ChemistryCBSE Class 12 · Board exam 2023, set 56/5/1 · 2 marks · Very short answer

CBSE Class 12 Chemistry 2023: question 19(a)

Set in the CBSE Class 12 board exam of 2023, paper 56/5/1, section B, question 19(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19(a) · 2 marks · Very short answerElectrochemistry

(i) What should be the signs (positive/negative) for $E_{C e l l}^{\circ}$ and $Δ G^{\circ}$ for a spontaneous redox reaction occurring under standard conditions ?
(ii) State Faraday’s first law of electrolysis.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 56/5/1.

Hints

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

Hint 1

Recall the equation that links $Δ G^{\circ}$ with $E_{ce l l}^{\circ}$ .

Hint 2

For a spontaneous change $Δ G$ must be less than zero; check what that means for $E^{\circ}$ given the minus sign.

Hint 3

Faraday's first law links the mass deposited with the quantity of charge passed.

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.

(i) Using $Δ G^{\circ} = - n F E_{ce l l}^{\circ}$ : a reaction is spontaneous only when $Δ G^{\circ}$ is negative. Since $n$ and $F$ are positive, this requires $E_{ce l l}^{\circ}$ to be positive.
1 mark
(ii) Faraday's first law: the mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte, i.e. $w = Z Q = Z I t$ , where $Z$ is the electrochemical equivalent.
1 mark

Answer: (i) $E_{ce l l}^{\circ}$ positive, $Δ G^{\circ}$ negative; (ii) $w \propto Q$ , i.e. $w = Z I t$

Where the marks are

$E_{ce l l}^{\circ}$ positive (½ mark)
$Δ G^{\circ}$ negative (½ mark)
Correct statement of Faraday's first law: mass deposited ∝ charge passed (1 mark)

Revise the chapter

Chapter: Electrochemistry (notes, formulas, where marks are lost and every past question)
Topic: Nernst Equation, Gibbs Energy and Equilibrium Constant

Practise this chapterBoard-style questions from Electrochemistry, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 56/5/1: every question, by section.

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CBSE Class 12 Chemistry 2023: question 19(a)

Hints

Step-by-step solution

Revise the chapter

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