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Question #44238

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The Question

Consider the formation of liquid carbon tetrachloride from its constituent elements in their standard states at $300\text{ K}$ in a closed, rigid container:

$\ce{C(graphite) + 2Cl2(g) -> CCl4(l)}$

You are provided with the following thermodynamic data at $300\text{ K}$ : $\bullet$ Enthalpy of sublimation of $\ce{C(graphite)} = 715.0\text{ kJ mol}^{-1}$ $\bullet$ Enthalpy of vaporization of $\ce{CCl4(l)} = 30.0\text{ kJ mol}^{-1}$ $\bullet$ Bond dissociation enthalpy of $\ce{Cl-Cl(g)} = 242.0\text{ kJ mol}^{-1}$ $\bullet$ Mean bond enthalpy of $\ce{C-Cl(g)} = 328.0\text{ kJ mol}^{-1}$ $\bullet$ Universal gas constant $R = 8.3\text{ J K}^{-1}\text{ mol}^{-1}$

Calculate the standard change in internal energy ( $\Delta U^\circ$ ) for the formation of $1\text{ mole}$ of $\ce{CCl4(l)}$ at $300\text{ K}$ .

Options

A.
$-138.02\text{ kJ mol}^{-1}$
B.
$-110.51\text{ kJ mol}^{-1}$
C.
$-143.00\text{ kJ mol}^{-1}$
D.
$-853.02\text{ kJ mol}^{-1}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Bond Enthalpy Pitfall|State vs Path Functions|First Law Consistency

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Bond Enthalpy Pitfall' and 'First Law Consistency'.

Students frequently use the formula $\Delta H = \sum BE(\text{reactants}) - \sum BE(\text{products})$ as a universal black box, forgetting that bond energies apply exclusively to gas-phase species.

The hidden trap requires manually accounting for the sublimation of graphite and the condensation (negative vaporization) of carbon tetrachloride.

Furthermore, the question asks for internal energy ( $\Delta U^\circ$ ), forcing the student to correctly identify $\Delta n_g = -2$ .

Distractor B assumes $\ce{CCl4}$ is a gas (ignoring vaporization and using $\Delta n_g = -1$ ), Distractor C forgets the $\Delta n_g RT$ conversion entirely, and Distractor D forgets the sublimation energy of graphite.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Thermodynamics - Class 11 Part 1
Concept	Bond Enthalpy Pitfall
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free