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Physical Chemistry Year 2 > Electrochemical Cells > Flashcards

Flashcards in Electrochemical Cells Deck (28)
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1

What happens when a rod of a metal is dipped into a solution of its own ions

An equilibrium is set up between the solid metal and the aqueous metal ions

2

Write a half equation for zinc(s) to zinc (II)

Zn(s) <=> Zn2+(aq) +2e-

3

What is the simplest salt bridge made of

Filter paper soaked in saturated solution of KNO3

4

Why are salt bridges necessary

They complete the circuit, but avoid further metal/ion potentials as does not perform electrochemistry
Allows ion movement to balance the charge. Do not react with electrodes

5

What symbol is used to represent a salt bridge In standard notation

II

6

What type of species goes on the outside in standard cell notation

The most reduced species

7

What does I indicate

Phase boundary

8

What happens at the left side electrode

Is where oxidation occurs
Half cell with mist negative E nought value

9

What happens at the right hand electrode

Reduction occurs
Half cell with most positive E nought value

10

What conditions is the SHE used in

Temperature = 298 K
Pressure = 100 kPa
[H+] = 1.00 mil dm-3

11

What is SHE used for

Comparing other cells against
E nought value is 0

12

Why might you use other standard electrodes occasionally

Cheaper
Easier
Quicker
Platinum is expensive

13

What factors will change E nought values

Concentration of ions
Temperature

14

What happens if you reduce the concentration of the ions in the left hand side cell

Equilibrium moves to the left to oppose the change
This release more electrons
So E nought value becomes more negative
So EMF increases

15

How do you calculate the EMF of a cell from E nought values

E nought of the right - E nought of the left

16

When would you use a platinum electrode

When both the oxidised and reduced forms of the metal are in aqueous solution

17

Why is platinum chosen

Inert is does not take part in the electrochemistry
Good conductor to complete the circuit

18

How would you predict if a reaction would occur

Find the species being reduced, calculate its E nought value
Calculate the E nought value of the species being oxidised
Reduction - oxidation
If E nought value > 0 then the reaction will occur

19

What are zinc/carbon cells more commonly known as

Disposable batteries

20

What are the two reactions that take place in zinc/carbon cells

Zn oxidised to Zn2+
NH4+ reduces to NH3 at carbon electrode

21

What are the reactions that occur in a lead/acid battery

Pb + SO42- -> PbSO4 + 2e-
PbO2 + 4H+ + SO42- + 2e- -> PbSO4 + 2H2O

22

How are cells recharged

Reactions are reversible and are reversed by running a higher voltage through the cell than the cell’s E nought

23

Where are lithium ion cells used

Mobile phones
Laptops

24

What is a fuel cell

A cell that is used to generate electric current
Does not require electrical recharging

25

Why is it better to use a fuel cell than to burn H2 in air, even though the same overall reaction occurs

In combustion sulfur contains compounds and nitrogen containing compounds are produced due to the high temperatures
These are bad for the environment
In a fuel cell the only product is water

26

Disadvantages of fuel cells

Hydrogen is a flammable gas with a low bp
Hard and dangerous to transport expensive to buy
Fuel cells have a limited life time
Use toxic chemicals in their manufacture

27

Why might the EMF of a cell change after a period of time

Concentration of ions change

28

How can the EMF of a cell be kept constant

Reagents are supplied constantly so the concentrations of the ions are constant