Order of reaction

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KimGiang2F
Posts: 31
Joined: Fri Sep 28, 2018 12:19 am

Order of reaction

Postby KimGiang2F » Tue Mar 12, 2019 2:37 pm

The text states that the rate law for a reaction is determined experimentally and cannot be inferred in general from the chemical equation of the reaction. So how can you determine the order of a reaction?

Manya Bali 4E
Posts: 66
Joined: Fri Sep 28, 2018 12:23 am

Re: Order of reaction

Postby Manya Bali 4E » Tue Mar 12, 2019 2:43 pm

Let's say you have a reaction A + B --> C + D
The equation for the rate of the reaction is as follows:
rate = k[A]^n [B]^m
The powers of [A] and [B] (n and m in the equation) are not affected by the coefficients of the chemical equation. If we had experimental data that showed that doubling [A] (the concentration of A) while [B] remained constant resulted in a quadrupling of the initial rate, then we can conclude that A is second order. Because A is second order, n is 2. Notice how n is NOT 1. The order of A is not affected by its coefficient. If we had experimental data that showed that doubling [B] while [A] was constant resulted in no change of the rate, then we can conclude that B is zero order. Because B is zero order, m = 0.

Thus the overall equation is: rate = k[A]^2 [B]^0 or rate = k[A]^2 so the overall reaction order is 2+0 = 2.


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