CHEMICAL KINETICS
Class 12 • Handwritten-Style Short Cheat Notes
1. RATE OF REACTION
Average rate = change in concentration / change in time
For R → P : Rate = −Δ[R]/Δt = +Δ[P]/Δt
Instantaneous rate = −d[R]/dt = d[P]/dt
Unit: mol L⁻¹ s⁻¹
2. RATE LAW & RATE CONSTANT
Rate = k[A]^m[B]^n
Order of reaction = m + n
k = rate / [A]^m[B]^n
Order is determined experimentally; molecularity is for an elementary step.
3. ZERO-ORDER REACTION
Rate = k
[R]t = [R]0 − kt
k = ([R]0 − [R]t)/t
t½ = [R]0/(2k)
Graph: [R] vs t → straight line; slope = −k
Unit of k: mol L⁻¹ s⁻¹
4. FIRST-ORDER REACTION
Rate = k[R]
ln([R]0/[R]t) = kt
k = (2.303/t) log([R]0/[R]t)
t½ = 0.693/k → independent of initial concentration
Graph: log[R] vs t → straight line; slope = −k/2.303
Unit of k: s⁻¹
5. HALF-LIFE QUICK VIEW
Zero order: t½ ∝ [R]0
First order: t½ = 0.693/k
After n half-lives: amount left = initial amount / 2^n
6. ARRHENIUS EQUATION
k = A e^(−Ea/RT)
log k = log A − Ea/(2.303 RT)
Two-temperature form: log(k2/k1) = Ea/(2.303R) × (T2−T1)/(T1T2)
Ea = activation energy • A = frequency factor • R = gas constant
7. EFFECT OF TEMPERATURE
Higher temperature → larger fraction of molecules has E ≥ Ea → rate constant increases.
Arrhenius plot: log k vs 1/T → straight line; slope = −Ea/(2.303R)
8. CATALYST
A catalyst provides an alternative pathway with lower activation energy.
It increases reaction rate but does not change ΔG° or equilibrium constant.
9. MOLECULARITY
Number of reacting species involved in one elementary step.
Always a whole number; never zero or fractional.
Class 12 • Handwritten-Style Short Cheat Notes
1. RATE OF REACTION
Average rate = change in concentration / change in time
For R → P : Rate = −Δ[R]/Δt = +Δ[P]/Δt
Instantaneous rate = −d[R]/dt = d[P]/dt
Unit: mol L⁻¹ s⁻¹
2. RATE LAW & RATE CONSTANT
Rate = k[A]^m[B]^n
Order of reaction = m + n
k = rate / [A]^m[B]^n
Order is determined experimentally; molecularity is for an elementary step.
3. ZERO-ORDER REACTION
Rate = k
[R]t = [R]0 − kt
k = ([R]0 − [R]t)/t
t½ = [R]0/(2k)
Graph: [R] vs t → straight line; slope = −k
Unit of k: mol L⁻¹ s⁻¹
4. FIRST-ORDER REACTION
Rate = k[R]
ln([R]0/[R]t) = kt
k = (2.303/t) log([R]0/[R]t)
t½ = 0.693/k → independent of initial concentration
Graph: log[R] vs t → straight line; slope = −k/2.303
Unit of k: s⁻¹
5. HALF-LIFE QUICK VIEW
Zero order: t½ ∝ [R]0
First order: t½ = 0.693/k
After n half-lives: amount left = initial amount / 2^n
6. ARRHENIUS EQUATION
k = A e^(−Ea/RT)
log k = log A − Ea/(2.303 RT)
Two-temperature form: log(k2/k1) = Ea/(2.303R) × (T2−T1)/(T1T2)
Ea = activation energy • A = frequency factor • R = gas constant
7. EFFECT OF TEMPERATURE
Higher temperature → larger fraction of molecules has E ≥ Ea → rate constant increases.
Arrhenius plot: log k vs 1/T → straight line; slope = −Ea/(2.303R)
8. CATALYST
A catalyst provides an alternative pathway with lower activation energy.
It increases reaction rate but does not change ΔG° or equilibrium constant.
9. MOLECULARITY
Number of reacting species involved in one elementary step.
Always a whole number; never zero or fractional.
