M5S2 – Kinetics 2

The graph from an experiment to study the decomposition of hydrogen peroxide shows how the concentration of the hydrogen peroxide varied with time at constant temperature.

Time = 0 minutes, [H₂O₂] = 0.020 mol dm^-3

Time = 654 minutes, [H₂O₂] = 0.010 mol dm^-3

Time = 1308 minutes, [H₂O₂] = 0.005 mol dm^-3

This suggests that, under the conditions of the experiment:

(i) the reaction is zero order with respect to hydrogen peroxide

(ii) the concentration after 1962 minutes was 0.0025 mol dm^-3

(iii) the rate of reaction was constant for the first 654 seconds

(iv) the half-life of the reaction was 654 minutes

The activation energy for the reaction

A + B -> C + D is 38 kJ mol^-1

The activation energy for the reaction

C + D -> A + B is 65 kJ mol^-1

There is a catalyst which lowers the activation energy for the reaction of A with B by 10 kJ mol^-1.

This shows that:

(i) the reaction of A with B is exothermic

(ii) the enthalpy change for the reaction of C with D is +27 kJ mol^-1

(iii) in the presence of the catalyst the activation energy for the reaction of C with D is 55 kJ mol^-1

(iv) the reaction of A with B is overall second order.

The reaction of hydrogen gas with nitrogen monoxide gas is first order with respect to H_2(g) and second order with respect to NO_(g). It follows that:

(i) rate = k[H_2(g)][NO_(g)]²

(ii) doubling the concentration of NO_(g) increases the rate by a factor of 4

(iii) the overall order of reaction is 3

(iv) halving the concentration of hydrogen reduces the rate by a factor of 1.

The activation energy for the reaction of cobalt metal with aqueous S₂O₈^2- ions is close to 50 kJ mol^-1. The rate of reaction for the metal when a cylinder of cobalt metal rotates rapidly in a solution of aqueous S₂O₈^2- ions at 15^oC is 1.80 mg min^-1. This suggests that at 25^oC the rate of reaction would be about:

The reaction of bromine with propanone in acid solution is zero order with respect to bromine, first order with respect to propanone and first order with respect to hydrogen ions.

At a given temperature, the rate of disappearance of bromine is 1.20 x 10^-4 mol dm^-3 when

[CH₃COCH₃] = 0.30 mol dm^-3

[Br₂] = 0.05 mol dm^-3

[H+] = 0.10 mol dm^-3

What is the rate of disappearance bromine when

[CH₃COCH₃] = 0.10 mol dm^-3

[Br₂] = 0.10 mol dm^-3 and [H+] = 0.05 mol dm^-3?

The rate equation for the decomposition of gaseous ethanal takes the form:

rate =k[CH₃CHO]²

The rate of reaction = 0.080 mol dm^-3 s^-1 when the concentration of ethanal = 0.20 mol dm^-3.

The value of the rate constant is:

The decomposition of dinitrogen pentoxide gas into nitrogen and oxygen is first order with respect to N₂O₅. The units of the rate constant are:

Nitrogen monoxide gas reacts with oxygen gas to form nitrogen dioxide gas. If the rate of formation of nitrogen dioxide is 1.4 x 10^-5 mol dm^-3, what is the rate of disappearance of oxygen?

Which technique would you use to measure the rate of reaction for the hydrolysis of ethyl ethanoate?

What does the symbol [X] represent?