Extreme temperatures and pH levels decrease the activity of enzymes because they become denatured. In the body, most enzymes work optimally around a pH of 7.4. Increasing the pH too high would denature a protein because amino acids that are normally protonated at physiological pH (i.e. acidic residues) would become deprotonated. Lack of protonation would cause collapse of the tertiary and quaternary structures, leading to a decrease in enzyme function. 

Extreme temperatures and pH levels decrease the activity of enzymes because they become denatured. In the body, most enzymes work optimally around a pH of 7.4. Decreasing the pH too low would denature a protein because amino acids that are normally deprotonated at physiological pH (i.e. basic residues) would become protonated. Protonation would cause changes in tertiary and quaternary structures, leading to a decrease in enzyme function, thus the concentration of the product in the catalyzed reaction would decrease as well. 

Catalysts do not shift the equilibrium position of a reaction in favor of the products.

Catalysts speed up chemical reactions by lowering the activation energy (E_a) of reactions, but do not affect the equilibrium position since the change in rate from reactants to products speeds up proportionally to the change in rate from products to reactants (the same K_eq will be achieved whether a catalyst is used or not).

A catalyst affects activation energy; an inhibitory catalyst increases activation energy. Catalysts do not affect equilibrium concentrations of products or reactants.

A catalyst is a substance that increases the rate of a reaction without being altered or used up in the reaction. Both the forward and reverse rates of the reaction are accelerated by a catalyst. Slowing the reverse rate, with an increase in forward rate, would result in a shift in equilibrium. Remember that a catalyst will never change the equilibrium constant (K_eq) of a reaction.

Remember that catalysts affect the kinetics of a reaction, but will not affect the equilibrium. As a result,  will remain the same in the presence of a catalyst, though the reaction rate will accelerate.

The addition of a catalyst lowers the activation energy of a reaction. This means that the rate constant will increase, as the activation energy is a term used to calculate this value.

The Arrhenius equation shows that , where is the activation energy.

The order of the reaction, however, does not increase.

A catalyst must be regenerated in its original form for it to be considered as such. A catalyst is never consumed or produced by a reaction. At once, a catalyst cannot change the thermodynamic properties of a reaction, including the energy absorbed or released. Catalysts typically function by lowering the activation energy, not increasing it.

Catalysts affect reaction rate by lowering the energy of the transition state. In doing so, they lower the activation energy for the reaction and allow it to proceed faster. Catalysts do not affect the equilibrium constant, the equilibrium concentration of reactions, or the equilibrium concentration of products.

Chemical equilibrium is a dynamic state. The reaction still progresses, but in such a manner that the forward and reverse reaction rates are equal, creating the illusion of static chemical concentrations. Adding catalyst to the reaction at equilibrium will still impact reaction rate, but will not impact the chemical concentrations. For this to be achieved, the catalyst accelerates both the forward and reverse reactions, causing the increases to cancel out and leave the equilibrium concentrations unaffected.

In this reaction, step 2 is the rate-determining step and BC₂ is the intermediate. The rate-determining step is always the slowest step in the reaction; the rate of the entire reaction depends on the speed of this step. BC₂ is the intermediate because intermediates are not found in the overall reaction; they are produced and then immediately consumed.