Rate of reaction
Particles react only when they collide with at least the activation energy. Rate increases with concentration (or gas pressure) and surface area, because collisions become more frequent; with temperature, because particles collide more often and more collisions have enough energy; and with a catalyst, which provides a route with lower activation energy. Rate is the gradient of a product-against-time graph.
≈ 45 minReversible reactions and equilibrium
A reversible reaction can go both ways (). In a closed system it reaches dynamic equilibrium: forward and backward rates are equal, so concentrations stay constant. Changing conditions shifts the equilibrium to oppose the change: higher pressure favours fewer gas moles; higher temperature favours the endothermic direction. The Haber process () uses about , atm and an iron catalyst as a compromise between yield and rate.
≈ 45 minRedox
Oxidation is gain of oxygen, loss of electrons, or an increase in oxidation number. Reduction is loss of oxygen, gain of electrons, or a decrease in oxidation number. They always happen together: a redox reaction. The oxidising agent is itself reduced; the reducing agent is itself oxidised.
≈ 35 min