Comprehensive notes on Reaction Kinetics, Rate of Reaction, Rate Law, Order (Zero, 1st, 2nd, Pseudo), Molecularity, Half-Life, Activation Energy, Collision Theory, and Catalysis.
Definition: The change in concentration of a reactant or product per unit time. Rate = dx/dt. Unit: mol dm-3 s-1.
Instantaneous Rate: Rate at any specific instant (dx/dt).
Average Rate: Rate over a time interval (Δx/Δt).
At the start, Instantaneous Rate > Average Rate.
Rate Law: Expression relating rate to concentration of reactants raised to some power. Rate = k[A]m[B]n. 'k' is Rate Constant.
Order of Reaction: Sum of exponents (m+n).
1. Zero Order: Rate independent of conc. Rate = k[A]0 (e.g., photochemical rxs).
2. First Order: Rate ∝ [A]1.
3. Second Order: Rate ∝ [A]2 or [A][B].
4. Pseudo-First Order: Higher order reaction behaving as 1st order due to excess of one reactant (e.g., Hydrolysis of Ester in water).
Time required to convert 50% of reactants into products. Formula: t1/2 ∝ 1/an-1 (where 'a' is initial conc, 'n' is order).
Number of reacting molecules taking part in the rate-determining step. Theoretical concept, always a whole number (1, 2, 3). Different from Order (experimental, can be fractional/zero).
Activation Energy (Ea): Minimum energy required for effective collision. Lower Ea → Faster Rate.
Collision Theory: Reaction occurs when molecules collide with (a) Sufficient Energy (≥ Ea) and (b) Proper Orientation.
Arrhenius Equation: k = Ae-Ea/RT. Rate increases exponentially with Temperature.
Substance that increases rate by lowering Ea (providing alternate path) without being consumed.
Homogeneous: Reactants & Catalyst in same phase (e.g., NO gas in SO2 oxidation).
Heterogeneous: Different phases (e.g., Ni solid in hydrogenation of oil).
Physical Methods: Spectrometry (light absorption), Electrical Conductivity (ions), Dilatometric (volume), Refractometric (RI).
Chemical Methods: Titration (e.g., Hydrolysis of ester titrated with NaOH).