Ch9/10 - Galvanic Cells & Electrolysis

Explain electrochemistry

• Since REDOX reactions involve transfer of electrons, its possible to physically separate the oxidant (oxidising agent) and reductant (reducing agent) into different locations

• The process of electrons moving from reductant to oxidant is called ELECTRICITY

• Redox reactions can be used to generate electricity if the two-half reactions are PHYSICALLY SEPARATED

Explain a daniell/galvanic/electrochemical cell

• ANY electrochemical cell consists of TWO half cells. Each half cell consists of an electrode (metal or graphite) in contact with an electrolyte solution (sol. containing ions).

• OXIDATION takes place at the ANODE (-ve electrode) as it generates electrons. (An Ox)

  • Oxidation = loss of electron

• REDUCTION takes place at the CATHODE (+ve electrode) (Red Cat)

  • Reduction = gain of electrons

• Electrons flow from the ANODE to CATHODE (-ve to +ve)

Explain ‘E naught’ values in redox reactions

• The voltage produced is a measure of the driving force for a redox reaction to occur.

• This property is used to rank the strength of different oxidising agents.

• The table of standard reduction potentials is such a ranking. These are found on your Data Sheet and are called ‘E naught’ values.

Explain what it means when the E^o_red is positive or negative on the data sheet

• The more positive the value of E^o_red the stronger the oxidising agent (reduction).

• The more negative the value of E^o_red the stronger the reducing agent (oxidation).

How do you get the E^o_ox from reading the data sheet?

If you read the table backwards (right to left), the electrons are now gained and the E^o sign is flipped; E^o_ox

The numerical value of  - E^o_red = E^o_ox

How do you know if a reaction is spontaneous or non-spontaneous?

The E^ocell determines whether a reaction will be spontaneous or not (i.e. whether electricity will be produced). When adding two half cell e naughts together;
a positive E^o = spontaneous
a negative E^o = nonspontaneous

Explain electrolysis

• If a reaction is nonspontaneous, it is possible to supply an external voltage to chemicals and ‘force’ a chemical reaction to occur.

• Forcing chemical reactions to occur by supplying electricity is called Electrolysis