Energy Changes

Question 1

Activation Energy

Answer 1

Minimum energy needed to start a reaction.

Overcoming repulsive force so they collide with enough energy for the reaction to occur

Question 2

Exothermic

Answer 2

Exothermic - gives out thermal energy to the surroundings

Question 3

Endothermic

Answer 3

Endothermic - takes in thermal energy from the surroundings

Question 4

bond breaking =

Answer 4

endothermic

Question 5

bond making =

Answer 5

exothermic

Question 6

energy change in the reaction =

Answer 6

bond energies of reactants - bond energies of products

Question 7

exothermic means there is

Answer 7

a negative answer

Question 8

endothermic means there is

Answer 8

a positive answer

Question 9

a battery

Answer 9

more than one cell connected together

Question 10

a cell

Answer 10

a device containing electrons immersed in an electrolyte

Question 11

Chemical Cells

Answer 11

use a chemical reaction to transfer energy by electricity

Question 12

Simple Cells

Answer 12

can be made by connecting two different metals in contact with an electrolyte

Question 13

Primary Cells

Answer 13

cannot be recharged - once all chemicals have been reacted the cell must be replaced

Question 14

Secondary Cells

Answer 14

are rechargeable - a charger passes an electric current through the cell to reverse the reaction. This regenerates original chemicals to start again

Question 15

Fuel Cells

Answer 15

produce a voltage continuously as long as they are supplied with :

• a constant supply
• oxygen e.g. from the air

Question 16

What happens to the fuel in fuel cells

Answer 16

• electrochemically oxidised rather than being burned
• reaction takes place at a lower temperature
• energy is released as electrical energy not thermal energy

Question 17

Alkaline Cell

Answer 17

• cheaper to manufacture

- may end up in landfill sites once fully discharged ; recyclable though its expensive

Question 18

Rechargeable Cell

Answer 18

• can be recharged many times before being recycled , reducing the use of resources
• costs more to manufacture

Question 19

Hydrogen Fuel Cell

Answer 19

• easy to maintain
• small size
• water is the only chemical product
• very expensive to manufacture
• need a constant supply of hydrogen fuel which is a flammable gas