The document is a study guide for a general chemistry exam that includes 8 questions covering topics like: 1) Calculating enthalpy changes for chemical reactions using given enthalpy of formation values 2) Calculating standard enthalpy change values (ΔH°) for chemical reactions using reference tables 3) Calculating standard enthalpy of formation for diborane gas using thermochemical data 4) Defining fuel value and comparing the energy provided by fat and carbohydrates 5) Calculating the caloric content of alcohol in wine using given ethanol content and heat of combustion values 6) Explaining why fats are suitable for energy storage and calculating the percentage of calories from fat in a

1. GENERAL CHEMISTRY-I (1411)
S.I. # 23
1. Calculate the enthalpy change for the reaction
P4O6 (s) + 2 O2 (g)  P4O10 (s)
Given the following enthalpies of reaction:
P4 (s) + 3 O2 (g)  P4O6 (s) ∆H = - 1640.1 kJ
P4 (s) + 5 O2 (g)  P4O10 (s) ∆H = -2940.1 kJ
2. Calculate the value of ∆H° for each of the following reactions. Use Appendix C of
your chemistry book.
a) N2O4 (g) + 4 H2 (g)  N2 (g) + 4 H2O (g)
b) 2 KOH (s) + CO2 (g)  K2CO3 (s) + H2O (g)
c) SO2 (g) + 2 H2S (g)  3/8 S8 (s) + 2 H2O (g)
d) Fe2O3 (s) + 6 HCl (g)  2 FeCl3 (s) + 3 H2O (g)
3. a) Calculate the standard enthalpy of formation of gaseous diborane (B2H6) using
the following thermochemical information:
4B (s) + 3 O2 (g)  2B2O3 (s) ∆H° = -2509.1 kJ
2H2 (g) + O2 (g)  2 H2O (l) ∆H° = -571.7 kJ
B2H6 (g) + 3 O2 (g)  B2O3 (s) + 3 H2O (l) ∆H° = -2147.5 kJ
4. a) what is meant by the term fuel value? b) Which is a greater source of energy as
food, 5 g of fat or 9 g of carbohydrates?

2. 5. The heat of combustion of ethanol, C2H5OH (l) is -1367 kJ/mol. A batch of wine
contains 10.6% ethanol by mass. Assuming the density of the wine to be 1.0g/mL,
what caloric content does the alcohol (ethanol) in a 6-oz glass of wine (177 mL)
have?
6. a) Why are fats well suited for energy storage in the human body? b) A
particular chip snack food is composed of 12% protein, 14% fat, and the rest
carbohydrate. What percentage of the calorie content of this food is fat? c) How
many grams of protein provide the same fuel value as 25g of fat?
7. Write balanced equations that describe the formation of the following
compounds from their elements in their standard states, and use Appendix C to
obtain the values of their standard enthalpies of formation: a) HBr (g), b) AgNO3
(s), c) Hg2Cl2 (s), d) C2H5OH (l).
8. Suppose that the gas-phase reaction 2NO (g) + O2 (g)  2 NO2 (g), were carried
out in a constant –volume container at constant temperature. Would the measured
heat change represent ∆H or ∆E? If there is a difference, which quantity is larger
for this reaction? Explain.