Energy in a cell Today, we will learn to figure out how much energy we can get out of a cell You will need: Periodic Table CALCULATORS!

1 M ion solution (concentration) 25 ºC (temperature) 1 atm (pressure) Electrochemistry: Basic Concepts Standard conditions: 1 M ion solution (concentration) 25 ºC (temperature) 1 atm (pressure)

Copper-Hydrogen cell under standard conditions Electrochemistry: Basic Concepts Copper-Hydrogen cell under standard conditions H2 (g) + Cu2+(aq) → 2H+(aq) + Cu(s) (net ionic equation) Cell notation H2 | H+ || Cu2+ | Cu reduction half-cell CATHODE oxidation half-cell ANODE salt bridge and wire

Eºcell = Eºreduction - Eºoxidation Cell Potential Standard Reduction Potentials (Eº): shows how likely a ½ reaction is to reduce (gain electrons) To find a voltaic cell’s standard potential (how many volts it can use): Eºcell = Eºreduction - Eºoxidation HINT: Write down everything. Show all work. When you do it in your head, you get confused.

Examples: Find the cell potential of a copper-zinc cell. Electrochemistry: Basic Concepts Examples: Find the cell potential of a copper-zinc cell. Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq) Step 1: Cell notation: Zn | Zn2+ || Cu2+ | Cu Step 2: ID ox and red ox red Step 3: Find reduction potentials Zn2+|Zn -0.762 V Cu2+ | Cu +0.342 V Step 4: Equation Eºcell = Eºred - Eºox

Examples: Find the cell potential of a copper-zinc cell. Electrochemistry: Basic Concepts Examples: Find the cell potential of a copper-zinc cell. Step 4: Equation Eºcell = Eºred - Eºox = EºCu2+|Cu - EºZn2+|Zn = 0.342 V – (-0.762 V) = +1.104 V The standard reduction potential of the copper-zinc cell is +1.104 V

Try it out! Calculate the cell potential: Additional Assessment Questions Try it out! Calculate the cell potential: 2Ag+(aq) + Co(s) → Co2+(aq) + 2Ag(s) + 1.08V

In a Electrochemical cell… when Eº = (+), it is spontaneous Electrochemistry: Basic Concepts A spontaneous reaction: proceeds naturally. Voltaic cells are always spontaneous. A non-spontaneous reaction: requires an outside influence to proceed. (eg. forcing the electrons in the opposite direction) In a Electrochemical cell… when Eº = (+), it is spontaneous when Eº = (-), it is not spontaneous

Are these spontaneous or not? Electrochemistry: Basic Concepts Are these spontaneous or not? Eºcell = + 1.322 V Eºcell = + 0.214 V Eºcell = - 0.071 V Eºcell = + 0.421 V Eºcell = - 1.125 V spontaneous not spontaneous

Try it out! Calculate the cell potential to determine if each of these redox reactions is spontaneous. Mn2+ + 2Br- → Br2 + Mn Fe2+ + Sn2+ → Fe3+ + Sn Ni2+ + Mg → Mg2+ + Ni Pb2+ + Cu+ → Pb + Cu2+ -2.251 V, nonspontaneous -0.908 V, nonspontaneous +2.115 V, spontaneous -0.279 V, nonspontaneous