4.5.1 Exothermic and endothermic reactions

Question 1

What is the conservation of energy principle?

Answer 1

Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place.

Question 2

What is an endothermic reaction? Give examples

Answer 2

A reaction where energy is taken in from surroundings so the surroundings temperature decreases - Thermal decomposition, reaction of citric acid and sodium hydrogencarbonate. Positive sign of energy change.

Question 3

What is an exothermic reaction. Give examples.

Answer 3

A reaction where energy is transferred
to the surroundings so that the surroundings temperature increases - combustion, oxidation reactions and neutralisation (acid + alkali) reactions. Negative signs of energy change.

Question 4

What is activation energy?

Answer 4

Minimum amount of energy that particles need to react.

Question 5

What is a reaction profile?

Answer 5

Reaction profile is a graph which shows the relative energies of reactants and product, as well as activation energy of the reaction.