A Level AQA Chemistry - Electrode Potentials and Cells

What are electrochemical cells made from?

Two different metals dipped in salt solutions of their own ions and connected by a wire

What direction do electrons flow in an electrochemical cells?

From the most reactive metal to the least

What is the voltage called between 2 half cells?

Cell potential or EMF

What is an electrode potential?

How easily a metal is oxidised is measured using electrode potentials, and the more negative the more easily it is oxidised

Where does the more negative electrode go when drawing electrochemical cells?

Goes on the left

How do you calculate the cell potential?

E(cell) = E(right) - E(left)

What units are used for electrode potentials?

eV

What metal can you use for electrodes with solutions of the same aqueous ion and why?

Platinum because it's inert and conducts electricity

How do you separate ions in the same phase in conventional diagrams?

With a comma

How do you separate ions in different phases in conventional diagrams?

Using a vertical line

What affects equilibrium?

Temperature, pressure and concentration

Why are standard conditions important?

Ensure the electrode potential value doesn't change so you can compare values for different cells

What occurs in a standard hydrogen electrode?

Hydrogen gas is bubbled through a solution of aqueous H+ ions, and a platinum electrode is used as a platform for the oxidation/reduction reactions

What are the standard conditions?

1.00 moldm-3 concentration, 298K temperature, 100kPa pressure

What is the standard electrode potential of a half cell?

The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

What is the rule regarding standard hydrogen electrodes in conventional diagrams?

ALWAYS shown on the left

What does the electrode potential show you?

How likely something is to gain or lose electrons

Why are electrochemical cells used?

Electrode potentials cannot be measured directly

How do you calculate cell potentials?

E(cell) = E(reduced) - E(oxidised)

What is the standard electrode potential of hydrogen?

0.00 eV

Do very reactive metals have more negative or positive electrode potentials?

More negative

Do very reactive non-metals have more negative or positive electrode potentials?

More positive

How do you know whether a reaction is feasible?

The EMF will be positive

What kind of reactions do non-rechargeable cells use?

Irreversible

What are some examples of non-rechargeable cells?

Remote, torch and smoke alarms

How do non-rechargeable cells use power?

Use small amounts power in short periods of time

Why do batteries leak or explode when you try to reverse the reaction?

The zinc electrode that forms coating because thinner as zinc is oxidised

What kind of reaction does a rechargeable cell use?

Reversible reactions

What are some examples of rechargeable cells?

Mobile phones, laptops, cars

How is the reaction reversed in a rechargeable cell?

Current is supplied to force electrons to flow in the opposite direction around the circuit and reverse the reaction

How do fuel cells work?

Chemicals are stored separately outside the cell, and are fed in when electricity is required

What are some advantages of fuel cells?

1) More efficient

2) No toxic chemical waste/CO2 as only waste product is water

3) No need to recharge like batteries

What are some disadvantages of fuel cells?

1) Hydrogen obtained from electrolysis of water so isn't entirely carbon neutral

2) Hydrogen is also highly flammable

3) Refuelling stations for cars are very rare at the moment