C3.2

Question 1

What is an exothermic reaction?

Answer 1

Energy is released to the surroundings
When the temperature of the surroundings increase during a chemical reaction
E.g. combustion, neutralisation

Question 2

What is an endothermic reaction?

Answer 2

Temperature of the surroundings decreases
Absorbs heat from the surroundings
E.g. photosynthesis, ice pack

Question 3

Is breaking bonds endothermic or exothermic?

Answer 3

Energy is transferred from the surroundings
Endothermic

Question 4

Is making bonds endothermic or exothermic?

Answer 4

Energy is transferred to the surroundings
Exothermic

Question 5

What is activation energy?

Answer 5

Minimum energy needed for a reaction to start
Breaks bonds in the reactants

Question 6

What is the reaction profile like for an endothermic reaction?

Answer 6

Energy transferred to break the bonds is higher than the energy to make the bonds
Energy change is positive
BREAK - MAKE = POSITIVE
Graph:
- upward energy change arrow
- reactants and lower than products

Question 7

What is the reaction profile like for an exothermic reaction?

Answer 7

Energy transferred to make the bonds is higher than the energy to break the bonds
Energy change is negative
BREAK - MAKE = NEGATIVE
Graph:
- downward energy change arrow
- reactants higher than products

Question 8

What is bond energy?

Answer 8

The energy needed to break 1 mole of a particular bond

Question 9

How do you calculate the energy change of a reaction?

Answer 9

1) work out the bond energy for the reactant side (BREAK)
2) work out the bond energy of the products side (MAKE)
3) use the formula BREAK - MAKE = energy change
4) if the sign is negative then it is an exothermic reaction, if positive it is an endothermic