1. 2011 Honors Thermochemistry Study Guide Key
1. The study of heat changes that accompany chemical reactions and phase changes is
_thermochemistry_______________.
2. _Heat_________ (q) – Energy that is in the process of flowing from a warmer object
to a cooler object. Heat is measured by _temperature________________.
3. _Endothermic____________ Reactions are chemical reactions that must absorb energy
in order to occur. The ∆ H rxn charge is always positive_____________.
4. _Enthalpy__________– (H) -the heat content of a system at constant pressure.
5.____Potential___________ energy is the stored energy an object has based on its
position or composition.
6. _Combustion____________________ The enthalpy change for the complete burning
of 1 mole of the substance.
7. The Law of ___Conservation of Energy______________________ states that in any
chemical reaction or physical process, __energy_________ can be converted from 1 form
to another, but it is neither created nor destroyed.
8. _Kinetic_____________ energy is energy of motion
9. __Specific Heat__________________ is the amount of heat required to raise the
temperature of 1 g of a substance by 1° C
10. _Energy__________- the capacity to do work or to transfer heat.
11. _calorie___________________ is the amount of heat required to raise the
temperature of 1 g water by 1° C
12. __Exothermic_____________ reactions are chemical reactions that release energy.
The ∆ H rxn charge is always __negative_______________.
Energy Conversions
1 Calorie = _1_____ kilocalorie = ____1000___ calories
1 calorie = ___4.184_______ joules
1 kilojoule = __1000______ joules
1. Convert 42.3 Calories to kilojoule
176.98
2. Convert 0.050 kilocalories to joules
209.2
3. Convert 13.8 joules to Calories
0.0033
4. Convert 27 kilojoules to calories
6453.15
5. Convert 23.3 Calories to joules
97487.2
6. Convert 380 kilojoules to kilocalories
90.82

2. Specific Heat
1. It took 137.2 J of heat to raise the temperature of 15.7 g of a substance by 52 º
C. What is the specific heat of the substance?
0.16
2. When 32.4 g of zinc absorbs 105 J of heat energy, what is the change in
temperature of the metal?
8.31
3. Determine the amount of heat released if 11.5 g of lead melted with a change
in temperature of 34.3 º C.
63.112
4. A sample of magnesium cooled from 90.6 º C to 37.6 º C and produced 2329
joules of energy. What was the mass of the sample?
43.08
Calorimetry
1. A sample of silver with a mass of 40.1 g is heated to a temperature of 95.6 °C
and placed in a container of water at 23.5 °C. The final temperature of the
silver and water is 76.5 °C. What mass of water was in the container?
0.82
2. A 250 g sample of an unknown solid is heated to 87 °C and placed into a
calorimeter containing 25.6 g of water at 32.4 °C . If the final temperature of
the solid sample and the water is 54.6 °C , what is the specific heat of the
solid?
0.29
3. A 67 g sample of iron metal is heated and put into 10.5 g of water at 98.7 °C
in a calorimeter. If the final temperature of the iron sample and the water is
122.8 °C, what was the temperature of the iron sample when it was placed in
the water?
158.39
4. A sample of aluminum with a mass of 42 g is heated to a temperature of 62.5
°C and placed in a container of water at 26 °C. The final temperature of the
aluminum and water is 59.8 °C. What mass of water was in the container?
0.72

3. Enthalpy
Identify the type of reaction and whether it is endothermic or exothermic:
1. CaCO3 (l)  CaO (g) + CO2 (g) vaporization endothermic
2. NH3 (g)  NH3 (l) condensation exothermic
3. S (l) + O2 (l)  SO2 (s) solidification exothermic
4. NH4NO3 (s)  NH4 (l) + NO3 (l) fusion endothermic
5. CH4 + O2  CO2 + H2O combustion exothermic
6. How much energy is released by burning 75.6 grams of ethanol? 2242.88
7. How much energy is released by melting 42.3 grams of methanol? 4.26
8. How much energy is absorbed by 1.7 moles of water becoming steam? 69.19
9. How much energy is released by 88.2 grams of water condensing to a liquid?
199.43
10. How much energy is absorbed by 7.3 grams of liquid ammonia becoming a solid?
2.43
11. Calculate the total energy required to pass through each phase in order to melt
75.5 grams of ice from – 36.5 oC to 146 oC. Show each calculation and the total
amount.
239.9
Hess’ Law and Heat of Formation
1) Given that the heat of formation of calcium carbonate is –1207 kJ/mol, the heat of
formation of carbon dioxide is –394 kJ/mol, and the heat of formation of calcium
oxide is –635 kJ/mol, determine the heat of reaction.
CaCO3  CO2 + CaO
178
2) Given that the heat of formation of methane is –75 kJ/mol and the heat of
formation of carbon tetrachloride is –135 kJ/mol, determine the heat of reaction.
CH4 + 2 Cl2  CCl4 + 2 H2
-60
3) Given that the heat of formation of potassium chloride is –436 kJ/mol and the heat
of formation of potassium chlorate is –391 kJ/mol, determine the heat of reaction.
2 KCl + 3 O2  2KClO3
90
4) Calculate the heat of reaction for the formation of barium sulfate and water.
BaO + H2SO4  BaSO4 + H2O ∆H = ?
a) BaO + SO3  BaSO4 ∆H = -213 kj

4. b) SO3 + H2O  H2SO4 ∆H = -78 kj
-135
5) Calculate the heat of reaction for the formation of Tin (IV) chloride.
Sn + 2 Cl2  SnCl4 ∆H = ?
a) Sn + Cl2  SnCl2 ∆H = -325 kj
b) SnCl2 + Cl2  SnCl4 ∆H = -186 kj
-511
Entropy
1. ___entropy_____________ (S) – a measure of the disorder or randomness of the
particles that make up a system
2. _spontaneous_reaction_______________ – a change that occurs with no outside
intervention.
3. Law of _Disorder/entropy____________– Spontaneous processes always proceed in a
way that the entropy of the universe _increases____________.
Describe the movement and order of molecules in the following phases:
4. Solids –no movement, low entropy
5. Liquids – little movement, some entropy
6. Gas – lot of movement, high entropy
7. Entropy __decreases__________ as a substance changes from gasliquidsolid.
Does entropy INCREASE or DECREASE with the following phase changes:
8. As methanol (l) solidifies (s) _decrease_______________
9. As ice (s) turns to vapor (g) _increase_______________
10. As water (g) condenses (l) _decrease_______________
11. As water (l) vaporizes (g) _increase______________
12. As a metal (s) melts to liquid (l) _increase_______________
13. As methanol (g) turns to methanol (s) _decrease_______________