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AP Chemistry — Thermodynamics and Kinetics

Gibbs energy, reaction rates, and mechanisms

T
thermo_kinetics 22 terms Mar 3, 2026
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Terms 22

1
Enthalpy (ΔH)
Heat of reaction at constant pressure; negative = exothermic; positive = endothermic
2
Entropy (ΔS)
Measure of disorder; positive when products more disordered than reactants
3
Gibbs Free Energy (ΔG)
ΔG = ΔH − TΔS; negative means spontaneous at constant T and P
4
Spontaneity Matrix
ΔH−/ΔS+: always spontaneous; ΔH+/ΔS−: never; mixed signs: temperature-dependent
5
Standard Free Energy and Keq
ΔG° = −RT ln(Keq); Keq = e^(−ΔG°/RT)
6
Reaction Quotient (Q)
Q < Keq: reaction proceeds forward; Q > Keq: reverse; Q = Keq: equilibrium
7
Rate Law
rate = k[A]^m[B]^n; m and n are reaction orders; determined experimentally, not from coefficients
8
Zero-Order Reaction
Rate independent of concentration; [A] = [A]₀ − kt; linear graph of [A] vs t
9
First-Order Reaction
Rate ∝ [A]; ln[A] = ln[A]₀ − kt; linear graph of ln[A] vs t; radioactive decay
10
Second-Order Reaction
Rate ∝ [A]²; 1/[A] = 1/[A]₀ + kt; linear graph of 1/[A] vs t
11
Half-Life (t₁/₂)
First-order: t₁/₂ = 0.693/k; concentration-independent; second-order: t₁/₂ = 1/(k[A]₀)
12
Arrhenius Equation
k = Ae^(−Ea/RT); rate constant depends exponentially on activation energy and temperature
13
Activation Energy (Ea)
Minimum energy for reactants to convert to products; ln(k₂/k₁) = Ea/R(1/T₁−1/T₂)
14
Collision Theory
Reaction requires collision with sufficient energy and correct orientation; rate ∝ collision frequency × fraction with Ea
15
Transition State Theory
Activated complex at energy maximum; ΔG‡ determines reaction rate; TST gives pre-exponential factor
16
Reaction Mechanism
Step-by-step sequence of elementary reactions; each step has its own rate law
17
Rate-Determining Step
Slowest elementary step; determines overall reaction rate and rate law
18
Intermediates vs Transition States
Intermediates: local energy minima, detectable; transition states: energy maxima, fleeting
19
Catalyst
Lowers activation energy; increases rate without being consumed; appears in mechanism
20
Homogeneous Catalyst
Same phase as reactants; e.g. H⁺ in aqueous solution esterification
21
Heterogeneous Catalyst
Different phase; e.g. Pt surface for H₂+O₂; works by adsorption of reactants
22
Enzyme Kinetics
Biological catalyst; saturation kinetics (Michaelis-Menten); highly specific; temperature and pH sensitive