Effect of Catalyst on the Rate of Reaction

Describe how does the enthalpy of reaction remain unchanged when a catalyst is used in the reaction.

For the reaction 3A `rightarrow` 2B, rate of reaction `+ (d[B])/(dt)` is equal to ______.

For the reaction \[\ce{3A -> 2B}\], rate of reaction `-("d"["A"])/"dt"` is equal to ______.

Match the items of Column I and Column II.

For a certain reaction large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?

Match the items of Column I and Column II.

For a reaction
\[\ce{2H2O2->[I^-][Alkaline medium]2H2O + O2}\]

The Proposed mechanism is given below: 
(1) H₂O₂+I^- → H₂O+IO^-(slow)
(2) H₂O₂+IO^-→H₂O+I^-+O₂(fast)

(i) Write the rate law for the reaction.
(ii) Write the overall order of a reaction.
(iii) Out of steps(1) and (2), which one is the rate-determining step? 

Explain how and why will the rate of reaction for a given reaction be affected when a catalyst is added.