii) density of the coolant

iv) size of the radiator fan

v) number of fin blade14. Diagram below shows a simple solar waterheating system. Energy from the Sun falls on the solar panel. Water is pumped around the system so that a store of hot water is made available in the tank.

Using suitable physics concepts, explain the required modification needed in designing an efficient solar

water-heating system. The modification should include the following aspects:

(i) pipes design

(ii) material used for the pipe(iii) heat absorption

(iv)position of the tankLATENT HEATThe specific latent heat of fusion :

Is the quantity heat of energy required to change 1 kg of a substance from the solid state to the liquid state, without a change in temperature.

The specific latent heat of Vaporisation :

Is the quantity heat of energy required to change 1 kg of a substance from the liquid state to the gaseous state, without a change in temperature. The S.I. unit of is J kg-1

Q = the heat energy to change state of matterm = the mass of the substance

l = the specific latent heat of the substance

1) What is the quantity of heat required to melt 2.0 kg ice at 0 o C.(The specific latent heat of fusion of ice = 3.34 x 105 J kg-1)

2) How much energy needed to melt 4.0 kg of ice to water at 20 o C. (The specific heat capacity of water = 4.2 x 103 J kg-1 o C-1.The specific latent heat of fusion of ice = 3.34 x 105 J kg-1)

3) A 800 W electric heater is used to boil water. What is the time required to reduce the mass of water by 4 kg after the water has reached its boiling point?[ Specific latent heat of vaporization of water = 2.26 x 106 J kg -1 ]

4) 0.5 kg of a solid is heated by a 100 W heater. The graph shows how the temperature substance varies with time.

Based on the graph above calculate the specific latent heat of fusion of the solid and specific heat capacity of solid .

5 A solid substance of mass 0.1 kg is heated using 200 W heater. A graph showing in variation of temperature with time is shown in Figure below.

(a)Based on the graph , what are the states of matter between point

(i)WX

(ii)XY.

(iii)YZ.

(b)Using kinetic theory of matter, explain why

(i)at section XY , the temperature is remains constant?

..

(ii)at section YZ the temperature increases

(c)Using the graph, determine

(i) the melting point of the substance?

(ii) the specific latent heat of fusion of the substance.

.

6. The below shows two set of apparatus to determine the specific latent heat of fusion of ice. Set A is not connected while set B is connected to the power supply.

Set A

(a) What is the function of set A?

..............................................................................[1 mark]

(b) Compare the thermometer readings for set A and set B after 5 minutes. What can you say about the readings?

..............................................................................[1 mark]

(c) Name the heat involved in the processes.

..............................................................................[1 mark]

(d) (i) What is the amount of water collected in the beaker in set A after 5 minutes.

.....................................................................[1 mark]

(ii) What is the amount of water collected in the beaker in set B after 5 minutes.

......................................................................[1 mark]

(iii) Determine the amount of water collected due to the heat from the heater only.

.....................................................................[1 mark]

(iv) If the power of the heater used is 200 W, calculate the specific latent heat of fusion of ice.

[2 mark]7. Fig. 3.1 shows apparatus to measure the specific latent heat of fusion of water. In this question, you may ignore heat transfer to the ice from the room. The heater is switched on and water drips into the beaker at a constant rate. In 2.0 minutes, 31 g of water drips into the beaker. The power of the heater is 85 W.

(a) Calculate the amount of electrical energy supplied to the heater in 2.0 minutes.

[2]

(b) Use your answer to (a) to calculate the specific latent heat of fusion of water.

[2]

(c) In another experiment using the same heater, ice colder than 0 C is used. State why less water drips into the beaker in 2.0 minutes.

................................................................................... [1]7. Diagram 3.1 shows the change of phase when 1 kg of ice is converted into steam. Q1, Q2and Q3 are the heat energies absorbed during the heating process.

(a) Name the heat energy, Q1, which is absorbed from R to S. .......................................................................[1 mark]

(b) State one reason why the temperature at R and S is the same even though heat is supplied.

.....................................................................[1 mark]

(c) Calculate the heat energy Q2 which is absorbed from S to T. [Specific heat capacity of water is 4200 Jkg-1C-1][ 2 marks]8 Diagram 7.1 shows two cups of coffee of equal mass being cooled by adding a few pieces of ice cubes.

Cup A

Cup B DIAGRAM 7.1

Initially, each cup contains 0.2 kg of coffee at 75.5 oC. It is observed that both cups of coffee reach a final temperature of 25 oC at the same time.

(a)The melting of ice involves the absorption of latent heat of fusion. What is meant by specific latent heat of fusion?

... [1 mark](b)(i) Which cup of coffee requires more ice?

... [1 mark]

(ii)Explain your answer in (b)(i).

