Temperature, higher concentration and larger surface area

When the temperature is increased the particles move quicker and collide more often

If a solution is more concentrated it means there are more particles of reactant moving about between the water molecules

If one of the reactants is a solid then breaking it up into smaller pieces will increase the surface area

The minimum amount of energy needed by the particles to react

Save money and reduce energy

They can be expensive to buy and can be easily poisined by impurities

Heat is given out

One which transfers energy to its surroundings usually in the form of heat, shown by a rise in temperature

Burning fuels, combustion

Some hand warmers use the exothermic oxidation of iron in the air to generate heat

Heat is taken in

One which takes in energy from its surroundings, usually in the form of heat, shown by a fall in temperature

These are much less common, thermal decomposition

Heat must be supplied to make calcium carbonate decompose to make quicklime