Chemical Kinetics — Class 12 Chemistry NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Chemical Kinetics" — 7 important questions with detailed answers for CBSE board exam preparation.
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TL;DR: Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Chemical Kinetics" — 7 important questions with detailed answers for CBSE board exam…
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Key Questions Covered:
- Define rate of reaction. What factors affect the rate of chemical reaction?
- Define order of reaction. How is it determined experimentally?
- A reaction has rate law: Rate = k[A]²[B]. Calculate the order of reaction and…
- Write and explain the Arrhenius equation. What is activation energy?
- For a first-order reaction with k = 0.01 s⁻¹, calculate the half-life.
- Explain the concept of a catalyst. How does it affect activation energy and r…
- + 1 more questions in the full chapter
Solutions Summary:
| Question | Status |
|---|---|
| Define rate of reaction. What factors affect the rate of … | ✓ Solved |
| Define order of reaction. How is it determined experiment… | ✓ Solved |
| A reaction has rate law: Rate = k[A]²[B]. Calculate the o… | ✓ Solved |
| Write and explain the Arrhenius equation. What is activat… | ✓ Solved |
| For a first-order reaction with k = 0.01 s⁻¹, calculate t… | ✓ Solved |
| Explain the concept of a catalyst. How does it affect act… | ✓ Solved |
Showing 6 of 7 questions
Q1: Define rate of reaction. What factors affect the rate of chemical reaction?
Rate of Reaction:
The speed at which reactants are consumed or products are formed per unit time.
Mathematical expression:
Rate = Δ[concentration] / Δt (change in concentration per unit time)
Units: mol/(L·s) or mol·L⁻¹·s⁻¹
Can be expressed for reactants or products:
For reaction: aA + bB → cC + dD
Rate = -(1/a) × d[A]/dt = -(1/b) × d[B]/dt = (1/c) × d[C]/dt = (1/d) × d[D]/dt
Factors affecting rate of reaction:
1. Concentration (Pressure for gases):
Increasing concentration increases collisi...
Q2: Define order of reaction. How is it determined experimentally?
Order of Reaction:
The sum of powers of concentration terms in the rate equation.
For reaction: aA + bB → products
Rate = k[A]^m[B]^n
Order of reaction = m + n
where k = rate constant, m and n are experimentally determined powers (not necessarily equal to stoichiometric coefficients a and b)
Types of order:
1. Zero order: Order = 0, Rate = k, independent of concentration
2. First order: Order = 1, Rate = k[A], rate depends linearly on concentration
3. Second order: Order = 2, Rate = k[A][B] or...
Q3: A reaction has rate law: Rate = k[A]²[B]. Calculate the order of reaction and rate constant unit.
Given: Rate = k[A]²[B]
Step 1: Determine order of reaction
Order = sum of powers of concentration terms
Order = 2 (from [A]²) + 1 (from [B]) = 3
Order of reaction = 3 (third order)
Step 2: Determine unit of rate constant k
From rate equation: Rate = k[A]²[B]
k = Rate / ([A]²[B])
Substitute units:
k = [mol·L⁻¹·s⁻¹] / [mol·L⁻¹]² × [mol·L⁻¹]
k = [mol·L⁻¹·s⁻¹] / [mol³·L⁻³]
k = [mol·L⁻¹·s⁻¹] × [L³·mol⁻³]
k = L²·mol⁻²·s⁻¹
or
k = mol⁻²·L²·s⁻¹
Alternatively expressed as: M⁻²·s⁻¹ (where M = mol/L)
G...
Q4: Write and explain the Arrhenius equation. What is activation energy?
Arrhenius Equation:
k = Ae^(-E_a/RT)
or in logarithmic form:
ln(k) = ln(A) - E_a/RT
or relating two rate constants at different temperatures:
ln(k₂/k₁) = (E_a/R) × (T₂ - T₁)/(T₁ × T₂)
where:
k = rate constant
A = pre-exponential factor (frequency factor, units same as k)
E_a = activation energy (J/mol or kcal/mol)
R = universal gas constant = 8.314 J/(mol·K)
T = absolute temperature (K)
e = Euler's number (2.718)
Activation Energy (E_a):
The minimum energy required for reactants to collide e...
Q5: For a first-order reaction with k = 0.01 s⁻¹, calculate the half-life.
Given: First-order reaction, k = 0.01 s⁻¹
For first-order reaction:
Integrated rate law: ln[A] = ln[A]₀ - kt
or: [A] = [A]₀e^(-kt)
Half-life (t₁/₂) definition:
Time required for concentration to reduce to half of initial value.
At t = t₁/₂, [A] = [A]₀/2
Step 1: Substitute into integrated rate law
ln([A]₀/2) = ln[A]₀ - kt₁/₂
ln[A]₀ - ln(2) = ln[A]₀ - kt₁/₂
-ln(2) = -kt₁/₂
ln(2) = kt₁/₂
t₁/₂ = ln(2)/k
Step 2: Calculate numerical value
ln(2) = 0.693
t₁/₂ = 0.693 / 0.01
t₁/₂ = 69.3 s
Key insigh...
Q6: Explain the concept of a catalyst. How does it affect activation energy and reaction mechanism?
Catalyst:
A substance that speeds up a reaction by lowering the activation energy without being consumed in the reaction.
Characteristics of catalysts:
1. Increases reaction rate (forward and reverse)
2. Not consumed overall (regenerated)
3. Does not change equilibrium position
4. Does not change ΔG (Gibbs free energy)
5. Works by providing alternative reaction mechanism with lower E_a
6. Small amount can catalyze large amount of reactants
7. Specific to particular reactions
Effect on Activatio...
Showing 6 of 7 questions. Visit the full page for complete solutions.
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