AP Chemistry - Thermochemistry Review Worksheet
1.  Write thermochemical equations for the combustion of one mole of each of the following compounds. The products in each case are gaseous carbon dioxide and liquid water. (Standard conditions are assumed.) The numbers given in parentheses after each formula are the standard heats of combustion. 

(a) Acetylene, C2H2(g) (-1299.6 kJ/mol) 

(b) Methyl alcohol, CH3OH(l) ( -726.51 kJ/mol) 

(c) Diethyl ether, C4H10O(l) (-2751.1 kJ/mol)

(d) Toluene, C7H8(l) (-3909.0 kJ/mol) 
 
2.  Palmitic acid, C16H32O2, is typical of the materials available from fats and oils insofar as chemical energy is concerned. 

(a) Write the thermochemical equation of the complete combustion of one mole of this compound, a solid, assuming that gaseous carbon dioxide and liquid water form. The standard heat of combustion of palmitic acid is -9957.92 kJ/mol. 

(b) Using the molar heat of combustion of palmitic acid and data from the appropriate source, estimate the Hfo for palmitic acid. 
 
3. Construct an enthalpy diagram that shows the enthalpy changes for a one-step conversion of germanium, Ge(s), into its dioxide, GeO2(s), and a two-step conversion - first to the monoxide, GeO(s), and then the oxidation of the monoxide to the dioxide. The relevant thermochemical equations are as follows. 

Ge(s) + ½ O2(g) -----> GeO(s)          Ho = -255 kJ 

Ge(s) + O2(g) -----> GeO2(s)          Ho = -534.7 kJ 

Using this diagram, determine the value of Ho for the reaction

GeO(s) + ½ O2(g) -----> GeO2(s) 
 
4. Calculate Ho for the following reaction, which describes the preparation of an unstable acid, HNO2, nitrous acid. 

HCl(g) + NaNO2(s) ----> HNO2(l) + NaCl(s) 

Use the following thermochemical equations. Calculate the answer in kilojoules.

2 NaCl(s) + H2O(l) --> 2 HCl(g) + Na2O(s)           Ho = +507.3 kJ 

NO(g) + NO2(g) + Na2O(s) ----> 2 NaNO2(s)          Ho = -427.14 kJ 

NO(g) + NO2(g) -----> N2O(g) + O2(g)          Ho = -42.68 kJ 

2 HNO2(l) -----> N2O(g) + O2(g) + H2O(l)          Ho = +34.35 kJ 
 
5.  The standard heat of formation of gaseous hydrogen bromide was first evaluated by means of the standard enthalpy values measured for the following reactions. The last three are standard heats of solution. 

Cl2(g) + 2 KBr(aq) ----> Br2(aq) + 2 KCl(aq)          Ho = -96.2 kJ 

H2(g) + Cl2(g) ----> 2 HCl(g)                                   Ho = -184 kJ 

HCl(aq) + KOH(aq) ----> KCl(aq) + H2O(l)           Ho = -57.3 kJ 

HBr(aq) + KOH(aq) ----> KBr(aq) + H2O(l)          Ho = -57.3 kJ 

HCl(g) --------> HCl(aq)                                        Ho = -77.0 kJ 

Br2(g) --------> Br2(aq)                                          Ho = -4.2 kJ 

HBr(g) --------> HBr(aq)                                        Ho = -79.9 kJ 

Write the thermochemical equation for the formation of 1 mol of HBr(g) from its elements, including its value for Hfo