How Temperature and PH levels affects the rate of reactions

Enzymes rely on temperature as the heat helps speed the reactivity, but for Enxymes to work efficiently they need to be at a stable temperature,
otherwise, if you keep increasing the heat it may break apart the bonds that hold the Enzyme together thus making the Enzyme change its active site which is where the Enzymes do their reactants if the shape change is too drastic then the Enzyme might not even help Catalyze by the Enzyme being unable to bind to the Substate.

The name of an Enzyme that has been hit with too much heat is called a Denatured Enzyme, if this does happen it is permanent and cannot be undone, Enzymes also have an optimal temperature and will work with high efficiency at a certain temperature, this is why our bodies always are 37.5 celsius.

Another deciding factor for Enzymes to be more efficient in catalysing is the PH level, which is a measurement of acidity in a substance, if the PH level is too high the rate the Enzyme can work decreases, and if the PH level too low, the Enzyme will also to be able to work at maximum efficiency. 
These changes in PH affect the Enzyme, since too low or high PH levels, change the active site of the Enzyme, sometimes it will still work but since the active site has been changed, how well the Enzyme can fit into the substrate will be worse.

Our bodies work best around 7 PH, but our stomachs work best around 2 PH since the insides of our stomachs are extremely acidic.