Reaction Kinetics

What is reaction rate?

Change in concentration over time

How is rate expressed for reactants?

Negative (they decrease)

How is rate expressed for products?

Positive (they increase)

Why are coefficients important in rate equations?

They relate changes in reactants and products

What is the general rate law?

Rate = k[A]^m[B]^n

What is k?

Rate constant

What do m and n represent?

Reaction orders

How do you find reaction order?

From experimental data

What is overall order?

Sum of all exponents

Zero-order rate law?

Rate = k

First-order rate law?

Rate = k[A]

Second-order rate law?

Rate = k[A]² or k[A][B]

What happens to rate if [A] doubles in first-order?

Rate doubles

What happens to rate if [A] doubles in second-order?

Rate quadruples

What happens to rate if [A] changes in zero-order?

No effort

What does k depend on?

Temperature

Does k change with concentration?

No

What determines units of k?

Reaction order

What happens when temperature increases?

Rate increases

Why does rate increase with temperature?

More molecules have enough energy to react

What is activation energy (Ea)?

Energy needed to start a reaction

What happens if Ea is high?

Reaction is slow

What happens if Ea is low?

Reaction is fast

What does a peak represent on an energy diagram?

Transition state

What does each peak correspond to?

One step in mechanism

What is the rate-determining step?

Slowest step (highest Ea)

What is a reaction mechanism?

Series of elementary steps

What determines the overall rate law?

Rate-determining step

What is an intermediate?

Formed then consumed

What is a catalyst?

Speeds up reaction without being used up

How does a catalyst work?

Lowers activation energy

How do enzymes affect reactions?

Lower activation energy

Do enzymes change ΔG?

No