AP Chemistry / Unit 5: Kinetics
5.3 Concentration Changes Over Time
Notes
Use graphs to find the order:
- Zero order: $[A]$ vs $t$ is linear.
- First order: $\ln[A]$ vs $t$ is linear; half-life $\displaystyle t_{1/2}=\frac{0.693}{k}$ is constant.
- Second order: $\displaystyle \frac{1}{[A]}$ vs $t$ is linear.
Practice
$\ln[A]$ vs time is a straight line. The reaction is:
Integrated first-order law.
A first-order reaction has $t_{1/2}=10$ min. After 30 min, the fraction left:
Three half-lives.
For a first-order reaction, the half-life:
Constant.
Ready for more? Take the Unit 5 test.