Question
Alex and Hannah were asked to investigate the kinetics involved in the iodination of propanone. They were given the following equation by their teacher.
CH3COCH3 (aq) + I2 (aq) → CH2ICOCH3 (aq) + HI (aq)
Alex's hypothesis was that the rate will be affected by changing the concentrations of the propanone and the iodine, as the reaction can happen without a catalyst. Hannah's hypothesis was that as the catalyst is involved in the reaction, the concentrations of the propanone, iodine and the hydrogen ions will all affect the rate.
They carried out several experiments varying the concentration of one of the reactants or the catalyst whilst keeping other concentrations and conditions the same, and obtained the results below.
| Experiment | [CH3COCH3] (mol dm-3) | [I2] (mol dm-3) | [H+] (mol dm-3) | Rate (mol dm-3 s-1) |
|---|---|---|---|---|
| 1 | 320 | 600 | 818 | 3.45 × 10-7 |
| 2 | 320 | 600 | 273 | 1.15 × 10-7 |
| 3 | 306 | 600 | 818 | 3.29 × 10-7 |
| 4 | 306 | 611 | 818 | 3.35 × 10-7 |
a. Explain why they added water to the mixtures.
[1]
b.
(i) Deduce the order of reaction for each substance and the rate expression from the results.
(ii) Comment on whether Alex’s or Hannah’s hypothesis is correct.
[3]
c. Using the data from Experiment 1, determine the concentration of the substances used and the rate constant for the reaction including its units.
[3]
d.
(i) This reaction uses a catalyst. Sketch and annotate the Maxwell-Boltzmann energy distribution curve for a reaction with and without a catalyst on labelled axes below.
(ii) Describe how a catalyst works.
[3]
Question
Consider the following reaction.
5Br- (aq) + BrO3- (aq) + 6H+ (aq) → 3Br2 (aq) + 3H2O (l)
The rate expression for the reaction is found to be:
rate = k[Br-][BrO3-][H+]2
Which statement is correct?
A. The overall order is 12.
B. Doubling the concentration of all of the reactants at the same time would increase the rate of the reaction by a factor of 16.
C. The units of the rate constant, k, are mol dm-3s-1.
D. A change in concentration of Br- or BrO3- does not affect the rate of the reaction.
Question
Consider the rate expression:
Rate = k[X][Y]
Which change decreases the value of the rate constant, k?
- A. Increase in the reaction temperature
- B. Decrease in the reaction temperature
- C. Increase in the concentration of X and Y
- D. Decrease in the concentration of X and Y
Question
Nitrogen(II) oxide reacts with hydrogen according to the equation below.
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
A suggested mechanism for this reaction is:
Step 1: NO + H2 ↔ X fast
Step 2: X + NO → Y + H2O slow
Step 3: Y + H2 → N2 + H2O fast
a.
Define the term rate of reaction.
[1]
b.
Explain why increasing the particle size of a solid reactant decreases the rate of reaction.
[2]
c.i.
Identify the rate-determining step.
[1]
A student hypothesized that the order of reaction with respect to H2 is 2.
Evaluate this hypothesis.
[1]
Question
The electron configuration of chromium can be expressed as [Ar]4s13d5.
Hydrogen and nitrogen(II) oxide react according to the following equation.
2H2(g) + 2NO(g) ↔ N2(g) + 2H2O(g)
At time t seconds, the rate of the reaction is
rate = k[H2(g)][NO(g)]2
When concentrated hydrochloric acid is added to a solution containing hydrated copper(II) ions, the colour of the solution changes from light blue to green. The equation for the reaction is:
[Cu(H2O)6]2+(aq) + 4Cl-(aq) → [CuCl4]2-(aq) + 6H2O(l)
a.i.
Explain what the square brackets around argon, [Ar], represent.
[1]
a.ii.
State the values of x and y.
[1]
Annotate the diagram below showing the 4s and 3d orbitals for a chromium atom using an arrow, ↑ and ↓, to represent a spinning electron.
[1]
b.i.
Explain precisely what the square brackets around nitrogen(II) oxide, [NO(g)], represent in this context.
[1]
b.ii.
Deduce the units for the rate constant k.
[1]
c.i.
Explain what the square brackets around the copper containing species represent.
[1]
c.ii.
Explain why the [Cu(H2O)6]2+ ion is coloured and why the [CuCl4]2- ion has a different colour.
[2]
d.
Some words used in chemistry can have a specific meaning which is different to their meaning in everyday English.
State what the term spontaneous means when used in a chemistry context.
[1]
Question
