11. Electrode Potentials and Electrochemical Cells Flashcards Preview

AQA A Level Physical Chemistry > 11. Electrode Potentials and Electrochemical Cells > Flashcards

Flashcards in 11. Electrode Potentials and Electrochemical Cells Deck (140)
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1

What is a redox reaction?

In a reaction if an element is oxidised then another must be reduced

2

What happens when a piece of metal is dipped into a solution of its metal ions?

An equilibrium is set up and there is a tendency

• for the metal to form positive ions and go into solution

• as well as for the metal ions in solution to gain electrons and form metal

3

What is a half cell?

When a piece of metal is dipped into a solution of its metal ions and an equilibrium is set up

4

What two things can happen when a piece of metal is dipped into a solution of its metal ions and an equilibrium is set?

• tendency for the metal to form positive ions and go into solution

• tendency for the metal ions in solution to gain electrons and form metal

5

What is an electrode also known as?

A half cell

6

For a zinc rod immersed in Zn²⁺ ion solution, what could happen?

• each Zn on rod could deposit two electrons on the rod and move into solution as Zn²⁺ ions (-ve charge on rod)

• Zn²⁺ ions in solution could accept 2 electrons and move onto rod to become Zn atoms (+ve charge on rod)

7

What happens when a zinc rod is immersed in Zn²⁺ ion solution and electrons are transferred?

A potential difference is set up between the rod and the solution

8

What is an electrode potential?

When a metal is dipped in a solution of its metal ions and a potential difference is set up between the rod and the solution

9

When will the potential difference of a half cell be greater?

When there is a greater tendency to give up electrons (forming ions)

10

What does an electrode potential indicate?

How readily the metal gives up electrons

11

Does a chemical reaction take place in a lone half cell?

No - there is simply a potential difference between the rod and solution

12

What does the potential difference in a half cell depend on?

• nature of the ions in solution

• concentration of ions in solution

• type of electrode used

• temperature

13

What is required in a half cell where there is no solid metal involved in the half equation?

A metal electrode

14

Why is a metal electrode required in a half cell where there is no solid metal involved?

To allow the flow of electrons

15

When a half cell involves no solid metal, what metal is usually used as the electrode?

Platinum (Pt)

16

Why is platinum used for metal electrodes?

It is unreactive/inert

17

What are some types of electrodes?

• gas electrodes

• redox electrodes

18

What is a gas electrode?

A gas and a solution of its ions

19

What is a redox electrode?

Two different ions of the same element present in solution

20

Can the potential of a half cell be measured directly?

No

21

What letter represents the potential of a cell?

E

22

How is the potential of a half cell measured?

Connected to another half-cell of known potential, and p.d. between the two half cells is measured

23

What is an electrochemical cell?

When two half cells are combined

24

What is formed when two half cells are combined?

An electrochemical cell

25

Are the two half reactions that make up a cell in equilibria?

Yes

26

What is the position of equilibria affected by?

• temperature

• concentration

• pressure

27

When can cell potentials only be compared?

Under standard conditions

28

Why must cell potentials be compared under standard conditions?

Different conditions could change the position of equilibrium

29

What are the standard conditions that cell potentials are measured under?

• 298K

• 1 moldm⁻³ solution of ions

• 100 kPa

30

How is the full potential difference (emf) of cells measured?

Under zero-current conditions