Dr. C. Kozak
Chem 1050 Chapter 4 and 6 Review Questions
1. A sample of NH4NO3(s) is placed in a 3.60 L container where it completely decomposes at 195 °C according
to the following reaction:
NH4NO3(s) → N2O(g) + 2 H2O(g)
The total pressure of the gases in the container produced from the decomposition is 745 mmHg. Calculate
the mass of NH4NO3 that was placed in the container. [4]
A: 2.48 g
2. To a rigid container holding 22.7 L of H2(g) measured at 0 °C and 1 bar was added 12.005 g of CO(g) and
the temperature raised to 80 °C.
What is the resulting pressure of the gas mixture? [3]
A: 1.85 bar
3. If a catalyst is present, CO and H2 can react to form hydrocarbons like propane via the reaction below. If the
conditions above are used, briefly explain whether the pressure of the resulting products increases or
decreases? [1]
3CO(g) + 7H2(g) → C3H8(g) + 3H2O(l)
A: P decreases (P becomes 0.129 bar)
4. Chlorine gas, Cl2(g) has an effusion rate of 2.4 × 10-6 mol s-1. What would be the effusion rate for bromine
gas, Br2(g), in mol s-1, under the same conditions? [4]
A: 1.6 x 10-6 mol s-1
5. A 34.8 mL sample of an unknown, water insoluble gas was collected over water at 22.6 °C and a barometric
pressure of 0.895 bar. When the gas was dried and chilled, it formed 114.6 mg of liquid. What was the molar
mass of this substance? (hint: vapour pressure of water at 22.6 °C is 20.0 torr) [4]
A: 93.3 g mol-1
6. At STP conditions:
a. What is the density (in g/mL) of O2 gas? [2]
A: 1.41 x 10-3 g mL-1
b. Which gas is more dense, O2(g) or Ne(g)? Explain. [2]
A: O2(g), because larger molar mass
c. Which has the higher average kinetic energy, O2(g) or Ne(g)? Briefly justify your answer. [2]
A: Same KE, since E proportional to temperature, not molar mass
!!
7. The van der Waals equation is 𝑃 + 𝑎 ! ! 𝑉 − 𝑛𝑏 = 𝑛𝑅𝑇 NOT REQUIRED
a. The van der Waals constant, b, is 0.173 L mol-1 for hexane (C6H14) but only 0.64 L mol-1 for
ethane (C2H6). Briefly explain why. [1]
b. The pressure correction term, a, of a van der Waals gas takes into account what property of the
non-ideal gas? [1]
Dr. C. Kozak
8. An empty 200 g cylinder was filled with a gas mixture containing 7.5 mg H2S and balance N2. The mass of
the filled cylinder and the resulting pressure was determined to be 200.0575 g and 4.66 bar, respectively.
What is the partial pressure, in bar, of N2 in the cylinder? [4]
A: 4.2 bar
9. A 125.0 g sample of copper is heated to 100.0 ºC. It is dropped into 25.0 g of water at 21.2 ºC. The final
temperature of the water and copper is 46.0 ºC. What is the heat capacity of copper (in J mol-1)? [6]
A: 0.384 J g-1 °C-1
10.
1.0075 g of tetradecane (C14H30, molar mass = 198.388 g mol-1) is burned in a constant volume bomb
calorimeter containing excess oxygen. The calorimeter has a heat capacity of 4.681 kJ/K. The temperature of
the calorimeter is determined to increase from 293.32 to 303.86 K. Determine ΔU and ΔH for the
combustion of one mole of tetradecane at 298 K. [6]
C14H30(l) + 43/2 O2(g) → 14 CO2(g) + 15 H2O(l)
A: ΔH = -9886 kJ mol-1, ΔU = -9867 kJ mol-1
11.
Substitute natural gas is a gaseous mixture containing methane (CH4) and can be used as a fuel. One
reaction for the production of substitute natural gas is
4 CO(g) + 8 H2(g) → 3 CH4(g) + CO2(g) + 2 H2O(l)
Use the enthalpies of formation in the data below to determine the enthalpy for the above reaction. [6]
ΔHfº / kJ mol-1: CH4(g) -74.81
CO2(g) -393.5
CO(g) -110.5
H2O(l) -285.8
A: -1632 kJ mol-1
12.
Nitrogen oxides undergo many interesting reactions in the atmosphere. Calculate ΔH for the overall
equation [6]:
2 NO2(g) + 1/2 O2(g) → N2O5(s)
Given the following information:
N2O5(g) → 2 NO(g) + 3/2 O2(g)
NO(g) + 1/2 O2(g) → NO2(g)
ΔH = 223.7 kJ
ΔH = -57.1 kJ
A: -109.5 kJ mol-1
13.
Three 9.5 g ice cubes at -11 ºC are added to 230 mL of hot (42 ºC) water in a thermos. When the ice
cubes have melted, the equilibrium temperature of the water in the thermos is 29 ºC. What is the heat
capacity of the thermos? The specific heat of ice at -11 oC is 2.092 J/g·ºC. [6]
A: 84.58 J °C-1
Dr. C. Kozak
14.
A coffee-cup calorimeter contains 100.0 mL of 0.300 M HCl(aq) at 20.3 oC. When 1.82 g Zn(s) is
added, the temperature rises to 30.5 oC. Write a balanced equation for the reaction of Zn(s) with HCl(aq). [2]
A: Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
15.
What is the heat of reaction per mol Zn? Assume that the density and specific heats of the HCl(aq) are
the same as water, ignore the heat capacity of the coffee cup itself, and assume no heat is lost with the escape
of the H2(g). [5]
A: qZn = qP = -284.5 kJ mol-1 (because this is under constant P conditions, the molar heat of reaction is the
Enthalpy of the reaction). For an added component, does any work occur in this reaction? If you
assume an average T of 25 °C, can you determine it based on the information given?