C7

Question 1

which would have a larger potential difference:
a cell containing magnesium and copper
or
a cell containing zinc and tin

Answer 1

magnesium and copper- because there is a greater difference in reactivity

Question 2

making bonds is:

Answer 2

exothermic

Question 3

breaking bonds is:

Answer 3

endothermic

Question 4

what is an electrolyte?

Answer 4

A solution that can conduct electricity

Question 5

Why do cells only produce electricity for a set time?

Answer 5

Eventually the chemicals will be used up and the reaction will stop

Question 6

Greater difference in reactivity between the electrodes =

Answer 6

greater potential difference

Question 7

How comes some batteries are rechargeable?

Answer 7

The chemical reactions can be reversed

Question 8

Fuel cells: negative electrode =

Answer 8

2H2 –> 4H+ + 4e-

Question 9

Fuel cells: positive electrode =

Answer 9

O2 + 4H+ + 4e- —> 2H2O

Question 10

Fuel cells: overall equation

Answer 10

2H2 +O2 —> 2H2O

Question 11

compare hydrogen fuel cells and rechargeable batteries in terms of working/ energy being provided

Answer 11

HFC- will provide electricity as long as hydrogen is provided
RB- will run out and need to be recharged

Question 12

compare hydrogen fuel cells and rechargeable batteries in terms of- efficiency

Answer 12

HFC- doesn’t become any less efficient
RB- store less electricity the more they’re charged so will need replacing

Question 13

compare hydrogen fuel cells and rechargeable batteries in terms of: products

Answer 13

HFC - produces drinkable water

Question 14

compare hydrogen fuel cells and rechargeable batteries in terms of: safety

Answer 14

HFC - Hydrogen is highly flammable and explosive
RB - no dangerous fuels, though can catch fire if manufactured incorrectly

Question 15

compare hydrogen fuel cells and rechargeable batteries in terms of: potential difference

Answer 15

HFC - low p.d produced so several needed
RB- produces a greater pd

Question 16

Law of conservation of energy

Answer 16

Energy is conserved

Question 17

Exothermic

Answer 17

• gives out energy
• temperature of surroundings increases
• energy in bonds of reactants will be HIGHER than energy in bonds of products

Question 18

Endothermic

Answer 18

• takes in energy
• temperature of surroundings decreases
• energy of bonds of reactants is LOWER than energy of bonds of products

Question 19

Exothermic reaction profile–

Answer 19

Product lower than reactants

Question 20

Endothermic reaction profile–

Answer 20

Product energy higher than reactant

Question 21

Activation energy on reaction profile

Answer 21

Arrow from reactants to top of curve

Question 22

Overall energy change on reaction profile

Answer 22

Arrow from reactants to products (points down on exothermic, up on endothermic)

Question 23

Endothermic reaction, energy from ___ bonds is bigger

Answer 23

Breaking

Question 24

Exothermic reaction, energy from ___ bonds is bigger

Answer 24

Making

Question 25

Cells are made from

Answer 25

Two different metals and electrolyte

Question 26

In cells, electrons flow from one metal to the other to produce electric current. Why?

Answer 26

They are different metals

Question 27

Bigger difference in reactivity between the two metals in the cell,

Answer 27

Bigger voltage produced

Question 28

A battery is made of?

Answer 28

Two or more cells in series which increases the potential difference

Question 29

Alkaline batteries can be used how many times?

Answer 29

Once

Question 30

Rechargeable batteries can be recharged. Why?

Answer 30

Charging the battery reverses the chemical process

Question 31

A fuel cell is provided with...

Answer 31

Fuel [hydrogen] Air//oxygen

Question 32

Fuel is oxidised electrochemically to produce...

Answer 32

Potential difference

Question 33

Benefits of fuel cell over a combustion engine(petrol)

Answer 33

1. Doesn't release thermal energy as waste 2. Only product is water rather than many harmful gases

Question 34

Fuel cell half equation: negative electrode

Answer 34

2H2 + 4OH- ---> 4H2O + 4e-

Question 35

Fuel cell half equation: positive electrode

Answer 35

O2 + 2H2O + 4e- --> 4OH-

Question 36

Fuel cell half equation: ultimately

Answer 36

2H2(g) + O2(g) --> 2H2O(l)