5.5.1.3 the energy change of reactions (ht only)

Question 1

What happen during a chemical reaction?

Answer 1

Energy is supplied to break bonds in the reactants and energy is released when bonds in the products are formed.

Question 2

How do you calculate the energy needed to brea bonds and the energy released when bonds are formed?

Answer 2

Bond energies.

Question 3

What are the steps for bond energies?

Answer 3

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

Question 4

In an exothermic reaction is the energy released greater or less than the energy needed to break existing bonds?

Answer 4

Greater.

Question 5

In an endothermic reaction is the energy needed to break existing bonds greater or less than the energy released from new formed bonds?

Answer 5

Greater.