Which changes have have followed?

Send more info.

Dr. Al-Rawajfeh.

Thanks for you're response.

During the reaction, the nitrate is reduced to ammonia and nitrite.

Hi, You can use least square methods. Such a task is usually done using a programing environment that has optimizing modules (such as Matlab or Aspen Custom Modeler). Please refer to my papers about hydrocracking.

Dr. Sepehr Sadighi

Your question does not make much sense. By definition, a kinetic curve (kinetics) is a function of concentration versus time. The rate dc/dt is a derivative (slope) of this curve at each moment of time. A plotting of [c] versus time is the way to visualize  your data, which is not obligatory. You may treat your kinetic data using tables, but plotting is always helpful. 

@ Dr. Geletii

Thanks for your response.

I want to know that the reaction which is happening, is classified as a "Zero-order", "First-order", or a "Second-order" reaction.

Just by plotting the Concentration vs. Time figure, I could not make a good conclusion about it. Thats why im looking for another method in order to see what kind of reaction it is.

This is a simple problem of chemical kinetics, just read whichever textbook or Google. I could help you but I need raw data. 

@ Dr. Geletii

I appreciate your help. I will send you a personal message.