C6 energy changes in chemical reactions

Question 1

What do the terms exothermic and
endothermic mean?

Answer 1

Endothermic - a reaction that takes in
heat energy from the surroundings.
Exothermic - a reaction that gives out
energy to the surroundings.

Question 2

Give an example of a type of reaction
that is exothermic

Answer 2

Combustion
Neutralisation

Question 3

Give an example of an endothermic
reaction

Answer 3

Thermal decomposition
Photosynthesis

Question 4

In terms of bond energies, what happens
during a chemical reaction?

Answer 4

Energy is needed to break bonds and is released when bonds are made.
Exothermic: Energy released from making bonds is greater than the energy
used to break bonds.
Endothermic: Energy required to break bond is greater than the energy
released when making bonds.

Question 5

What is a reaction profile?

Answer 5

A graph which shows the relative
energies of reactants and products, as
well as the activation energy of the
reaction.

Question 6

How can the energy change of a reaction
be calculated from bond energies?

Answer 6

Energy change (kJ mol-1) =
Total energy of bonds broken - total energy of bonds made

Question 7

If the energy change of a reaction is
negative, is the reaction exothermic or
endothermic?

Answer 7

Exothermic
Energy has been lost to the surroundings

Question 8

Fill in the gap: ‘Fuels are burned to
release ____ ____’

Answer 8

Heat energy

Question 9

Which colourless gas can be used as a
fuel?

Answer 9

Hydrogen