Study guides › C/P › General Chemistry
Kinetics
Kinetics is about how fast reactions go. You will find rate laws from data tables, use integrated laws and half-lives, apply collision theory and the Arrhenius equation, read energy diagrams, and work out rate laws from mechanisms.
Study this chapter in PrepMed (free)
What this chapter covers
- Reaction Rates & Rate Laws. Method-of-initial-rates tables are a staple of MCAT passages, and the orders come only from the data.
- Integrated Rate Laws & Half-Life. Knowing which plot is linear and how half-life behaves identifies the order of any reaction from time data.
- Collision Theory & the Arrhenius Equation. Why temperature speeds reactions, and how to extract activation energy from an Arrhenius plot, appear often in passages.
- Catalysts & Reaction Energy Diagrams. Energy profiles combine activation energy, ΔH, and the effect of a catalyst in a single diagram.
- Reaction Mechanisms & the Rate-Determining Step. Deriving a rate law from a proposed mechanism, including a fast pre-equilibrium, is a frequent hard question.
Key points to know
- Orders come from experiments, not from coefficients
- Rate change factor = (concentration change factor)^order
- Linear plots: [A] (zero), ln[A] (first), 1/[A] (second)
- First-order half-life = 0.693/k and is constant
- Effective collisions need enough energy and correct orientation
- Higher T: a larger fraction of molecules exceeds Eₐ
- Transition state = peak; intermediates sit in valleys
- Eₐ(reverse) = Eₐ(forward) − ΔH
Try a practice question
For a reaction with rate = k[A]², what happens to the rate when [A] is tripled?
- It triples
- It increases by a factor of 9
- It increases by a factor of 6
- It does not change
Show the answer
B. Second order means rate goes with the square of concentration, so tripling gives 3² = 9 times the rate. Tripling the rate is first-order behavior.
Common questions
What does this chapter cover?
Kinetics covers Reaction Rates & Rate Laws, Integrated Rate Laws & Half-Life, Collision Theory & the Arrhenius Equation, Catalysts & Reaction Energy Diagrams, Reaction Mechanisms & the Rate-Determining Step.
What should I know first?
Orders come from experiments, not from coefficients Rate change factor = (concentration change factor)^order Linear plots: [A] (zero), ln[A] (first), 1/[A] (second)
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.