Objectives: Examine voltaic cells with inert electrodes. Calculate the current, in amps, that an electrochemical cell generates as it operates over time.

Review: 2 H+(aq) + 2 Br-(aq)  H2(g) + Br2(aq) Determine if the reaction shown above is spontaneous in the direction written using the table of standard reduction potentials. If it is not spontaneous, how could it be re-written so that it would be spontaneous? What is the maximum voltage that could be produced by the spontaneous version of the reaction?

Voltaic Cells with Inert Electrodes H2 + 2Fe+3  2Fe+2 + 2H+ H2  2H+ + 2e- 2e- + 2Fe+3  2Fe+2 When there are no solid substances in the reaction, the electrodes must be made from other, chemically inert substances. Pt Fe+2 H+ H+ Fe+3 - Graphite, mercury, platinum, gold, etc.

Voltaic Cells with Inert Electrodes H2 + 2Fe+3  2Fe+2 + 2H+ H2  2H+ + 2e- 2e- + 2Fe+3  2Fe+2 Write the shorthand notation for the cell shown to the right. Pt H2 │H+ │ │ Fe+3 │ Fe+2 Fe+2 Fe+3

The Garden Hose Analogy: Volts vs. Amps: The Garden Hose Analogy: Volts can be thought of as the pressure of the water (water flows from high P to low P, like electrons flow from high PE to low PE) Amps (amperes) can be thought of as the amount of water that passes a point in the hose in a given time

Volts vs. Amps: Amps, or amperes, measure the amount of charge that passes a point on the wire per second. AKA – “current” q I = t

Hydrogen fuel cells use the following reaction to power electric cars Hydrogen fuel cells use the following reaction to power electric cars. 2.00 grams of H2(g) is consumed as the cell operates for 600 seconds. 2H2 + O2  2H2O

What is the maximum voltage, Eocell, that can be produced by the cell? 2H2 + O2  2H2O

How many moles of electrons pass through the cell? Individual electrons? 2H2 + O2  2H2O

Calculate the current, in amperes, that passes through the cell. 2H2 + O2  2H2O