Energy Changes

Question 1

Exothermic reactions

Answer 1

Transfers energy to the surroundings, so the temperature of the surroundings increase

Question 2

Examples of exothermic reaction

Answer 2

Combustion, respiration, neutralisation

Question 3

Endothermic reactions

Answer 3

Takes in energy from the surroundings, so the temperature of the surroundings decrease

Question 4

Examples of endothermic reaction

Answer 4

Thermal decomposition, photosynthesis

Question 5

Temperature change practical

Answer 5

Place the polystyrene cup inside the glass beaker to make it more stable

Measure an appropriate volume of the solution, eg 25 cm3

Measure an appropriate mass of the solid, or select a suitable-sized piece of metal

Place the solution in a polystyrene cup and record the temperature of the solution

Record the highest and lowest temperature

Question 6

Activation energy

Answer 6

The minimum amount of energy required for a chemical reaction to occur

Question 7

Electrochemical cells

Answer 7

Non-rechargeable -

Cheap, only used once, creates a lot of chemical pollution

Rechargeable -

Expensive, used many times, creates less chemical pollution

Question 8

Non-rechargeable cells

Answer 8

Chemical reactions stop when one of the reactants has been used up

E.g. alkaline batteries

Question 9

Rechargeable cells

Answer 9

Chemical reactions are reversed when an external electrical current is supplied making it rechargeable

Question 10

Fuel cells

Answer 10

Converts chemical energy into electrical energy in an open system

Question 11

Hydrogen fuel cells

Answer 11

Used in spacecraft, creates CO2

Question 12

Bond energy formula

Answer 12

Energy required to break - energy required to make

Exothermic reaction = -ve

Endothermic reaction = +ve