SCH4U: Thermochemistry and Rates of Reactions Unit Test Total:
Name: __________________________
/30
Date: _____________
Answer each question on a separate piece of paper.
1. Under certain condition, ammonia and oxygen can react as shown by the equation
4NH3(aq) + 5O2(g)  4NO(g) + 6H2O(g)
When the instantaneous rate of consumption of ammonia is 4.0 x 10-2 mol/Ls what will be the
instantaneous rate of (a) consumption of oxygen? (b) formation of water vapour? (2 marks)
2. Using the collision theory, explain how i) concentration and ii) temperature affect the rate
of a reaction. (2 marks each = 4 marks) (No more than 5 sentences in total)
3. 10.0 g of a fuel are burned under a calorimeter containing 200.0 mL of H2O. The temperature
of the water increases from 15.0 °C to 55.0 °C. Calculate the total heat of combustion per gram of
fuel. (2 marks)
4. A chemist wants to determine the enthalpy of neutralization for the following reaction:
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
The chemist uses coffee-cup calorimeter to neutralize completely 61.1 ml of 0.5 mol/L HCl with
42.6 ml of NaOH. The initial temperature of both solutions is 17.8C. After neutralization, the
highest recorded temperature is 21.6C. Calculate the enthalpy of neutralization, in units of kJ/mol
of HCl. Assume that the specific heat capacity of both solution is the same as the specific heat
capacity of water. (3 marks)
5. Calcium oxide, CaO, reacts with carbon in the form of graphite. Calcium carbide, CaC2, and
carbon monoxide are produced in an endothermic reaction. (3 marks)
CaO (s)+ 3C (s) + 462.3 kJ  CaC2(s) + CO(g)
a. 245 kJ of energy is available to react. What mass of calcium carbide is produced, assuming
sufficient reactants? (2 marks)
b. 2.5 mol of calcium oxide react with excess graphite. How much energy is needed? (1 mark)
6. Calculate the
Hfo for 6 C(s) + 6 H2 (g) + 3 O2 (g)
C6H12O6 (s) + 6 O2 (g)
H2 (g) + 1/2 O2 (g)
C (s) + O2 (g)
C6H12O6 (s) given that:
6 CO2 (g) + 6 H2O (g)
H2O (g)
CO2 (g)
(3 marks)
Hc = -2537.3 kJ
Hfo = -241.8 kJ
Hfo = -393.5 kJ
7. Determine the enthaply for the reaction of ammonia with oxygen using the enthalpies of
formations found in the table. (3 marks)
Hof (kJ/mol)
4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g)
8. Consider the following reaction mechanism:
Step 1: 2 NO + H2  N2 + H2O2
Step 2: H2 + H2O2  2 H2O
NH3(g)
O2(g)
NO(g)
H2O(g)
-46
0
+90
-242
Ea1 = 50 kJ
Ea2 = 10 kJ
a) What is the overall reaction? (1 mark)
b) Which step is the rate determining step and why (1 marks)
c) What are/is the reaction intermediate(s)? (1 mark)
d) H for the overall reaction is -30 kJ. Sketch the potential energy diagram showing the two
steps. Label Ea1 and Ea2. Label Activated Complexes, and reaction intermediates. Label H as
well. (5 marks)
e) What is the overall Ea for this reaaction? (1 mark)