Key Terms
Average rate
Calculated over a time interval; use delta[concentration] / delta-t Instantaneous rate: the rate at one specific moment
Example
For N2 + 3H2 --> 2NH3 The rate of H2 consumption is 3 times the rate of N2 consumption.
WHY
Higher temperature means more molecules have enough energy to react.
Exception
Zero-order reactions (covered in Section 4).
Zero order
Rate is independent of concentration First order: rate doubles when concentration doubles Second order: rate quadruples
Example logic
If doubling [A] doubles the rate, m = 1. If doubling [A] quadruples the rate, m = 2.
First order
Half-life is constant; does NOT depend on concentration. t1/2 = 0.693/k Zero order: half-life DECREASES as initial conce
High Ea
Only a small fraction of molecules have enough energy; slow reaction. Low Ea: most molecules have enough energy; fast re
Linear form for graphing
Ln k = (-Ea/R)(1/T) + ln A
Elementary reaction
A single-step reaction that occurs exactly as written; rate law can be written directly from the equation. Reaction mech
When the rate-determining step is the first step
The overall rate law matches the rate law for that step.
Steps
Adsorption --> activation --> reaction --> desorption
Homogeneous catalyst
Same phase as reactants. Reacts with a reactant to form an intermediate; the catalyst is regenerated later in the mechan
Heterogeneous catalyst
Different phase from reactants (usually a solid with gas or liquid reactants). Reaction occurs on the catalyst surface.
Lock-and-key model
Active site and substrate shapes are fixed and complementary. Induced-fit model: active site is flexible and adjusts sha