Final answer:
When ethene reacts with hydrogen in the presence of Ni catalyst, the reaction follows a specific mechanism and is observed to be second order. Without the catalyst, the reaction may follow a different mechanism and it is not known what the order of the reaction would be without further experimental data.
Step-by-step explanation:
When ethene reacts with hydrogen to give ethane in the presence of Ni, the reaction follows a specific mechanism involving the adsorption of hydrogen and ethene on the surface of the catalyst. The reaction proceeds via the formation and breakage of bonds, eventually leading to the formation of ethane. This mechanism is well-studied and established, and the reaction is observed to be second order.
However, if the catalyst is removed and the reaction allowed to proceed without it, the reaction rate may be significantly slower. In this case, the reaction may follow a different mechanism, which might involve a different set of steps and intermediates. Without the catalyst, the reaction may proceed via a stepwise process involving the adsorption of ethene and the diffusion of atoms on the surface.
The order of the reaction without the catalyst cannot be definitively determined without further experimental data. It may be a different order from the second order observed in the presence of the Ni catalyst. To determine the order of the reaction without the catalyst, kinetic experiments would need to be conducted to measure the rate of the reaction under different concentrations of ethene and hydrogen.