catalyst/enzyme

[aaronharouni]

Why doesn't a catalyst/enzyme change the reaction rate?

[Soumya Ravichandran 4H]

A catalyst/enzyme does change the rate of the reaction by changing the activation energy needed for the reaction to proceed to completion.

[Heesu_Kim_1F]

^I agree. A catalyst/enzyme does change/increases the rate of reaction by lowering the activation energy. However, a catalyst/enzyme does not change the equilibrium constant for a reaction. Also, a catalyst or enzyme (itself) is not changed during a reaction.
Hope this helps!

[Diana Bibireata 1B]

A catalyst lowers the activation energy so it ends up speeding up the rate of the reaction.

[Jocelyne Milke 1G]

A catalyst speeds up the reaction but does not get consumed in the reaction and doesn't change the rate constant.