Aqa Chemistry Unit 5 - Electrochemical Cells

Front 1

What are electrochemical cells made up of?

Back 1

Made from two different metals dipped in salt solution s of their own ions and connected by a wire

Front 2

What type of reaction happens within a electrochemical cell

Back 2

Redox reaction as it invovles both oxidation and reduction

Front 3

How does electrons move between electrochemical cells

Back 3

The more reactive cell (more easily looses its electrons) is oxidised and the elctrons flow through the circuit (producing a voltage that a meter can read) to the other cell reducing that cell.q

Front 4

What are the electrodes made out of and why

Back 4

platinum as it is an inert metal

Front 5

How do you calculate cell potential

Back 5

cell potential = right hand side - left hand side

(conventional drawing of half cells

Front 6

What conditions will affect electrode potentials and how is this prevented

Back 6

A change in temperature, pressure or concentration will affect the electrode potential due to changing the equilibrium of the reaction. So standard conditions are always used to prevent this change

Front 7

A negative electrode potential means the half cell is easier or harder to oxidise

Back 7

Easier to oxidise

Front 8

A positive elctrode potential means the half cell is easier or harder to oxidise

Back 8

Harder to oxidise

Front 9

What is the standard electrode potential definition

Back 9

The standard electrode potential of a half-cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

Front 10

What voltage does standard hydrogen half-cell give

Back 10

0.00 V

Front 11

If a metal is more reactive what are the properties of the electrons

Back 11

A more reactive metal will lose it's electrons more easily to form a positive ion

Front 12

If a non-metal is more reactive what are the properties of the electrons

Back 12

A more reactive non-metal will more readily accept electrons to for a negative ion

Front 13

What type of reaction does non-rechargeable cells use

Back 13

Irreversible reactions

Front 14

What type of reaction does rechargeable cells use

Back 14

Reversible reactions

Front 15

What is a common type of non-rechargeable cell

Back 15

Dry alkaline battery

Front 16

Why is it not practical to reverse the reaction in a dry alkaline battery and what are the dangers

Back 16

Under the right conditions they can be reversed but they may leak or explode

Front 17

Why do dry alkaline batteries leak or explode when the reaction is reversed

Back 17

The zinc anode which forms the casing of the battery is oxidised and so becomes thinner

Front 18

What reasons other than the oxidising of an anode are there for why a non-rechargeable

Back 18

The ammonium ions produce hydrogen gas which is lost. The hydrogen gas is needed to reform the ammonium ions and so the as the hydrogen gas is lost it cannot be recharged

Front 19

How are batteries recharged

Back 19

By applying a current to force the electrons to flow in the opposite direction and reverse the reaction

Front 20

Why is it possible for batteries to be recharged

Back 20

None of the substances needed have been used up such as the hydrogen gas to reform the ammonium ions

Front 21

How do fuel cells generate electricity

Back 21

They use hydrogen and oxygen

Front 22

How are hydrogen and oxygen separated in a fuel cell

Back 22

Hydrogen and oxygen are in separate platinum-containing electrodes with an ion-exchange membrane towards the positive electrode

Front 23

What does the ion-exchange membrane do in a fuel cell

Back 23

It only allows H+ ions and prevents electrons from going through separating the electrodes