Calculate the initial rate of reaction for experiment 2, if measured under the same conditions.
Experiment
Initial [CH3CHO]
/ mol dm-3
Initial [OH-]
/ mol dm-3
Initial rate
/ mol dm-3 s-1
1
0.25
0.20
4.2 x 10-2
2
0.25
0.30
Question 3e
Marks: 1
e)
State the effect, if any, increasing the concentration of a reactant would have on the value of the rate constant, k.
Question 4a
Marks: 1
a)
Nitrogen dioxide and carbon monoxide react according to the following equation.
NO2 (g) + CO (g) → NO (g) + CO2 (g)
Using the following graph, what is the order with respect to NO2?
Question 4b
Marks: 2
b)
The rate expression for the reaction of nitrogen dioxide and carbon monoxide at T < 227 OC is:
Rate = k [NO2]2
Sketch a labelled graph of concentration against time for carbon monoxide.
Question 4c
Marks: 2
c)
A student proposed the following single step mechanism for the reaction of nitrogen dioxide and carbon monoxide.
NO2 + CO → NO + CO2 slow
Rate = k [NO2]2
Justify whether the student’s proposed mechanism is correct.
Question 4d
Marks: 1
d)
Another student proposed the following mechanism for the reaction of nitrogen dioxide and carbon monoxide.
Step 1: NO2 + NO2→ NO + NO3 Step 2: NO3 + 2CO → NO + 2CO2
Rate = k [NO2]2
Explain which of the student’s proposed mechanism steps is the rate determining step.
Question 5a
Marks: 1
a)
Nitrogen(II) oxide is oxidised according to the following equation.
2NO (g) + O2 (g) → 2NO2 (g)
The following mechanism is proposed for the two-step oxidation of nitrogen(II) oxide.
Step 1: NO (g) + NO (g) → N2O2 (g) Step 2: N2O2 (g) + O2 (g) → 2NO2 (g)
The potential energy profile for this two-step reaction is shown.
Explain which step is the rate determining step.
Question 5b
Marks: 3
b)
Energy profile diagrams give evidence for or against a proposed mechanism or proposed rate expression.
i)
Explain why the rate expression for the oxidation of nitrogen(II) oxide is not rate = k [N2O2] [O2].
ii)
Deduce the rate expression for the oxidation of nitrogen(II) oxide.
Question 5c
Marks: 2
c)
Explain why the following reaction between iodide ions and peroxodisulfate ions has a high activation energy.
S2O82- (aq) + 2I- (aq) → 2SO42- (aq) + I2 (aq)
Question 5d
Marks: 2
d)
Sketch the potential energy diagram for the reaction of iodide ions with peroxodisulfate ions catalysed by iron(II) ions according to the following mechanism.
