chemical reaction & N2 H2 in gaseous phase. thanks for your help!?

Question

a) a chemical reaction MAY occur when molecules of reactants collide together. explain why it is that at a given temperature, only a certian proportion fo molecules react together on collision.
b) why do N2 and H2 react very slowly in the gaseous phase, but much more rapidly in teh presence of an iron catalyst?

Answer 1

a) Space. Even though you may have 1 mole in a liter of volume - most of that volume is just empty space. You MUST get the molecules to collide to get a reaction, and a high temperatures, this can get complicated because the molecules are moving around faster. So it becomes a probability - what percentage of the molecules will collide with other molecules given their enivronment.

You can increased the probability by applying pressure - or decreasing the volume, to get more of the molecules in a tighter configuration.

b) Usually the reaction with a catalyst occurs on the surface of the catalyst. So the H2 or N2 (or both) is temporarily bound to the catalyst. This increases the probability that is will be hit by another gas molecule - and hence a reaction taking place.

Answer 2

a) At a given temprature, the molecules have only a certain amount of energy. That energy may or may not be suffiecient to make sure the reactant molecules even collide and "stick" with each other to finally react. A more mathematical proof is given in statistical probabilitistic kinetics.

b) In the gaseous state, the molecules are far from each other. Compare with liquid and solid state mixtures. In order to form a product, the reactant MUST be at least next to each other and must overcome the activation energy of reaction. The presence of the catalyst accomplishes this nicely by sort of "immobilizing" the N2 and H2 molecules next to each other on the surface of the catalyst or aligning the molecules just right, thereby lowering the energy reaquired for the reactions.

Answer 3

This reaction has a high activation energy. The presence of a catlyst (such as iron) dramatically lowers it.