what criteria would you apply to show that a particular substance taking part in a reaction is not a reactant but a catalyst
Answers
Answer:
A Catalyst is a substance which acclerates the rate of a chemical reaction without undergoing any change in its chemical composition or mass during the reaction. A catalyst acclerates the rate of a reaction by lowering the activation energy.
Explanation:
Characteristics of Catalysis :
(i) A Catalyst remains unchanged in mass and chemical compositions at the end of reactions. However its physical state can be change.
(ii) Finely devided state of catalyst is more efficient for the reactions because surface area increases and more adsorption take place.
(iii) A small amount of catalyst is generally sufficient to catalyse almost unlimited reaction but in some cases the rate of reaction depends on amount of catalyst.
(iv) A catalyst cannot initiate reaction. But some times the activation energy is so large that practically
a reaction may not start until a catalyst lowers the activation energy significantly. For example, mixture of hydrogen and oxygen do not react at room temperature but the reaction occurs very rapid in presence of Pt black.
(v)
Catalyst are generally specific in nature. A substance which act as a catalyst in a particular reaction,
fails to catalyse other reaction.
(vi) Catalyst cannot change equilibrium state but it help to attain equilibrium quickly.
(vii) A catalyst does not change the enthalpy, entropy and free energy of a reaction.
(viii) Optimum temperature : There is a particular temperature at which the efficiency of a catalyst a maximum this temperature is known as optimum temperature. On either side the optimum temperature, the activity of catalyst decreases.
A catalyst would appear in the reaction machenism, but not in the overall chemical reaction but if it is a reactant it would appear in the overall chemical equation.
Hope it helps!!