do now 2nahco 3 + 85 kj na 2 co 3 + h 2 o + co 2 is this an endothermic or exothermic reaction?...
TRANSCRIPT
Do Now
2NaHCO3 + 85 kJ Na2CO3 + H2O + CO2
Is this an endothermic or exothermic reaction?
Calculate the amount of heat transferred when 36 g of NaHCO3 is decomposed.
Thermochemical Equations
Enthalpy (H)
• Heat content of a system at constant pressure
ΔHrxn = Hfinal – Hinitial
Changes of State
• Many processes other than chemical reactions absorb or release heat
Changes of StateΔHvap
• Molar heat of vaporization : the heat required to vaporize one mole of liquid
ΔHfus• Molar heat of
fusion: the heat required to melt one mole of a solid substance
What happens in the reverse process?
ΔHvap = -ΔHcond
ΔHfus= -ΔHsolid
Molar enthalpy of condensation
Molar enthalpy of solidification
Changes of State
H2O(l) H2O(s) Δhsolid=-6.01 kJ
H2O(s) H2O(l) ΔHfus=6.01 kJ
Example:
• How many grams of ice at 0°C will melt if 2.25 kJ of heat at added?
Changes of State
H2O(l) H2O(g) ΔHvap=40.7 kJ
H2O(g) H2O(l) ΔHcond=-40.7 kJ
Example:
How much heat is absorbed when 24.8 g of H2O (l) and 101.3 kPa is converted to H2O(g) at 100°C?
Changes of State
H2O(l) H2O(g) ΔHvap=40.7 kJ
H2O(g) H2O(l) ΔHcond=-40.7 kJ
H2O(s) H2O(l) ΔHfus=6.01 kJ
H2O(l) H2O(s) ΔHsolid=-6.01 kJ
Calculate the heat required to melt 25.7 g of solid methanol at its melting point. ΔHfus= 3.22 kJ/mol
Hess’s Law
If you add 2 or more thermochemical equations to give a final equation, the you can also add the heats of reaction to give the final heat of reaction.
What is the enthalpy change in kJ for the following reaction?
2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)
Use the enthalpy changes for the combustion of aluminum and iron: 2Al(s) + 3/2O2(s) Al2O3(s); ΔH = -1676.0 kJ
2Fe(s) +3/2O2(s) Fe2O3(s); ΔH = -822.1 kJ
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Determine the heat of reaction for the reaction:
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
Using the following sets of reactions:
N2(g) + O2(g) 2NO(g) H = 180.6 kJ
N2(g) + 3H2(g) 2NH3(g) H = -91.8 kJ
2H2(g) + O2(g) 2H2O(g) H = -483.7 kJ
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4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
Using the following sets of reactions:
a. N2(g) + O2(g) 2NO(g) H = 180.6 kJ
b. N2(g) + 3H2(g) 2NH3(g) H = -91.8 kJc. 2H2(g) + O2(g) 2H2O(g) H = -483.7 kJ
Goal:
NH3:O2 :
NO:H2O:
Reverse and x 2 4NH3 2N2 + 6H2 H = +183.6 kJ Found in more than one place, SKIP IT (its hard).
x2 2N2 + 2O2 4NO H = 361.2 kJx3 6H2 + 3O2 6H2O H = -1451.1 kJ
Add it up!! Hess StyLe
b. 4NH3 2N2 + 6H2
H = +183.6 kJa. 2N2 + 2O2 4NO H = 361.2 kJ
c. 6H2 + 3O2 6H2O H = -1451.1 kJ
4NH3 + 2N2 + 6H2 + 5O2 2N2 + 6H2 + 4NO + 6H2O
ΔH = -906.3 kJ4NH3 + 5O2 4NO + 6H2O ΔH = -906.3 kJ
Is this reaction exothermic or endothermic?
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Determine the heat of reaction for the reaction:
C2H4(g) + H2(g) C2H6(g)
Use the following reactions:
C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l) H = -1401 kJ
C2H6(g) + 7/2O2(g) 2CO2(g) + 3H2O(l) H = -1550 kJ
H2(g) + 1/2O2(g) H2O(l) H = -286 kJConsult your neighbor if necessary.
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Determine the heat of reaction for the reaction:
Goal: C2H4(g) + H2(g) C2H6(g) H = ?
Use the following reactions:
C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l) H = -1401 kJ
C2H6(g) + 7/2O2(g) 2CO2(g) + 3H2O(l) H = -1550 kJ
H2(g) + 1/2O2(g) H2O(l) H = -286 kJ
C2H4(g) :use 1 as is C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l) H = -1401 kJ H2(g) :# 3 as is H2(g) + 1/2O2(g) H2O(l) H = -286 kJC2H6(g) : rev #2 2CO2(g) + 3H2O(l) C2H6(g) + 7/2O2(g) H = +1550 kJ
C2H4(g) + H2(g) C2H6(g) H = -137 kJ
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