Chemical Kinetics

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Chemical kinetics is the study of reaction rates and their mechanisms. It tells us HOW FAST a reaction occurs, while thermodynamics only tells us if a reaction is feasible. It helps us understand fact…

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Rate of reaction is the change in concentration of reactants or products per unit time. For reaction R → P: Rate = -Δ[R]/Δt = +Δ[P]/Δt Negative sign for reactants (decreasing concentration), positive …

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Units of rate = concentration/time Common units: • mol L⁻¹ s⁻¹ (for solutions) • atm s⁻¹ (for gaseous reactions when concentration is expressed as partial pressure) • M s⁻¹ (molarity per second)…

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Rate law is the expression relating reaction rate to the concentration of reactants. General form: Rate = k[A]ˣ[B]ʸ Where: • k = rate constant • [A], [B] = concentrations of reactants • x, y = powers …

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Order of reaction is the sum of powers of concentration terms in the rate law. For Rate = k[A]ˣ[B]ʸ: • Order w.r.t. A = x • Order w.r.t. B = y • Overall order = x + y Examples: • 2NO + O₂ → 2NO₂: Rate…

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Molecularity is the number of molecules participating in an elementary reaction. Differences from Order: • Molecularity: always a whole number (1, 2, 3), theoretical concept • Order: can be fractional…

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For zero-order reaction: Rate = k[R]⁰ = k -d[R]/dt = k Integrating: -∫d[R] = ∫k dt -[R] = kt + I At t = 0, [R] = [R]₀, so I = -[R]₀ Therefore: [R] = [R]₀ - kt Rate constant: k = ([R]₀ - [R])/t…

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Half-life (t₁/₂) is time when [R] = [R]₀/2 From [R] = [R]₀ - kt: [R]₀/2 = [R]₀ - kt₁/₂ Solving: t₁/₂ = [R]₀/2k Key points: • Half-life is directly proportional to initial concentration • Half-life is …