Chemical Reactions and Energy

Question 1

What is an exothermic reaction?

Answer 1

Reactions that transfer energy to the surrounding. The energy is usually transferred as head energy, causing the reaction mixture and it’s surrounding to become hotter.

Question 2

What are some examples of an exothermic reaction?

Answer 2

• Combustion (burning)

- The reaction between water and calcium oxide

Question 3

What is an endothermic reaction?

Answer 3

Reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and it’s surroundings to become colder.

Question 4

What are some examples of endothermic reactions

Answer 4

• Electrolysis

- Thermal decomposition of calcium carbonate in a blast furnace

Question 5

Describe the reactants in an exothermic energy diagram

Answer 5

in exothermic reactions the reactants are higher than the products

Question 6

Describe the reactants in an endothermic energy diagram

Answer 6

in endothermic reactions the reactants are lower than the products

Question 7

What is activation energy

Answer 7

The activation energy is the minimum amount of energy required for a reaction to take place.

This can be represented on the energy profile as a ‘hump’. This shows how much energy is needed for the reactants to react and become products.

Question 8

How do you calculate bond energy?

Answer 8

1. Add together the bond energies for all the bonds in the reactants – this is the ‘energy in’.
2. Add together the bond energies for all the bonds in the products – this is the ‘energy out’.
3. Calculate the energy change = energy in – energy out