Name_______________________________
1. The bombardier beetle uses an explosive discharge as a defensive measure. The
chemical reaction involved is the oxidation of hydroquinone by hydrogen
peroxide to produce quinone and water:
C6H4(OH)2(aq) + H2O2(aq)  C6H4O2(aq) + 2H2O(l)
Calculate H for this reaction from the following data:
C6H4(OH)2(aq)  C6H4O2(aq) + H2 (g)
H = +177.4 kJ
H2(g) + O2(g)  H2O2(aq)
H = -191.2 kJ
H2(g) + ½ O2(g)  H2O (g)
H = -241.8 kJ
H2O(g)  H2O(l)
H = -43.8 kJ
2. A hot air balloon is being inflated to its full extent by heating the air inside it. In
the final stages of this process, the volume of the balloon changes from 3.5 x 106
L to 4.50 x 106 L by the addition of 13 MJ of energy as heat. Assuming that the
balloon expands against a constant pressure of 1.2 atm, calculate E for the
process. To convert between L atm and J, use 1 L atm = 101.3 J.
3. For the reaction
S(s) + O2(g) SO2(g)
H = -296 kJ/mol
a. How much heat is evolved when 2.5 mol sulfur is burned in excess O2?
4. Answer the following questions on thermochemistry:
Substance
Combustion Reaction
H2(g)
H2(g) + ½ O2(g)  H2O(l)
Enthalpy of Combustion,
Hocomb, at 298 K (kJ mol-1)
-290
C(s)
C(s) + O2(g)  CO2(g)
-390
CH3OH(l)
-730
a. In the empty box in the table above, write a balanced equation for the
complete combustion of one mole of CH3OH(l). Assume products are in their
standard states at 298 K. Coefficients do not need to be whole numbers.
b. On the basis of your answer to part “a” and the other information in the table,
determine the enthalpy change for the reaction
C(s) + 2 H2(g) + ½ O2 (g)  CH3OH(l) .
5. A student performs an experiment to determine the molar enthalpy of solution of
urea, H2NCONH2. The student place 91.95 g of water at 25oC into a coffee-cup
calorimeter and immerses a thermometer in the water. After 50 s, the student
adds 5.13 g of solid urea, also at 25oC, to the water and measures the temperature
of the solution as the urea dissolves. A plot of the temperature data is shown in
the graph below.
a. Determine the change in temperature of the solution that results from the
dissolution of the urea.
b. According to the data, is the dissolution of urea in the water an endothermic
process or an exothermic process? Justify your answer.
c. Assume that the specific heat capacity of the calorimeter is negligible and that the
specific heat capacity of the solution of urea and water is 4.2 J/ g oC throughout
the experiment.
i.
Calculate the heat of dissolution for the solution made of urea AND
water in joules.
ii.
Calculate the molar enthalpy of solution, Hosoln, of urea in kJ/ mo1
urea.
6. Reactions: Please write the unbalanced net ionic equation for each of the following:
a. Calcium oxide is added to distilled water.
b. Lead(II) nitrate solution is mixed with a solution of potassium iodide.
c. Sulfurous acid is added to an excess solution of sodium hydroxide.
d. Solid barium carbonate is strongly heated.