Electrochemistry Flashcards
What is electrolysis?
The decomposition of a compound into its elements by an electric current.
Which ions appear at the anode?
Negative ions (anions)
Which ion appears at the cathode?
Positive ions (cations)
Principles to use to find the mass of substance deposited at electrode.
- Equation Q = I×t
* Unit of the faraday is Cmol¹(minus)
What is 1 Faraday?
The quantity of electric charge carried by one mole of electrons or singly charged ions. ( e.g Pb² + 2e –> Pb , this shows that two moles of electrons are required per mole of Pb formed , so we multiply 96500 by 2)
Equation for Avogadro constant.
L = charge on one mole of electrons/ charge on one electron.
What is the standard Electrode potential for a half cell?
The voltage measured under standard conditions, with a standard hydrogen electrode as the second half cell.
The more positive the value of E.p is…….
The easier it is to reduce the ions on the left , so the metal on the right is relatively unreactive and it is a relatively poor reducing agent.
The more negative the value of E.p is…….
The more the metal is a reducing agent, it is relatively reactive.
What is made when two half cells are connected together?
An electrochemical cell.
What is the use of the salt bridge?
To complete the electrical circuit allowing the movement of ions between the two half-cells so that ionic balance is maintained. However it doesn’t allow the movement of electrons.
What are the standard conditions when comparing electrode potentials.
- Conc. of ions at mol/dm³
- Temp. of 25⁰C
- Gases at pressure of 1atm.
- The value of the E.p of the half cell is measured relative to the standard hydrogen electrode.
Define standard E.p for a half cell.
The voltage measured under standard conditions with a standard hydrogen electrode as the other half cell.
At which terminals of the cell do reduction and oxidation occur?
Reduction at the positive.
Oxidation at the negative.
Which element is at the positive terminal?
The element that is easier to reduce.
For electrodes of non-metals……..
Electrical contact with the solution is made by using platinum wire or foil (for gases, a gas chamber is used and for liquids it is kept at the bottom of the beaker with its ions above it)
To calculate the standard cell potential (difference between E⁰ values or cell voltage)
Always subtract the less positive E⁰ value from the more positive E⁰ value.
How to determine electron flow.
From negative terminal to positive or from the harder to reduce(-) to the easier to reduce(+).
What word is used if a reaction is likely to occur?
Feasible.
If the forward reaction is feasible then…..
The backward reaction isn’t feasible.
When is the reaction not feasible?
If the difference in their values of E⁰ is less than 0.3. (Under nonstandard conditions. May not occur)
OR
If the sum of the sum of the voltages of the half cells is negative.
OR
If reactants shown are not the strongest oxidising and reducing agents.
What happens in the half cell equation as the values of E⁰ get more negative?
- Species on the left of the equation become weaker oxidising agents.
- Species on the right become stronger reducing agents.
How does value of E⁰ vary with ion Conc.
If Conc. of ion on the left is greater than 1mol/dm then E⁰ becomes more + and if Conc. is less than 1dm/mol then E⁰ becomes more -.( opposite happens for the species on the right)
State Nerst equation.
E = E⁰ + RT/zF x ln ox form/red form.
- where E is electrode potential under nonstandard conditions.
- z is number of electrons transferred.
- F is value of Faraday constant in C/mol.
- E⁰ is standard electrode potential.
