CH 102 Spring 2026 – Discussion Worksheet 5 Name: ________________________________________
1. [McQuarrie 17–41] The gas-phase decomposition of CH3CHO(𝑔) occurs according to the equation:
CH3CHO(𝑔) ⟶ CH4(𝑔) + CO(𝑔), and is second order. The value of the rate constant is 0.105 M–1s–1 at 490 °C. If the
concentration of CH3CHO(𝑔) is 0.012 M initially, what will be its concentration 5.0 minutes later?
2. [McQuarrie 18–7] Write the rate law for each of the following elementary reaction equations. Also, for each of the
elementary reaction equations, state the overall order of the reaction and the order with respect to each reactant.
Classify the reaction as unimolecular, bimolecular, or termolecular.
a. N2O(𝑔) + O(𝑔) ⟶ 2NO(𝑔)
b. 2 O2(𝑔) ⟶ O(𝑔) + O3(𝑔)
c. ClCO(𝑔) + Cl2(𝑔) ⟶ Cl2CO(𝑔) + Cl(𝑔)
3. [McQuarrie 18–11] The reaction of carbon dioxide with hydroxide ion in aqueous solution described by
CO2(𝑎𝑞) + 2 OH−(𝑎𝑞) ⟶ CO32−(𝑎𝑞) + H2O(𝑙) is postulated to occur according to the mechanism:
(1) CO2(𝑎𝑞) + OH−(𝑎𝑞) ⟶ HCO3−(𝑎𝑞) (slow)
(2) HCO3−(𝑎𝑞) + OH−(𝑎𝑞) ⟶ CO32−(𝑎𝑞) + H2O(𝑙) (fast)
The rate law for the disappearance of CO2(𝑎𝑞) was found experimentally to be Rate = 𝑘[CO2][OH−]. Is this
mechanism consistent with the observed rate law? Justify your answer.
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1. [McQuarrie 17–41] The gas-phase decomposition of CH3CHO(𝑔) occurs according to the equation:
CH3CHO(𝑔) ⟶ CH4(𝑔) + CO(𝑔), and is second order. The value of the rate constant is 0.105 M–1s–1 at 490 °C. If the
concentration of CH3CHO(𝑔) is 0.012 M initially, what will be its concentration 5.0 minutes later?
2. [McQuarrie 18–7] Write the rate law for each of the following elementary reaction equations. Also, for each of the
elementary reaction equations, state the overall order of the reaction and the order with respect to each reactant.
Classify the reaction as unimolecular, bimolecular, or termolecular.
a. N2O(𝑔) + O(𝑔) ⟶ 2NO(𝑔)
b. 2 O2(𝑔) ⟶ O(𝑔) + O3(𝑔)
c. ClCO(𝑔) + Cl2(𝑔) ⟶ Cl2CO(𝑔) + Cl(𝑔)
3. [McQuarrie 18–11] The reaction of carbon dioxide with hydroxide ion in aqueous solution described by
CO2(𝑎𝑞) + 2 OH−(𝑎𝑞) ⟶ CO32−(𝑎𝑞) + H2O(𝑙) is postulated to occur according to the mechanism:
(1) CO2(𝑎𝑞) + OH−(𝑎𝑞) ⟶ HCO3−(𝑎𝑞) (slow)
(2) HCO3−(𝑎𝑞) + OH−(𝑎𝑞) ⟶ CO32−(𝑎𝑞) + H2O(𝑙) (fast)
The rate law for the disappearance of CO2(𝑎𝑞) was found experimentally to be Rate = 𝑘[CO2][OH−]. Is this
mechanism consistent with the observed rate law? Justify your answer.
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