IB Docs (2) Team MC test: Collision theory & rates of reaction
Multiple choice test on 6.1 Collision theory & rates of reaction
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Which is a correct unit for rate of reaction?
Rate of reaction is equal to change in concentration of a reactant or product per unit time
Which practical methods can be used to follow the rate of a chemical reaction?
I. measure the conductivity
II. measure the absorption at a particular wavelength
III. measure the pH
If there is a change in the amount of ions in solution during the reaction conductivity can be used. pH can be used if there is a change in acidity and if there is a change in colour the change in absorption at a particular wavelength can be followed.
The graph shows the volume of carbon dioxide evolved over time when an acid is added to a metal carbonate.
Which are correct statements
I. The rate at time t = Δt ÷ ΔV
II. The initial rate is greater than the rate at time t.
III. The reaction is nearing completion at time t.
The concentration of the acid is greater at the start so the initial rate is greater (shown by the slope of the graph) at time t the slope is close to becoming horizontal so the reaction is near completion. The rate at time t is equal to the gradient of the slope = ΔV ÷ Δt.
Which will considerably increase the initial rate of the reaction between hydrochloric acid and excess solid calcium carbonate?
The CaCO3 is in excess so doubling the amount will have little effect (it may increase slightly as the surface area has increased slightly). Doubling the size of the CaCO3 reduces the surface area so decreases the rate of reaction. Increasing the concentration of the acid means more collisions will occur leading to a significantly increased rate.
The graph shows the Maxwell-Boltzmann curve for the distribution of the kinetic energies of reactant particles at two different temperatures.
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Which is a correct statement about the graph?
The area under the curves is equal to the total number of particles present so does not change. x and y are the average kinetic energy of the particles at the respective temperatures. T2 > T1 and the value of Ea remains constant (although more particles will possess this minimum energy required to react at a higher temperature).
According to collision theory what must be true for a reaction to occur when two reactant particles collide ?
The energy of the collision must be equal to or greater than the activation energy and the particles must collide with the proper orientation in order for the particles to react.
Which is a correct statement about a suitable catalyst for a a specified chemical reaction?
Catalyst may change chemically during the reaction but not permanently by the end of the reaction. Catalyst do not lower the activation energy of the specified reaction but they work by providing an alternative pathway with a lower activation energy.
The concentrations of reactants and products during the reaction P + 2Q → 2S are shown in the table
| [P] / mol dm−3 | [Q] / mol dm−3 | [S] / mol dm−3 | |
| Initial | 3 | 4 | 0 |
| After 20 seconds | 2 | 2 | 2 |
Which is a correct statement about the rate of the reaction?
With reference to P and Q the rate must be negative as the concentrations of P and Q are decreasing. A change of 2 mol dm−3 over 20 s in the concentration of S gives a rate of 0.1 mol dm−3 s−1.
The graph shows the reaction profile for the hydrogenation of ethene using a nickel catalyst.
Which row contains the corrects descriptions for x, y and z?
| Row | x | y | z |
| 1 | Ea (uncatalysed) | Ea(catalysed) | ΔH(exothermic reaction) |
| 2 | Ea(catalysed) | Ea (uncatalysed) | ΔH(exothermic reaction) |
| 3 | Ea (uncatalysed) | Ea(catalysed) | ΔH(endothermic reaction) |
| 4 | Ea(catalysed) | Ea (uncatalysed) | ΔH(endothermic reaction) |
The products are more stable so it is an exothermic reaction and the catalysed alternative pathway has the lower activation energy compared to the uncatalysed reaction.
Which factors directly explain why the rate of a reaction increases when the temperature is increased?
I. More of the reacting particles will possess the necessary activation energy.
II. The frequency of the collisions increases.
III. The value of the average kinetic energy of the particles increases
The average kinetic energy of the particles does increase but that in itself does not explain why the reaction rate increases as the higher average kinetic energy is likely to still be less than the activation energy. Although increasing the temperature does cause an increase in the collision rate many of the collisions still do not result in a reaction so although frequency is a minor explanation the major explanation is that more particles will possess the activation energy.
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