A first-order reaction is 20% complete in 12 minutes. What is the rate constant?
k = (2.303/12) log(1/0.8) ≈ 0.0186 min⁻¹.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
Order and Molecularity and Units of Rate Constant
Questions and explanations on reaction order, molecularity, and how to calculate the units of the rate constant, helping clarify key concepts in chemical kinetics.
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A second-order reaction has a rate constant of 0.5 L mol⁻¹ min⁻¹. If the initial concentration is 0.2 mol L⁻¹, what is t
t½ = 1/(0.5×0.2) = 10 min.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A first-order gaseous reaction has an initial pressure of 1.2 atm. After 50 s, the total pressure is 1.6 atm. What is th
x = 0.4, pA = 0.8. k ≈ 0.0081 s⁻¹.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A reaction’s rate increases by 27 times when the concentration of the reactant is increased by 3 times. What is the orde
3ⁿ = 27 → n = 3.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A reaction has a rate constant with units mol⁻¹ L s⁻¹. What is the order of the reaction?
Unit matches second-order.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A first-order reaction has a rate constant of 0.0462 min⁻¹. What percentage of the reactant remains after 15 minutes?
log([R]₀/[R]) ≈ 0.301 → % remaining = 50%.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A zero-order reaction reduces the concentration from 0.18 mol L⁻¹ to 0.09 mol L⁻¹ in 45 s. What is the rate constant?
k = 0.09/45 = 2.0 × 10⁻³ mol L⁻¹ s⁻¹.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A first-order reaction has a half-life of 18 minutes. What percentage of the reactant remains after 54 minutes?
3 half-lives → % remaining = 12.5%.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A first-order reaction has a rate constant of 0.0462 min⁻¹. What is the time required for 75% completion?
t = (2.303/0.0462) log 4 ≈ 30 min.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A first-order reaction has an initial concentration of 0.5 mol L⁻¹ and a rate constant of 0.0693 min⁻¹. What is the conc
[R] = 0.5 / 4 = 0.125 mol L⁻¹.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
For the reaction 3A → 2B, the rate of formation of B is 0.02 mol L⁻¹ s⁻¹. What is the rate of disappearance of A?
−Δ[A]/Δt = 3 × (0.02/2) = 0.03 mol L⁻¹ s⁻¹.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant
A zero-order reaction has a rate constant of 2.0 × 10⁻³ mol L⁻¹ min⁻¹. If the initial concentration is 0.1 mol L⁻¹, how
t = (0.1 − 0.06)/(2.0×10⁻³) = 20 min.
Ref: NCERT Class 12 Chemistry > Chapter 3: Chemical Kinetics > Topic: Order and Molecularity and Units of Rate Constant