catalyst點樣影響個rate of reactoin? 有咩experimant可以prove到??

There are two kinds of catalyst : positive catalyst and negative catalyst
The postive catalyst can increase the rate of the reaction while the negative catalyst can slow down the reaction rate.
The catalyst provides an alternative pathway of reaction mechanism which involves a lower activation energy .
For example , in the reaction of iodide ions and persulphate ions :
we could carry out two sets of experiment :
1 . Add sodium thiosulphate solution , starch indicator and a solution of iron ( II ) ions / iron ( III ) ions into a solution of iodide ions before adding the solution of persulphate ions into it . Then , add the solution of persulphate ions into the above mixture and measure the time taken for the first appearance of blue colour of the solution .
2 . Repeat the above experiment . However , no iron ( II ) ions nor iron ( III ) ions should be added into the reaction mixture this time .

After the experiment , we could find out that the time taken for the first appearance of blue colour of the solution in the experimental set-up 1 is much shorter than that in the experimental set-up 2 . This experiment can illustrate the effect of the catalyst on the reaction rate .

Just setup a control without catalyst to compare the rate of reaction.