Chemistry 110
Thermochemistry
Practice Problems
1. If it takes 41.72 joules to heat a piece of gold weighing 18.69g from 10.0ᵒC to
27.0ᵒC, what is the specific heat of the gold ?
=0.131J/gdeg
2. The specific heat of ethanol is 2.46 J/gᵒC. Find the heat required to raise the
temperature of 193 g of ethanol from 19ᵒC to 35ᵒC.
7596J
3. How many Joules of energy are needed to raise the temperature of 125g of a
solid from 25.0°C to 52.6°C? The specific heat of the solid Is 0.475J/g°C. SHOW
ALL WORK !!!!!
1
4. a. Calculate the ∆HRXN for the following balanced equation.
2 H2S (g)
+
3 O2(g)
→
Chemical
2 H2O (l)
+
2 SO2(g)
∆H
H2S(g)
-20.1 kJ/mole
H2O(l)
-285.8 kJ/mole
SO2(g)
-296.1 kJ/mole
O2 (g)
0 kj/mol
b. Is the above reaction endothermic or exothermic ?
_____Exo___________
-1123.6 kJ
5. a. Calculate the ΔHᵒRXN for the following balanced equation.
C2H5OH (l)
+
3 O2(g)
→
Chemical
2 CO2 (g)
+
3 H2O (l)
ΔHᵒf
C2H5OH (l)
-228 kJ/mol
CO2(g)
-394 kJ/mol
H2O (l)
-286 kJ/mol
O2 (g)
0 kj/mol
b. Is the above reaction endothermic or exothermic ? ___________________
2
6. The combustion of methane gas is represented by the reaction:
CH4 (g)
+
2 O2 →
Calculate the ∆ H
CO2(g)
+
2 H2O (g)
°
given the following information.
rx
Substance
∆Hf°
CH4
- 74.8 kJ/mole
O2
0 kJ/mole
CO2
-393.5 kJ/mole
H2O
-241.8 kJ/mole
b. Is the above reaction endothermic or exothermic ? ____exo____________
-802 KJ
7. Given the following information, calculate the ∆H for the target reaction.
SHOW ALL WORK !!!!!
Target:
NO2(g) + 7 ⁄2H2(g) ---> 2H2O(l) + NH3(g)
3
Given:
1.) 2NH3(g) ---> N2(g) + 3H2(g) ΔH° = +92 kJ
2.) 1 ⁄2N2(g) + 2H2O(l) ---> NO2(g) + 2H2(g) ΔH° = +170 kJ
8. Given the following information, calculate the ∆H for the target reaction.
SHOW ALL WORK !!!!!
Target:
2 CH4(g) + 3 O2(g) ---> 2 CO(g) + 4 H2O(l)
Given: 1.) CH4(g) + 2 O2(g) ---> CO2(g) + 2 H2O(l) ∆H°= -890.0 kJ
2.) 2 CO(g) + O2(g) ---> 2 CO2(g) ∆H°= -566.0 kJ
4
9. Calculate the ∆H for the following reaction:
SHOW ALL WORK!!!!!!!!!!!!
Target: 2C2H4(g) + H2O(l) → C4H9OH(l)
Given:
1. 2CO2(g) + 2H2O(l) → C2H4(g) + 3O2(g) ∆H = +1411.1 kJ
2. C4H9OH(l) + 6O2(g) → 4CO2(g) + 5H2O(l) ∆H = -1534.7 kJ
5