A student compares the reaction profiles for three reactions, A, B and C.
The table shows the energy of the reactants, the energy at the highest point of each reaction profile and the energy of the products.
| Reaction | Energy of reactants (kJ) | Energy at highest point (kJ) | Energy of products (kJ) |
|---|---|---|---|
| A | 200 | 320 | 50 |
| B | 200 | 240 | 130 |
| C | 200 | 380 | 290 |
Which reaction is endothermic?
Give a reason for your answer.
Calculate the activation energy for reaction A.
Activation energy = ...... kJ
Calculate the energy given out by reaction A.
Energy given out = ...... kJ
Describe what the reaction profile for reaction C looks like.
Include where the arrows for the activation energy and for the overall energy change should be drawn.
The student says:
"The reaction that gives out the most energy always has the smallest activation energy."
Evaluate the student's statement. Use the data in the table.
At room temperature, reaction B starts on its own. Reaction A only starts when it is heated.
Explain why. Use the data in the table.
51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.