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### Course: AP®︎/College Chemistry>Unit 5

Lesson 3: Concentration changes over time

# Zero-order reactions

The integrated rate law for the zero-order reaction A → products is [A]_t = -kt + [A]_0. Because this equation has the form y = mx + b, a plot of the concentration of A as a function of time yields a straight line. The rate constant for the reaction can be determined from the slope of the line, which is equal to -k. Created by Jay.

## Want to join the conversation?

• Is there a half-life for zero-order reaction?
• Yes, zero-order reactions have a half-life equation as well. We can derive it the same way we derive the half-life equations for the first and second-order reactions.

The given integrated rate law of a zero-order reaction is: [A]t = -kt +[A]0. At half-life the concentration is half of its original amount, so [A]t = [A]0/2.
[A]0/2 = -kt + [A]0, after the substitution.
-[A]0/2 = -kt, subtract [A]0 from both sides of the equation.
[A]0/2 = kt, divide by -1 on both sides.
[A]0/2k = t, divide by k on both sides.
So half-life, t1/2, for a first-order reaction is the original reactant concentration divided by two times the rate constant: [A]0/2k

Hope that helps.
• If we increase the concentration of ammonia present above the platinum surface then it will have no effect on the rate of reaction but what if we increase the concentration of ammonia present on the platinum surface? Will the rate of reaction be affected?
According to me, I guess that the rate of reaction will be affected and it will increase. Correct me if am wrong. :)
(1 vote)
• Essentially the platinum metal surface is saturated with ammonia molecules when this reaction is happening. We can’t force more ammonia molecules onto the existing surface because it’s at maximum capacity. The one way we can increase the reaction rate though is by increasing the surface area of the platinum since more surface area can accommodate more ammonia molecules than before. We can do this by either having a larger single sheet of platinum or have more finely divided platinum particles.

Hope that helps.