Electrochemical cells and electrode potentials

Question 1

What does a more positive E tell you?

Answer 1

it is a stronger oxidising agent

Question 2

What does a more negative E tell you?

Answer 2

it is a stonger reducing agent

Question 3

What is the standard electrode potential?

Answer 3

the emf (V) measured when a half cell is connected to a standard hydrogen half-cell under standard conditions

Question 4

What is the role of the electrodes?

Answer 4

allows the flow of e-

Question 5

What electrode is used for gases and when there is no solid metals present? and why?

Answer 5

platinum electrode Pt
it is inert = unreactive

Question 6

How can you find the standard electrode potential of a reaction?

Answer 6

connect the half-cell containing the respective reaction to a standard hydrogen half cell

Question 7

In what direction do electrons flow in terms of the value of E?

Answer 7

e- flows to the reaction with the more positive standard E

from the negative electrode to the positive electrode

Question 8

What is the role of the salt bridge?

Answer 8

balances the charge of ions in the half-cells by allowing the controlled movement of ions between the two solutions

Question 9

What is electroplating?

Answer 9

plating an electrode in solid metal

Question 10

What need to be on a electochemical cell diagram?

Answer 10

the electrodes must be dipped in solution
salt bridge must be in solution and labelled
label the direction of e-
which electrode is recieving e- = positive and negative electrode labelled
standard conds
voltmeter reading

Question 11

What are the standard conditions?

Answer 11

1 atm
298K
1 moldm-3

Question 12

How is a salt bridge made?

Answer 12

a piece of filter paper soaked in potassium nitrate solution

Question 13

What is a potential difference?

Answer 13

the difference in energy between two points in a circuit

Question 14

At which electrode does reduction happen?

Answer 14

positive electrode

Question 15

At which electrode does oxidation happen?

Answer 15

the negative electrode

Question 16

At which electrode does oxidation happen?

Answer 16

the negative electrode

Question 17

What is the standard cell potential?

Answer 17

the difference between standard E values

Question 18

What does a more positive standard E value tell you?

Answer 18

the more likely that half equation will run forwards in the direction of reduction (e- gained)

Question 19

What will happen if you increase the concentration of reactants on the left of the reaction? and what will this do to the standard E value?

Answer 19

the equilibrium will shift to the right - so reduction is more favoured and the standard electron potential will become more positive

Question 20

What are the 2 limiting factors of standard electrode potential values?

Answer 20

not under standard conds
rates of reaction

Question 21

How does a high activation energy affect the standard electrode potential?

Answer 21

high Ea may prevent a reaction from happening or making it very slow, therefore it may not reach equilibrium
standard E values are only a prediction of what could happen

Question 22

What is a storage cell?

Answer 22

an electrochemical cell where the voltmeter is replaced by an electrically powered device

Question 23

How can a cell be recharged?

Answer 23

possing a current through the cell in the opposite direction to the normal current = drives reactions in reverse and regenerated the reactants

Question 24

What is a fuel cell?

Answer 24

an electrochemical cell which used the energy released by reaction of fuel with oxygen to generate a voltage

Question 25

What is the cell potential of a hydrogen-oxygen fuel cell?

Answer 25

1.23 V

Question 26

What is the overall reactio for a hydrogen-oxygen fuel cell?

Answer 26

H2 + 1/2 O2 –> H2O

Question 27

Is the second electron affinity of oxygen exothermic or endothermic?

Answer 27

endothermic = requires energy to add a second electron to an already negatively charged oxygen ion O-

Question 28

Which type of reaction has electrons on the left side?

Answer 28

reduction