Honors Chemistry - Chapter 17 Review Packet
Name: ______________________________
Chapter 17: Thermochemistry
Section 1: The Flow of Energy – Heat and Work
1. What is thermochemistry? The study of the energy changes that occur in changes of state or during
chemical reactions.
2. Heat always flows from a warmer object to a cooler object.
3. Given that 1 cal = 4.184 J:
a. How many calories are in 325.9 J? 77.89 cal
b. How many J are in 34.7 cal? 145.18 J
4. What is the Law of Conservation of Energy (aka the First Law of Thermodynamics)? States that in
chemical and physical processes, energy is neither created nor destroyed – it is transferred or
conserved.
5. In an exothermic reaction:
a. Heat is
released / absorbed
b. q is
positive / negative
c. ΔH is
positive / negative
d. Heat is a
reactant / product
6. In an endothermic reaction:
a. Heat is
released / absorbed
b. q is
positive / negative
c. ΔH is
positive / negative
d. Heat is a
reactant / product
7. Diagram A represents an exothermic reaction, whereas diagram B represents an endothermic reaction:
8. What is the difference between heat capacity and specific heat capacity? Specific heat is the amount of
energy to increase the temperature of 1g of substance by 1˚C
9. The temperature of a 34.1 g sample of a substance increases from 29 C to 51 C when the sample absorbs
912 J of heat. What is the specific heat of the substance? 1.126 J/g˚C
10. When 867 J of heat are added to 9.3 g of a substance at STP, the temperature increases from 0 C to 14 C.
What is the specific heat of the substance? 6.66 J/g˚C
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Honors Chemistry - Chapter 17 Review Packet
Name: ______________________________
11. How much heat (in J) is required to raise the temperature of 78.1 g of mercury by 92 C? The specific
heat of mercury is 0.14 J/g˚C. 1,005.93 J
Section 2: Measuring and Expressing Enthalpy Changes
1. What is calorimetry? Precise measurement of heat flow into or out of a system for a chemical
reaction or physical process
2. What is enthalpy? Heat content of s system
3. When 50 g of water containing dissolved NaOH are mixed with 90 g of water containing dissolved HCl
in a coffee cup calorimeter at 19 C, the temperature of the solution increases to 24 C. How much heat
was released by the reaction? (Cwater = 4.18 J/g˚C) -2,926 J
4. If 1.7 g of calcium is placed in 92 g of water in a coffee cup calorimeter at 27 C, the temperature
increases to 42 C. How much heat is released by the reaction? (Cwater = 4.18 J/g˚C) -5,768.4 J
5. A 19.2 mole sample of methane (CH4) is burned in a bomb calorimeter containing 8675.31 g of water at
an initial temperature of 18 C. The temperature increases to 34 C. The heat capacity of the calorimeter
is 697 J/˚C and the specific heat of water is 4.18 J/g˚C. Calculate qrxn. -591, 356.7 J (This type of
problem will be a bonus opportunity on tomorrow’s quiz!!)
6. Given the following unbalanced equation: CH4 + O2  CO2 + H2O and a ΔH of -890.0 kJ.
a. Write the balanced thermochemical equation. CH4 + 2 O2  CO2 + 2H2O + 890 kJ
b. Is the reaction exothermic or endothermic? Exothermic
c. How much heat is given off by the reaction of 8.9 g of CH4? 495.1 kJ
d. How many grams of O2 are required to react to produce 12,487 kJ of heat? 897.94 g
Section 3: Heat in Changes of State
1. How much heat, in kJ, is required to completely melt 92.7 g of ice? The ΔHfus is 6.01 kJ/mol for water.
30.95 kJ
2. How much heat, in kJ, is required to boil 13.2 g of ammonia? The ΔHvap is 23.4 kJ/mol for ammonia.
18.17 kJ
3. How many grams of ice at 0 C will melt if 75.4 kJ of heat are applied? The ΔHfus is 6.01 kJ/mol for
water. 225.8 g
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Honors Chemistry - Chapter 17 Review Packet
Name: ______________________________
4. Label the heating curve and answer the questions below:
65˚C
25˚C
a. What is the melting point of this substance? 25˚C
b. What is the boiling point of this substance? 65˚C
c. Why does the temperature briefly stop increasing in regions B and D? All energy goes into the
phase change that is occurring rather than increasing the temperature. As soon as the
phase change is complete, the temperature starts to increase again.
Section 4: Calculating Heats of Reaction
1. ___ NaOH(s) + ___ HCl(aq)  ___ NaCl(s) + ___H2O(l)
Given ΔHf0 values:
NaOH(s) = -426.7 kJ/mol
HCl(aq) = -167.16 kJ/mol
H2O(g) = -241.8 kJ/mol
HCl(g) = -92.3 kJ/mol
NaCl(c) = -411.2 kJ/mol
H2O(l) = -285.8 kJ/mol
ΔH0 = [(1 mol x -411.2 kJ/mol) + (1 mol x -285.5 kJ/mol)] – [(1 mol x -426.7 kJ/mol) + (1 mol x -167.16 kJ/mol)]
ΔH0 = (-697 kJ) – (-593.86 kJ) = -103.14 kJ
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Honors Chemistry - Chapter 17 Review Packet
Name: ______________________________
2. What is the ΔHf0 for the reaction between butane (C4H10) and oxygen to form carbon dioxide gas and
water vapor? Start with a balanced chemical equation.
Given ΔHf0 values:
C4H10 (g) = -2866 kJ/mol
CO2 (g) = -393.5 kJ/mol
O2 (g) = 0.0 kJ/mol
H2O(g) = -241.8 kJ/mol
H2O(l) = -285.8 kJ/mol
2 C4H10 (g) + 3 O2 (g)  8 CO2 (g) + 10 H2O (g)
ΔH0 = [(8 mol x -393.5 kJ/mol) + (10 mol x -214.8 kJ/mol)] – [(2 mol x -2866 kJ/mol) + (3 mol x 0 kJ/mol)]
ΔH0 = (-5,566 kJ) – (-5,732 kJ) = 166 kJ
3. Find the ΔH for the following reaction: 2 Mg(s) + SiCl4 (l)  Si(s) + 2 MgCl2 (s)
Given:
Si(s) + 2 Cl2 (g)  SiCl4 (l)
Mg(s) + Cl2  MgCl2 (s)
ΔH = -687 kJ
ΔH = -641 kJ
(REVERSE)
(MULTIPLY BY 2)
ΔH = -595 kJ
4. Find the ΔH for the following reaction: 2 NO2 (g) → N2O4 (g)
Given:
N2 (g) + 2 O2 (g)  N2O4 (g)
N2 (g) + 2 O2 (g)  NO2 (g)
∆H = +9.67 kJ
∆H = +67.78 kJ
ΔH = -58.11 kJ
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(STAYS SAME)
(REVERSE)