when nitrogen reacts with oxygen to form nitrogentrioxide gas, the reaction starts out very quickly..?

Question

then slows down after 10 seconds.why?

Answer 1

well, at the beginning of the reaction all that is in the reaction vessel is nitrogen and oxygen gas not any nitrogentrioxide yet. And according to Collision theory the particals of nitrogen and oxygen need to collide with enough energy and at the correct orientation to bind and form a molecule. So at the beginning of the reaction there are more particals of the oxygen and nitrogen, thus more oppertunities for them to collide at the right orientation. And as the reaction goes on there are less and less, so less chances for the correct orientation, untill the system reaches equilibrium.

Answer 2

I'm guessing because the concentrations of nitrogen and oxygen are decreasing. Rates of reactions are related to the concentrations of the reactants by the rate law for the reaction. As the concentrations decrease, the rate of the reaction also decreases.