Thermochemistry Review Worksheet.
True or False
If the answer is false, you must explain why.
1. _____ Chemical energy is a form of kinetic energy.
2. _____ When we mix water at 100C with water at 20C the final water temp. is always 60C.
3. _____ When we put a 100g piece of metal at 100C into 100g of water at 20C the final
temp is 20C.
4. _____ The term H stands for H final – H initial .
5. _____ A process in which the system absorbs heat from its surroundings is called
exothermic.
6. _____ A process in which the system absorbs heat from its surroundings has a positive
sign for H.
7. _____ The process described by the equation below is exothermic.
H 2 (g) + I 2 (g)  2HI(g) + heat
8. _____If the temperature of a reaction mixture in a coffee cup calorimeter increases as the
reaction proceeds, the reaction is endothermic, because the mixture is absorbing heat
heat from the surrounding air.
9. _____ Hess’s Law is true because enthalpy is a state function.
10. _____ The enthalpy change at standard conditions for the reaction below is referred to the
standard molar enthalpy of formation because this is a standard formation reaction.
H 2 (g) + I 2 (g)  2HI(g)
11. _____ The enthalpy change at standard conditions for the reaction below is referred to the
standard molar enthalpy of formation because this is a standard formation reaction.
½H 2 (g) + ½I 2 (g)  HI(g)
12. _____ The enthalpy change at standard conditions for the reaction below is referred to the
standard molar enthalpy of formation because this is a standard formation reaction.
CO(g) + ½O 2 (g)  CO 2 (g)
Short Answer
13. The symbol for heat is _____ .
14. The symbol for the change in enthalpy at any conditions is _____ .
Thermochemistry Review Worksheet.
15. The symbol for the change in enthalpy at standard conditions is _____ .
16. q = H at constant ____________ .
17. The sample or portion of the universe that we wish to study or describe in thermodynamics is
called the ___________________.
18. The First Law of Thermodynamics says that heat may neither be ___________ nor
_____________ in a chemical reaction.
19. A reaction in which the total (potential) energy of the products is greater than the total (potential)
energy of the reactants is said to be ____________ .
20. When we reverse a chemical equation, we multiply its H value by ________ .
21. A reaction in which the total heat content of the products is lower than the total heat content of
the reactants is said to be ___________ .
22. A reaction in which the system absorbs heat from its surroundings has a value of H that is
_______________
Calculations
23. Given the following reactions and their associated enthalpy changes:
CH 4 (g)  C(g) + 4H(g)
O 2 (g)  2O(g)
H 2 O(g)  2H(g) + O(g)
CO 2 (g)  C(g) + 2O(g)
H = 1663. kJ/mol
H = 498. kJ/mol
H = 927. kJ/mol
H =1608. kJ/mol
(equ #1)
(equ #2)
(equ #3)
(equ #4)
Use these values to calculate H for the combustion (burning) of 1 mole of methane (CH 4 ).
Hint: Start by writing the equation for the combustion reaction and then apply Hess’s Law..
CH 4 (g) + 2O 2 (g)  2H 2 O(g) + CO 2 (g)
24. Compare the value for the heat of combustion that you would get using the standard molar
enthalpy of formation values below.
H f  = -74.6 kJ/mol for CH 4 (g), H f  = -393.5 kJ/mol for CO 2 (g), and
H f  = -241.8 kJ/mol for H 2 O(g).