C5 - Energy Changes

Question 1

What are two things about exotérmica reactions? What are examples of some?

Answer 1

1. Breaking bonds takes leas energy than energy released when bonds form.
2. Heat energy exits the reaction to surroundings and the surroundings gain energy = temperature increase.
3. Combustion and neutralisation

Question 2

What are two things about endothermic reactions? What are examples of them?

Answer 2

1. Breaking bonds takes more energy than energy released when bonds form.
2. Heat energy enters the reaction from surroundings so surroundings have less energy = Temperature decrease.
3. Thermal decomposition and sport injury packs.

Question 3

What is the energy change calculation?

Answer 3

Energy = reactant bonds broken - product bonds made

Question 4

What does it mean if the energy after the calculation is negative or positive?

Answer 4

Negative = exothermic
Positive = endothermic

Question 5

Required practical.

Answer 5

1. Thermometer - take start and end temp
2. Polystyrene cup - reduce heat loss to surroundings
3. Chemical 1 - acid
4. Chemical 2 - metal
5. Eg. Independent - change metalx5
   Dependent - measure temp of acid before and after
   Control - mass of metal, concentration and volume of acid
   Stir constantly (random error
6. Draw a graph
7. Temp increase until… b/c reaction exothermic, temp becomes constant because limiting reactants run out.

Question 6

Draw endo and exo graphs.