Electrochemistry
Easy Overview
Batteries, rust, electroplating — all of these are electrochemistry. It's basically about converting chemical energy into electrical energy and vice versa. Think of it as electrons going on a road trip through wires.
Electrochemical cells
A cell has two electrodes dipped in electrolytes. Electrons flow from one to the other through a wire. The anode is where oxidation happens (electrons leave). The cathode is where reduction happens (electrons arrive). The salt bridge keeps everything balanced — like a referee.
Standard electrode potential
Every metal has a built-in tendency to lose or gain electrons. The standard electrode potential (E°) measures how badly a metal wants to get reduced. More positive E° means it really wants those electrons. Less positive (or negative) means it would rather give them away.
Nernst equation
The voltage of a cell depends on concentration. The Nernst equation tells you exactly how much. E = E° - (0.059/n) log Q. When concentrations are equal (Q = 1), you get the standard voltage. When they're different, the voltage changes. Like a battery dying as it runs out of reactants.
Electrolysis
Forcing a non-spontaneous reaction to happen by pumping electricity in. Like pushing a boulder uphill. Used to extract metals, electroplate jewelry, or split water into hydrogen and oxygen. Faraday's laws tell you how much product you get from a given amount of electricity.
Batteries and fuel cells
Primary batteries are one-time use (alkaline). Secondary batteries are rechargeable (lithium-ion, lead-acid). Fuel cells keep running as long as you supply fuel and oxygen. A hydrogen fuel cell basically combines H2 and O2 to make electricity + water — clean, no pollution.
Key Points
- •Anode: oxidation (lose electrons); Cathode: reduction (gain electrons)
- •Cell potential E°cell = E°cathode - E°anode
- •Nernst equation: E = E° - (0.059/n) log Q at 298K
- •Electrolytic cells use electricity to drive non-spontaneous reactions
- •Faraday's first law: mass deposited ∝ charge passed
- •Faraday's second law: same charge deposits masses proportional to equivalent weights
- •Conductivity of solutions depends on ion concentration and mobility
Practice Questions
- Calculate the EMF of a Daniel cell using the Nernst equation.
- Explain the working of a hydrogen-oxygen fuel cell.
- How much copper is deposited when 0.5 A current is passed for 30 minutes through CuSO4 solution?
- Differentiate between electrolytic and galvanic cells.