Worksheet 7.
1
Thermochemistry
1 In an exothermic reaction, energy is ‘given out’ (i.e. transferred) to the surroundings.
In an endothermic reaction, energy is ‘taken in’ from the surroundings.
Consider these graphs (A and B) showing the temperature change in two different experiments.
50 Graph A
40
Temperature / °C
30
20
10
0
Time
20 Graph B
15
Temperature / °C
10
0
Time
a Does graph A show an endothermic or an exothermic reaction? Explain your answer.
b Does graph B show an endothermic or an exothermic reaction? Explain your answer.
c Which of the following changes or chemical reactions are exothermic and which are endothermic?
i a candle burning:
ii ammonium chloride dissolving, producing a decrease in temperature:
iii dynamite exploding:
iv respiration:
v photosynthesis
© Cambridge University Press 2014 IGCSE® Chemistry Worksheet 7.1 1
2 The following is an energy level diagram for the reaction between ethanol and oxygen.
ethanol + oxygen
Energy
1367 kJ / mol
carbon dioxide
+ water
Course of reaction
Draw energy diagrams for the following two reactions.
a 6CO2 + 6H2O → C6H12O6 + 6O2 ΔH = +2880 kJ/mol
b H2 + I2 → 2HI ΔH = +53 kJ/mol
3 a In any chemical reaction, energy must first be supplied in order to make the chemical reaction start to
happen. How is this energy used to start the reaction?
b During a chemical reaction some energy is released. What is happening to cause this energy to be released?
c What is happening to the balance of these energy changes in:
i an exothermic reaction?
ii an endothermic reaction?
© Cambridge University Press 2014 IGCSE® Chemistry Worksheet 7.1 2
