How does a catalyst work?

How does a catalysts affects the equilibrium constant?

How does a catalyst influence the equilibrium constant ?

How does a catalyst enhance the rate of a chemical reaction? At a constant temperature, does the enthalpy of chemical reaction remain same or change in presence of a catalyst?

How does a catalyst influence the equilibrium constant of a reversible reaction?

How does a solid catalyst enhance the rate of combination of gaseous molecules?

How does a solid catalyst enhance the rate of combination of gaseous molecules?