Question

How does reaction rate change with time?

Answer 1

We know that according to collision theory there are only two ways to increase the reaction rate and increase the frequency of collision as well as including increasing fraction of collisions which are too effective.
Also whenever we speed up the particle by increasing their temperature we can observe there is greater change and now that they will pop and collide with each other and the reaction rate goes up by then. Therefore the total energies within particles also increase so whenever they do collide with one another simultaneously they also do so with more in increasing energy here increasing energy is the fraction of the effective collision as per collision theory.

Complete answer:
On first-hand the rate of a reaction decreases as time progresses and the Collision Theory explains that rate of reaction only depends on reactant particles which are colliding with energy in the excess of Activation Energy for reaction. As reaction progress reactants are being tuned into product so the number of the reactant particles from left is in decreasing order.
Thus if the amount of reactant particle is decreased as per reaction the progress by then has a chance of being successful in collision which must also decrease and with ultimate factor whenever all the reactant and particle have the reaction they must stop and by then rate has arrived to zero.
When concentrations of reactant are raised to reaction proceed more quickly. Thus this is due to the increasing number of molecules that we have acquired that require energy. For gas states, the increase in pressure has the same effect as the increasing concentration.
When the solid as well as liquid reacts with increase in surface area of solid will increase the rate of reaction. A decrease in size of particle causes an increase in solids with total surface area.

Note: Note that the raise in a reaction with temperature by $10\text{ }{}^\circ C$ we can double or triple the reaction rate. This all is due to the increasing number of particles that we have minimum energies required. Also the rate of reaction is decreased with decrease in temperature.
As the catalysts have capacity, they can lower activation energy as well as increase reaction rate without being totally consumed in reaction.