It depends entirely on the particular reaction. See the Related Questions link for more about reaction rates.
An inhibitor decreases the reaction rate
A catalyst is a material that speeds up a chemical reaction by providing an alternative pathway with lower activation energy. Alternatively, an inhibitor is a material that slows down a chemical reaction by blocking the active sites on the reactant molecules, preventing them from coming together or reacting.
Inhibitor
Inhibitor~a material used to decrease the rate of reaction
A catalyst speeds up a chemical reaction by lowering the activation energy required for the reaction to occur. It does so by providing an alternative reaction pathway that requires less energy to initiate the reaction. The catalyst itself remains unchanged at the end of the reaction and can be used over and over again.
retardant
In organic chemistry, an activator is a molecule that increases the rate of a chemical reaction, while a deactivator is a molecule that decreases the rate of a chemical reaction.
The rate of the chemical reaction will decrease because oxygen is one of the reactants required for the reaction to occur. With less oxygen available, the reaction will proceed at a slower pace.
negative catalyst.
A material that increases the rate of a reaction is called a catalyst. Catalysts work by lowering the activation energy required for a chemical reaction to occur, thereby increasing the reaction rate without being consumed in the reaction itself.
The concentration of the reactants decreases.
It will increase the rate of the reaction because more particles will be exposed and they will be able to react.This decreases the time to react.