6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Learn this properly: Rate of Reaction — Measuring and CalculatingA student investigated the reaction between marble chips (calcium carbonate) and dilute hydrochloric acid, which produces carbon dioxide gas:
CaCO3+2HCl→CaCl2+H2O+CO2
They found the reaction went faster when they (i) increased the temperature of the acid, (ii) increased the concentration of the acid, and (iii) used the same mass of marble as a powder instead of large chips.
Explain, using collision theory, why each of these three changes increased the rate of reaction. (6 marks)
Hydrogen reacts with chlorine to form hydrogen chloride:
H2+Cl2→2HCl
The table gives the bond energies.
| Bond | Bond energy / kJ mol⁻¹ |
|---|---|
| H–H | 436 |
| Cl–Cl | 242 |
| H–Cl | 431 |
(a) Calculate the energy needed to break all the bonds in the reactants. (1 mark)
(b) Calculate the overall energy change (ΔH) for this reaction, and state whether it is exothermic or endothermic. Show your working. (3 marks)
A catalyst is used to speed up many industrial reactions. A catalyst is not used up in the reaction.
(a) Explain, in terms of activation energy, how a catalyst increases the rate of a reaction. (2 marks)
(b) State one economic reason why using a catalyst is beneficial in industry. (1 mark)
A student measured the volume of gas produced over time in a reaction between magnesium and dilute hydrochloric acid. The results are shown below.
| Time / s | 0 | 20 | 40 | 60 | 80 | 100 |
|---|---|---|---|---|---|---|
| Volume of gas / cm³ | 0 | 28 | 46 | 54 | 56 | 56 |
(a) Calculate the mean rate of reaction over the first 40 seconds, in cm³/s. Show your working. (2 marks)
(b) State and explain what the data between 80 s and 100 s tell you about the reaction. (1 mark)
When ammonium chloride is dissolved in water, the temperature of the solution falls. This is an endothermic change.
Explain, in terms of energy transfer with the surroundings, why the temperature of the solution falls during an endothermic change. (2 marks)
In a reaction profile diagram for an exothermic reaction, the products are drawn at a lower energy than the reactants.
State what the difference in energy between the reactants and the products represents in an exothermic reaction. (1 mark)