Explain why and how theories may be changed or replaced over time.

Theories may be changed over time as new information is discovered or new technologies are developed. New developments lead to changes in experimental methods, which provide information that may or may not support the existing theory. If the theory is still supported, it may be updated. If it is not supported but the results are true and relevant, the theory may be replaced.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.