Electrochemical Cells

Question 1

What happens when a metal is dipped into a solution of one of its salts

Answer 1

Some of the metal atoms give up electrons and dissolve to form metal ions, leaving electrons behind on the strip. A dynamic equilibrium forms between the metal atoms and the metal ions

Question 2

What happens at equilibrium between a metal and and a solution of its salts?

Answer 2

The negatively charged electrons that remain on the metal strip set up a potential difference between the metal and the solution.

Question 3

How could you create a larger potential difference between a metal and a solution of its salt?

Answer 3

Use a metal with a greater tendency to produce ions. At equilibrium, there are more ions in solution and more electrons left on the metal strip

Question 4

Dynamic equilibrium

Answer 4

A stage where in a reaction the rate of the forwards reaction is equal to the rate of the backwards reaction so there is no net change in the concentration of the the substances involved in the reaction

Question 5

Potential difference

Answer 5

The difference between two electrode potentials in a cell

Question 6

Salt bridge

Answer 6

An electrolyte solution (e.g. saturated potassium chloride or potassium nitrate in agar jelly) that allows the movement of ions between two half-reactions of an electrochemical cell which are in separate electrode compartments. The salt bridge completes the electrical circuit within the cell

Question 7

Electrochemical series

Answer 7

A list of half-reactions and their electrode potentials. The half-reactions are written as reductions. The series can contain half-reactions containing metals and non-metals

Question 8

Electrode potential

Answer 8

The potential of an electrode measured relative the the Standard Hydrogen Electrode (SHE), under standard conditions

Question 9

The Standard Hydrogen Electrode (SHE)

Answer 9

The standard reference electrode (or half-reaction) for measuring the electrode potentials of cells. Electrode potential of 0 V when operating under standard conditions. Cell consists of hydrogen gas at 1 bar, bubbling over a platinum gelectrode, dipped into a solution of 1 mol dm^-3 HCl

Question 10

e.m.f. (electromotive force)

Answer 10

E^θ cell = E^θ RHS - E^θ LHS. For an electrochemical cell or battery the e.m.f. is the output voltage. Strictly it is the measure of cell potential when zero-current flows

Question 11

What are half-reactions?

Answer 11

The equilibrium between a metal and its ions. They are examples of redox reactions

Question 12

Conductor

Answer 12

A substance that will allow heat or electricity to pass through it easily

Question 13

Standard cell (electrode) potential

Answer 13

The difference in potential between a given electrode under standard conditions and the Standard Hydrogen Electrode

Question 14

A more negative potential means

Answer 14

A stronger reducing agent that loses electrons more easily. Half-reactions with more negative potentials correction to oxidation reactions and go readily from from right to left

Question 15

A more positive potential means

Answer 15

A stronger oxidising agent that accepts electrons more easily. Half-reactions with positive potentials correspond to reduction reactions and go readily from left to right

Question 16

Cell reactions are spontaneous if E^θ cell is

Answer 16

Positive. For this to happen, the more negative electrode potential is written on the left

Question 17

What are the 5 steps to predict a reaction direction?

Answer 17

1) draw horizontal lines against the two half-equations you’re interested in
2) mark the more negative one with a minus sign and the more positive one with a plus sign
3) mark the direction of ‘electron flow’ (from - to +)
4) the ‘electron flow’ will produce a reduction reaction in the half-reaction marked with the plus sign, and an oxidation reaction in the half-reaction marked with the minus sign

Question 18

Lithium ion cell

Answer 18

A type of rechargeable cell where lithium ions move from the negative electrode to the positive electrode during discharge and from the positive one to the negative one during charging. Li+ ions are allowed to flow and to enter and exit the solid structure of the electrodes by a process called intercalation

Question 19

In lithium ion cells what is the negative electrode?

Answer 19

Graphite C

Question 20

In lithium ion cells what is the positive electrode?

Answer 20

CoO2

Question 21

Fuel cell

Answer 21

Cell producing electricity by using fuel reacting with an oxidant