ChemistryCBSE Class 12 · Board exam 2026, set 56/5/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2026: question 24

Set in the CBSE Class 12 board exam of 2026, paper 56/5/1, section C, question 24, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q24 · 3 marks · Short answerChemical Kinetics

The rate of the chemical reaction doubles when the temperature is raised from 298 K to 308 K. Calculate activation energy ( $E_{a}$ ) for this reaction assuming that it does not change with temperature.
(Given : R = 8·314 J mol $^{- 1}$ K $^{- 1}$ , log 2 = 0·30)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 56/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Doubling of rate means $k_{2} / k_{1} = 2$ .

Hint 2

Use $lo g (k_{2} / k_{1}) = \frac{E _{a}}{2.303 R} \cdot \frac{T _{2} - T _{1}}{T _{1} T _{2}}$ and solve for $E_{a}$ .

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

Arrhenius relation: $lo g \frac{k _{2}}{k _{1}} = \frac{E _{a}}{2.303 R} (\frac{1}{T _{1}} - \frac{1}{T _{2}}) = \frac{E _{a}}{2.303 R} (\frac{T _{2} - T _{1}}{T _{1} T _{2}})$ , with $\frac{k _{2}}{k _{1}} = 2$ .
1 mark
$lo g 2 = \frac{E _{a}}{2.303 \times 8.314} (\frac{308 - 298}{298 \times 308})$
$0.30 = \frac{E _{a} \times 10}{19.147 \times 298 \times 308}$
1 mark
$E_{a} = \frac{0.30 \times 19.147 \times 298 \times 308}{10} = 52722 J mol^{- 1} \approx 52.72 kJ mol^{- 1}$
1 mark

Answer: $E_{a} \approx 52.72$ kJ mol⁻¹ (52722 J mol⁻¹)

Where the marks are

Writes the Arrhenius two-temperature equation with $k_{2} / k_{1} = 2$ (1 mark)
Correct substitution (1 mark)
$E_{a} = 52.7$ kJ mol⁻¹ with unit (1 mark; ½ deducted if the unit is missing or wrong)

Revise the chapter

Chapter: Chemical Kinetics (notes, formulas, where marks are lost and every past question)
Topic: Arrhenius Equation and Activation Energy

Practise this chapterBoard-style questions from Chemical Kinetics, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 56/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 12 Chemistry 2026: question 24

Hints

Step-by-step solution

Revise the chapter

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