electrolysis and rate of reaction

Electrolysis

A process using electricity to split up compounds into their elements.

Purpose of Electrolysis

To separate out the elements in ionic compounds. Used to extract reactive metals from their oxides.

Electrolysis Equipment

Includes a beaker, an electrolyte, electrodes (anode and cathode), connecting wire, and a power supply (like a battery).

Electrolyte

A liquid or solution containing an ionic compound where the ions are free to move.

Molten Electrolyte

An insoluble ionic compound (like lead bromide or metal oxides) that has been melted so its ions can move.

Aqueous Electrolyte

A soluble ionic compound (like copper sulfate or sodium chloride) that has been dissolved in water. Contains compound ions PLUS H⁺ and OH⁻ from water.

Electrodes (Anode vs Cathode)

Solid conductors (metal or carbon). Anode is positive (right side in diagrams), Cathode is negative (left side).

Electrolysis of Molten Compounds

Negative ions (anions) attracted to positive anode and discharged. Positive ions (cations) attracted to negative cathode and discharged.

Electrolysis for Metal Extraction

Used for reactive metals (more reactive than carbon). Involves electrolysing the molten metal oxide. Example: Aluminium from aluminium oxide.

Electrolysis of Aqueous Solutions - Challenge

Need to figure out which ions go to which electrode because there are ions from the ionic compound AND from the water (H⁺ and OH⁻).

Aqueous Electrolysis - Cathode Rule (Positive Ions)

Negative cathode attracts positive ions (metal ion and H⁺). The ion of the least reactive element will be discharged.

Aqueous Electrolysis - Anode Rule (Negative Ions)

Positive anode attracts negative ions (compound anion and OH⁻). If a halide (F⁻, Cl⁻, Br⁻, I⁻) is present, it's discharged. If not, OH⁻ is discharged.

Oxidation (in Electrolysis)

Loss of electrons. Occurs at the anode.

Reduction (in Electrolysis)

Gain of electrons. Occurs at the cathode.

OIL RIG

Mnemonic: Oxidation Is Loss, Reduction Is Gain (of electrons).

Reversible Reaction

A reaction where the products can react to reform the original reactants.

Double Arrow (⇌)

Indicates a reversible reaction, showing that it can proceed in both forward and backward directions.

Forward vs Backward Reaction

Forward: Reactants → Products. Backward/Reverse: Products → Reactants.

Equilibrium (in Reversible Reactions)

The point when the forward and backward reaction rates are exactly the same.

State of Equilibrium

Concentrations of reactants and products are constant (they don't change), although they are not necessarily equal. Both reactions are still happening.

Closed System (for Equilibrium)

A sealed environment from which no reactants or products can escape. Necessary for equilibrium to be reached.

Position of Equilibrium

Refers to how many reactant particles compared to product particles there are at equilibrium. Lies to the left if more reactants, to the right if more products.

Energy Transfers (in Reactions)

Any chemical reaction involves energy transfers as energy is needed to break chemical bonds and energy is released when chemical bonds form.

Bond Breaking Energy

Energy is needed to break chemical bonds. This is an endothermic process.

Bond Forming Energy

Energy is released when chemical bonds form. This is an exothermic process.

Exothermic Reaction

Net energy released. More energy released making bonds than needed breaking bonds. Products have lower potential energy than reactants. Temperature increases.

Exothermic Energy Profile

Shows products at a lower potential energy level than reactants. Includes a "bump" for activation energy.

Endothermic Reaction

Net energy input. More energy needed breaking bonds than released making bonds. Products have higher potential energy than reactants. Temperature decreases (gets colder).

Endothermic Energy Profile

Shows products at a higher potential energy level than reactants. Includes a "bump" for activation energy.

Activation Energy

The energy needed to get a chemical reaction started. Shown as a bump on energy profile diagrams.

Energy in Reversible Reactions

If the forward reaction is exothermic, the backward reaction is endothermic, and vice versa. The same amount of energy is transferred in each case.

Le Chatelier's Principle

If conditions of a reversible reaction at equilibrium are changed, the equilibrium position will shift to counteract that change.

Le Chatelier's Principle - Temperature

Decrease T: Equilibrium shifts in exothermic direction (releases heat). Increase T: Equilibrium shifts in endothermic direction (absorbs heat).

Le Chatelier's Principle - Pressure (Gases)

Increase P: Equilibrium shifts to side with least molecules (reduces pressure). Decrease P: Equilibrium shifts to side with most molecules (increases pressure).

Le Chatelier's Principle - Concentration

Increase reactant concentration: Equilibrium shifts to the product side (uses up reactant). Decrease reactant concentration (or increase product): Equilibrium shifts to the reactant side.