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

[2 marks]

(c) Calculate the heat released when the coffee is cooled down to 25 oC.[Specific heat capacity of coffee = 4500 J kg1 oC1]

[2 marks]

(d)(i)Calculate the mass of ice needed to cool the coffee in cup A to 25 oC.[Specific heat capacity of water = 4200 J kg1oC1, specific latent heat of fusion of ice = 3.36 x 105 J kg1]

[3 marks]

(ii)State one assumption which you made in your calculation in (d)(i).

.... [1 mark]Boyles Law

Boyles law states that For a fixed mass at constant temperature, the pressure of gas is inversely proportional to its volume

1) A 5 cm3 balloon is filled by a gas at a pressure of 1 x 105 Pa When the balloon is filled by 20 cm3 of the gas, what is the new pressure of the gas?2) An air bubble has a volume 2.0 cm3 at a depth 40m in the sea. What is the volume of the air bubble when it reaches the surface of the sea water. [Assume the atmospheric pressure is equivalent to 10 m of water ]

3. A rod of tube with one end closed has a strip of mercury 3 cm long. When the tube is held vertically, the length of air trapped is 8 cm as in figure (a) above. Atmospheric pressure is taken as 76 cm Hg.

(a) Calculate the length, x of air which is trapped when the tube is placed horizontally as in figure (b) above.

(b) Calculate the length, y of air which is trapped when the tube is inverted as shown in figure (c) above.4. Diagram 5.1 and 5.2 show instrument K being used to measure pressure for a fixed mass of gas in an air

container.

(a) Name the instrument K.

.. [1 mark] (b) Based on the observation of Diagram 5.1 and 5.2,

(i) Compare the volume of the gas

.. [1 mark] (ii) Compare the pressure of the gas

.. [1 mark] (iii) State the assumption made while performing the experiment.

.. [1 mark] (c) Using your answers in (b)(i) and (b)(ii), sketch the graph of

pressure against volume of the gas

(d) Name the physics law which is involved in the above

observation.

.... [1 mark] (e) Using the kinetic theory of matter, explain why pressure changes when the gas volume changes.

..............................................................................................................................................................................[2 marks]The Pressure LawThe pressure law states that For a fixed mass at constant volume, the pressure of gas is directly proportional to its absolute temperature

5) A cylinder of oxygen at 27o C has a gas pressure at 3 x 106 Pa. What is the temperature of the oxygen if the cylinder is cooled and the new pressure of the gas is 2.73 x 106 Pa.

6. Diagram 7 shows a tyre of a car that is going to be used to travel from Kuala Lumpur to Kuala Terengganu.

(a) After the long journey, (i) what happen to the temperature of the air in the tyre

......................................................................[1 mark]

(ii) state one other physical quantity that will also change.

.........................................................................[1 mark]

(b) Based on the answers in (a) (i) and (a) (ii), name the gas law involve.

............................................................................[1mark]

(c) Before a long journey, the driver checked the air pressure of his car tyres. The air pressure of the tyres was 200 kPa at a temperature 27C. After the journey, the air pressure of the tyres increase to 230 k Pa. What is the temperature of the air in the tyre after the journey? [Assume the volume of the tyre is constant]

[3 marks]

(d) The tyre in Diagram 7 is not suitable to be used on a muddy road. Suggest modifications to be done based on the characteristics given.

(i) Surface area of the tyre

..............................................................................[1 mark]

(ii) Reason

..............................................................................[1 mark] (iii) The track of the tyre

..............................................................................[1 mark]

(iv) Reason

..............................................................................[1 mark]Charles Law

Charless law states that For a fixed mass at constant pressure, the volume of gas is directly proportional to its absolute temperature

7) A sample of gas has a volume 100 cm3 at 20o C. To what temperature would you have to heat if you wanted to double the volume to 200 cm3. 8 Figure 1 shows a balloon is tightly fastened to the open end of a test tube mouth of a balloon before and after the test tube is heated. Figure 2 shows air is trapped inside a capillary tube by a bead of sulfuric acid before and after the capillary tube is heated.

(a)

(b)

Figure 1

(a)

(b)

Figure 2 (a)(i) Observe Figure 1 and Figure 2 and state one similarity between the volume of air in the balloon and the capillary tube ...

(ii)Compare the mass of air in Figure 1(a) and Figure 1(b).

....................................(b) (i)Based on the observation in (a)(i)and the comparison in (a)(ii), give a relationship between the physical quantities involved.

...

(ii)Name the law involved in b(i)

...

(iii)Based on the the kinetic theory of gases explain how the law in b(i) is occurred.

120

Ice / Ais

Q = m l

100

Q = m c (

Ice / Ais

7

P1 V1 = P2 V2

P1 = P2

T1 T2

80

V1 = V2

T1 T2

60

20

0

EMBED PBrush

40

40

50

60

70

80

90

100

water

P

time / s

Temperature / oC

I kg ice at 0C

I kg water at 0C

I kg water at 100C

I kg steam at 100C

PAGE 6