Why does heat speed up reactions?
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Atoms are surrounded by a “cloud” of electrons. Electrons all have the same charge and like charges repel, and the closer like charges are, the greater this repelling force. Therefore for the atoms to get close enough together to form a bond they need enough energy to overcome the repulsive force.
Temperature is essentially a measure of the average kinetic energy of the constituent particles. The higher the temperature the greater the average kinetic energy. Since the average is higher, there will be a larger population of atoms with sufficient kinetic energy to overcome the repulsive force, so there are more opportunities for the reaction to occur.
It should be noted that even in an exothermic reaction (a reaction in which energy is liberated) the reactants must still be provided enough energy to overcome the repulsion. This is why gasoline vapor and oxygen doesn’t spontaneously combust when mixed. It requires the flame to provide the initial push of kinetic energy. Once you light the vapors, the exothermic reaction provides all the extra energy needed to keep the reaction going until you run out of fuel or oxygen.
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