Energy Changes, Rates and Reversible Reactions: notes

Energy Changes

• Exothermic: releases heat, so the temperature rises.
• Endothermic: takes in heat, so the temperature falls. Dissolving ammonium nitrate in water is endothermic.
• Energy level diagram: products lie lower than reactants when heat is released.
• Bond energy: breaking bonds takes in energy, and making bonds gives it out.
• Combustion: burning a fuel in oxygen to release heat. Methane plus oxygen gives carbon dioxide and water.

Rate of Reaction

• Collision theory: particles must collide with enough energy to react.
• Concentration: more concentrated acid gives a faster rate.
• Temperature: hotter particles collide more often and with more energy.
• Surface area: powdered marble reacts faster than marble chips.
• Catalyst: speeds up a reaction and is not used up.

Reversible Reactions

• Reversible reaction: products can change back into reactants.
• Equilibrium: forward and backward reactions run at equal rates.

Industrial Processes

• Haber process: nitrogen plus hydrogen gives ammonia, using an iron catalyst at about 450 degrees Celsius and high pressure.
• Contact process: sulfur dioxide plus oxygen gives sulfur trioxide, using vanadium(V) oxide.

Oxidation and Reduction

• Oxidation: gain of oxygen or loss of electrons. Magnesium plus oxygen gives magnesium oxide, so it is oxidised.
• Reduction: loss of oxygen or gain of electrons. Copper oxide plus hydrogen gives copper, so it is reduced.