Why does chemical weathering occur more quickly in a hot climate

It occurs more quickly because the chemicals work better at a specific/optimum temperature that the hotter climates have. whereas in a colder climate the chemicals could have been killed off before they start the weathering process. 

Sequoia national park  /  inyo national forest, california, u.s. mount whitney is the tallest mountain in california, as well as the highest summit in the contiguous united states and thesierra nevada—with an elevation of 14,505 feet (4,421 m).