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: Exothermic and Endothermic ReactionsHydrogen can be used to power vehicles in two ways: by burning it in a combustion engine, or by using it in a hydrogen fuel cell to produce electricity. In both cases the only product is water.
A car manufacturer is comparing a hydrogen fuel cell car with a conventional petrol car.
Evaluate the use of hydrogen fuel cells, compared with burning a fossil fuel such as petrol, as a way of powering vehicles. (6 marks)
Hydrogen reacts with chlorine to form hydrogen chloride:
H2+Cl2→2HCl
The table gives the bond energies needed.
| Bond | Bond energy / kJ mol⁻¹ |
|---|---|
| H–H | 436 |
| Cl–Cl | 242 |
| H–Cl | 431 |
(a) Calculate the overall energy change for this reaction. Show your working. (3 marks)
(b) State whether the reaction is exothermic or endothermic, and justify your answer using your value from part (a). (1 mark)
A student investigated the temperature change when sodium hydroxide solution was neutralised by hydrochloric acid. They measured the temperature of the acid, added the alkali, stirred, and recorded the highest temperature reached.
(a) State whether this neutralisation reaction is exothermic or endothermic, and give the observation that tells you this. (2 marks)
(b) Give one way the student could reduce heat loss to the surroundings during the experiment. (1 mark)
The diagram described below is a reaction profile for an exothermic reaction. The reactants start at a higher energy than the products. Between them is an "energy hump".
(a) Name the quantity represented by the height of the hump above the reactants' energy (the minimum energy needed for the reaction to occur). (1 mark)
(b) Explain how adding a catalyst would change this reaction profile, and how this affects the rate of reaction. (2 marks)
When ammonium nitrate dissolves in water in a beaker, the temperature of the water falls from 21 °C to 14 °C.
Explain, in terms of energy transfer, what type of change this is. (2 marks)
In a chemical reaction, energy must be supplied to break the bonds in the reactants.
State whether breaking chemical bonds is an exothermic or an endothermic process. (1 mark)