Answer:
If your just looking for the "why" then this is what i do know about it.
Explanation:
Changes in pH cause amino acids' component atoms and molecules to ionize. This can make an enzyme change shape. These shapes determine function, so changing the shape can impair the enzyme's function, preventing it from speeding up chemical reactions.
Higher temperatures disrupt the shape of the active site, which will reduce its activity, or prevent it from working. The enzyme will have been denatured . Enzymes therefore work best at a particular temperature.
Hope this helps.