# Pharma Engineering

For Engineer By Engineer

• ## Monday 11 December 2023

Good evening everyone, Today lets see about the order of reaction and the approach to identify it.

Significance of reaction order:
The order of a reaction describes how the rate of a chemical reaction depends on the concentration of the reactants. It's determined experimentally and can be zero, first, second, or even higher order.

Lets see the ways of determining the reaction order.
Usually there will be three ways,
i. Initial rates method,
ii. Integrated rate laws,
iii. Half life method.

Lets see one by one now,

i. Initial Rates Method:

1. Zero Order Reaction:

2. If the rate of the reaction is independent of the concentration of one or more reactants, it's zero order. Experimentally, you'd measure the initial rate of reaction at different concentrations. If changing the concentration doesn't change the rate, it's likely zero order.

3. First Order Reaction:

4. In a first-order reaction, doubling the concentration roughly doubles the rate. Measure the initial rate of reaction at various concentrations and see if there's a proportional change in rate with concentration.

1. Second Order Reaction:

2. Here, doubling the concentration roughly quadruples the rate. You can test this by varying the concentrations and observing how changes affect the rate.

ii. Integrated Rate Laws:

1. Zero Order:

2. Plotting concentration versus time gives a straight line with a slope equal to the rate constant.

3. First Order:

4. Plotting the natural log of concentration versus time results in a straight line, again with the slope equal to the rate constant.

1. Second Order:

2. Plotting the reciprocal of concentration versus time gives a straight line with a slope equal to the rate constant times the initial concentration.

iii. Half Life Method:

1. Zero Order:

2. Changing the initial concentration doesn't affect the half-life, as it remains constant.

3. First Order:

4. The half-life is constant regardless of the initial concentration.

5. Second Order:

6. The half-life decreases as the initial concentration decreases.

Lets consider an example for better understanding.

let's consider a hypothetical reaction:

$\text{A}+\text{B}\to \text{Products}$

And let's assume the rate equation is:

$\text{Rate}=�\left[\text{A}{\right]}^{�}\left[\text{B}{\right]}^{�}$

We'll perform experiments to determine the order with respect to A and B using the methods described earlier.

Initial Rates Method:

1. Zero Order:

2. If the reaction is zero order with respect to A, doubling [A] won't change the rate. Conduct experiments at different [A] while keeping [B] constant. If the rate remains constant, A is zero order. Repeat for different [B] to check its order.

3. First Order:

4. If doubling [A] doubles the rate while [B] is constant, it's likely first order with respect to A. Repeat for different [B] to check its order.

5. Second Order:

6. If doubling [A] quadruples the rate while [B] is constant, it might be second order with respect to A. Repeat for different [B] to check its order.

### Integrated Rate Laws:

Prepare experiments to measure concentrations over time and plot the appropriate graphs to observe linearity or non-linearity.

### Method of Half-Life:

Conduct experiments at different initial concentrations and measure the time taken to reach half the concentration of reactants. Check if the half-life remains constant, doubles, or quadruples when concentrations are altered.

By performing these experiments and analyzing the data according to the methods mentioned earlier, you can deduce the order of the reaction with respect to A and B. Remember, the goal is to observe how changes in concentration affect the rate of the reaction to determine the order with accuracy.

That's it....!!

Hope you enjoyed the post, for any queries please reach us at pharmacalc823@gmail.com

QuizWiz A
bout The Author

Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.