Rate law

[Shaniya Kerns 4D]

What are the differences between zero-order, first-order, and second-order? How can you tell?

[raina_bandekar_1G]

Zero-order reaction:

The rate of reaction is independent of the concentration of the reactant.
The rate constant has units of concentration/time.
You can tell if a reaction is zero-order by plotting concentration versus time. If the concentration decreases linearly over time, it's likely zero-order.
First-order reaction:

The rate of reaction is directly proportional to the concentration of the reactant.
The rate constant has units of 1/time.
You can tell if a reaction is first-order by plotting the natural logarithm of concentration versus time. If it forms a straight line, it's likely first-order.
Second-order reaction:

The rate of reaction is proportional to the square of the concentration of a single reactant or the product of the concentrations of two reactants.
The rate constant has units of concentration^-1*time^-1.
You can tell if a reaction is second-order by plotting the reciprocal of concentration versus time. If it forms a straight line, it's likely second-order.

[duketh10]

In a zero-order reaction, the rate of the reaction is independent of the concentration of the reactant.
In a first-order reaction, the rate of the reaction is directly proportional to the concentration of one reaction.
In a second-order reaction, the rate of the reaction is proportional to the square of the concentration of one reactant or to the product of concentrations of two reactants.
When looking at graphs:
Zero-order reaction: The plot of concentration vs time is a straight line with a negative slope.
First-order reaction: The plot of the natural logarithm of concentration vs. time is a straight line with a negative slope.
Second-order reaction: The plot of the reciprocal of concentration vs. time is a straight line with a positive slope.