MHT CET · Chemistry · Thermodynamics (C)

Calculate the work done during combustion of 0.138 kg of ethanol, \(\left( C _2 H _5 OH ( l )\right)\) at at 300 K . Given: \(R=8.314 Jk ^{-1} mol^{-1}\) and molar mass of ethanol \(=46 g~ mol ^{-1}\).

A \(-7482\text{ J}\)
B \(7482\text{ J}\)
C \(-2494\text{ J}\)
D \(2494\text{ J}\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(7482\text{ J}\)

Step-by-step Solution

Detailed explanation

Stoichiometry coefficients are

Weight of ethanol

0.138 kg = 138 gm,

moles of ethanol

138 / 46 = 3 mole

3 C_{2} H_{5} OH (l) + 9 O_{2} (g) \to 6 {CO}_{2} (g) + 9 H_{2} O (l)

Δ n_{g} = 6 - 9 = - 3

Work = - Δ n_{g} R T

= - (- 3) \times 8.314 \times 300

= 7482 J

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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