What are electrode potentials measured against?
Standard hydrogen electrodes
What is the standard electrode potential of a half cell?(2)
- The voltage measured under standard conditions
- when a half cell is connected to a standard hydrogen electrode
What are standard conditions?(3)
- any solutions must have a concentration of 1 mol dm^-3
- Temperature must be at 298K
- Pressure must be 100 kPa/1atp
Where should the standard hydrogen electrode be shown?
On the left in the diagram
How do you calculate the cell potential of an electric chemical cell?
Take away the more negative cell from the positive cell
Do you reactive metals have a large negative or positive electrode potential and why?(2)
- Large negative
- Because more reactive metals want to lose electrons to form a positive ion
Do reactive nonmetals have a large or small electrode potential and why?(2)
- Large positive,
- because more reactive nonmetals want to gain electrons to form negative ions.
How do you use electric potentials to predict whether reaction will happen?(3)
– Write down the two half equations
– Write out the full equation
– This shows the most feasible direction of the redox reaction and see if it matches the question
Why could predictions using electrode potentials be wrong?(4)
- reaction kinetics are not favourable: rate of reaction maybe so slow that reaction might not appear to happen or reaction has a high activation enthalpy stopping reaction from happening
- Conditions are not standard: Increasing concentration ions causes equilibrium to shift to the left making it harder to lose an electron or increasing copper ion concentration causes equilibrium the chef to write making easier to gain an electron
What is the voltage of the standard hydrogen electrode half cell?
0v
