C20 - Electrochemical cells

Question 1

How is the emf of an electrochemical cell calculated?

Answer 1

Flip the most negative value, add the 2 numbers

Question 2

What does a negative overall emf mean for the feasibility of the reaction?

Answer 2

It is infeasible

Question 3

How do you write cell diagrams?

Answer 3

Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
Lines represent a phase line, change of state or to aq
2 lines represent a barrier between half cells

Question 4

What happens in a cell diagram if there is no phase change?

Answer 4

a comma is used e.g.
Zn(s) | Zn2+(aq) || Fe3+(aq), Fe2+(aq) | Pt(s)
Pt is the unreactive electrode as there are no metals on right hand side

Question 5

What are the requirements for a hydrogen cell with an emf of 0

Answer 5

1.0 mol dm-3 of HCl
Standard conditions

Question 6

What is the half equation at the negative electrode of a lithium battery?

Answer 6

Li (s) → Li+(s) + e–

Question 7

What is the half equation at the positive electrode of a lithium battery?

Answer 7

Li+(s) + CoO2(s) +e–→ Li+(CoO2)–(s)

Question 8

What is the half equation at the negative electrode of a hydrogen battery?

Answer 8

2H2(g) + 4OH–(aq) → 4H2O (l)+ 4e–

Question 9

What is the half equation at the positive electrode of a hydrogen battery?

Answer 9

O2(g) +2H2O + 4e–→ 4OH–(aq)

Question 10

What happens at the negative electrode in electrochemical cells?

Answer 10

Oxidation

Question 11

What happens at the positive electrode in electrochemical cells?

Answer 11

Reduction