Cells and Batteries and Fuel cells

Question 1

Describe how we can produce electricity with 2 metals

Answer 1

If we take two different metals and place them into an electrolyte then we can produce electricity

Question 2

What is an electrolyte

Answer 2

A solution that can conduct electricity - e.g. a solution for an ionic compound

Question 3

what is a cell

Answer 3

A simple cell can be made by connecting two different metals in
contact with an electrolyte.

Question 4

what is a battery

Answer 4

Batteries consist of two or more cells connected together in series
to provide a greater voltage

Question 5

Facts about cell

Answer 5

Cells can only produce electricity for a certain period of time
Eventually the chemicals in the cell run out and the reaction stops

Cells only produce electricity if we use metals with different reactivities

Question 6

What does the size of the potential difference depend on

Answer 6

The size of the potential difference depends on the difference in the reactivity between the two metals

The greater the difference between the reactivity of the metals, the greater the potential difference produced by the cell

the electrolyte also affects the potential difference

Question 7

Describe the potential differences of cells containing mg and cu and a cell containing zn and sn

Answer 7

A cell containing mg and cu will have a large potential difference as there is a large difference in reactivity between the two metals

a cell containing zn and sn will have a smaller potential difference as there is a smaller difference in reactivity between the two metals

Question 8

describe non rechargeable bateries

Answer 8

chemicals inside produce electricity

when chemicals get used up (at some point)/reactants in the batteries run out, the battery goes flat (the voltage drops to zero) and no more electricity is produced

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

there is no way that we can reverse these reactions, so these are non-rechargeable batteries

Question 9

Explain why rechargeable batteries can be recharged

Answer 9

We can reverse the chemical reactions when we apply an electrical current

Question 10

Which metal is at the negative electrode

Answer 10

The more reactive metal has a greater tendency to lose electrons so is the negative electrode (negative since the charge builds up)

Question 11

in an electrochemical cell, the anode is the _____ and the cathode is the _________-

Answer 11

anode - negative electrode
cathode - positive electrode

Question 12

what would be the voltage of an electrochemical cell where both electrode are made of the same metal

Answer 12

0V - no difference in reactivity

Same reactivity so both have the same tendency to lose electrons / no difference in potential/reactivity

Question 13

in both electrochemical cells and electrolysis, how is current carried though

the wires
the electrolyte

Answer 13

the wires - delocalised electrons
the electrolyte - mobile ions

Question 14

why are some metals more reactive than others

Answer 14

reactive metals tend to lose electrons more easily (form positive ions)

Question 15

Zn + Cu = 0.78V
Pb + Cu = 0.22 V
What is voltage between Zn and Pb

Answer 15

0.78 - 0.22 = 0.56 v (larger value - smaller value

Question 16

if it wired correctly, how should the arrangement be

Answer 16

If it is wired correctly, the most reactive metal should always be the negative electrode and the cell voltage should always be positive

Question 17

what are fuel cells

Answer 17

Fuel cells are supplied by an external source of fuel (eg hydrogen) and oxygen or air

Question 18

in fuel cells - what electrode is the anode

Answer 18

negative electrode

Question 19

in fuel cells what electrode is the cathode

Answer 19

positive electrode

Question 20

write down the half equations for the reactions at the NEGATIVE ELECTRODE, in the hydrogen fuel cell

Answer 20

2H2 –> 4H+ + 4e-

2H2 forms 4H+ + 4e-
These electrons now pass through the wire and that is our electrical current

Question 21

write down the half equations for the reactions at the POSITIVE ELECTRODE , in the hydrogen fuel cell

Answer 21

O2 + 4H+ + 4e - —-> 2H2O

At positive electrode, oxygen molecules combine with the hydrogen ions and electrons (produced at the negative electrode)

Water is the product

Question 22

Overall equation for hydrogen fuel cell

Answer 22

2H2 + O2 —> 2H2O
In the hydrogen fuel cell, hydrogen is combining with oxygen (hydrogen is being oxidised)

Question 23

how hydrogen fuel cells work

Answer 23

Hydrogen fuel cells use two simple gases, hydrogen and oxygen to produce electricity and the only waste product is water

Question 24

Advantages of hydrogen fuel cells compared to rechargeable batteries

Answer 24

hydrogen fuel cells will produce electricity for as long as you provide hydrogen
Rechargeable batteries run out and need to be recharged

Hydrogen fuel cells do not get less efficient the longer they run
Rechargeable batteries store less electricity, the more charging cycles they go through and eventually need to be replaced

Hydrogen fuel cells can be a source of drinkable water e.g. for astronauts on a space-craft

Question 25

Disadvantages of hydrogen fuel cells compared to rechargeable batteries

Answer 25

Hydrogen fuel cells run on hydrogen which is an explosive gas and is very difficult to store safely

No dangerous fuels are required with rechargeable batteries
Some types of rechargeable batteries can catch fire if not manufactured correctly

Hydrogen fuel cells produce a relatively low potential difference or voltage so several are needed together

Rechargeable batteries can produce a greater potential difference than a hydrogen fuel cell