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NEET CHEMISTRYThermodynamicsEasy

Question

For the reaction, 2Cl(g)→Cl2(g)2\text{Cl(g)} \rightarrow \text{Cl}_2\text{(g)}, the correct option is:

A

ΔrH>0\Delta_r H > 0 and ΔrS>0\Delta_r S > 0

B

ΔrH>0\Delta_r H > 0 and ΔrS<0\Delta_r S < 0

C

ΔrH<0\Delta_r H < 0 and ΔrS<0\Delta_r S < 0

D

ΔrH<0\Delta_r H < 0 and ΔrS>0\Delta_r S > 0

Step-by-Step Solution

Let us analyze the given reaction: 2Cl(g)→Cl2(g)2\text{Cl(g)} \rightarrow \text{Cl}_2\text{(g)}

  1. Enthalpy change (ΔrH\Delta_r H): The reaction involves the formation of a Cl-Cl\text{Cl-Cl} bond from two isolated gaseous chlorine atoms. Bond formation is an exothermic process because energy is released when a stable bond is formed. Therefore, the enthalpy change is negative (ΔrH<0\Delta_r H < 0).

  2. Entropy change (ΔrS\Delta_r S): In this reaction, two moles of gaseous atoms combine to form one mole of a gaseous molecule. Since the number of gaseous particles decreases (Δng=1−2=−1\Delta n_g = 1 - 2 = -1), the randomness or disorder of the system decreases. Therefore, the entropy change is also negative (ΔrS<0\Delta_r S < 0).

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Thermodynamics. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYThermodynamicsreactiontextclgrightarrowtextcltextgcorrect

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For the gas phase reaction, $\text{PCl}_5\text{(g)} \rightleftharpoons \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)}$, which of the following conditions is correct?

A.$\Delta H = 0$ and $\Delta S < 0$
B.$\Delta H > 0$ and $\Delta S > 0$
C.$\Delta H < 0$ and $\Delta S < 0$
D.$\Delta H > 0$ and $\Delta S < 0$
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One mole of an ideal gas at $300\text{ K}$ is expanded isothermally from an initial volume of $1\text{ litre}$ to $10\text{ litres}$. The $\Delta E$ for this process is: ($R = 2\text{ cal mol}^{-1}\text{K}^{-1}$)

A.$1381.1\text{ cal}$
B.Zero
C.$163.7\text{ cal}$
D.$9\text{ lit. atm}$
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What is the amount of work done by an ideal gas, if the gas expands isothermally from $10^{-3} \text{ m}^3$ to $10^{-2} \text{ m}^3$ at $300 \text{ K}$ against a constant pressure of $10^5 \text{ N m}^{-2}$?

A.$+270 \text{ kJ}$
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C.$+900 \text{ kJ}$
D.$-900 \text{ kJ}$
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Match List-I (Equations/Conditions) with List-II (Type of processes) and select the correct option. **List-I (Equations)** (a) $K_p > Q$ (b) $T < \frac{\Delta H}{\Delta S}$ (for $\Delta H > 0$) (c) $K_p = Q$ (d) $T > \frac{\Delta H}{\Delta S}$ (for $\Delta H > 0$) **List-II (Type of processes)** (i) Non-spontaneous (ii) Equilibrium (iii) Spontaneous and endothermic (iv) Spontaneous

A.(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
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The enthalpy of neutralization of which of the following acids and bases is nearly –13.6 Kcal [Roorkee 1999]

A.HCN and NaOH
B.HCl and KOH
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The heat of combustion of carbon to $\text{CO}_2$ is $-393.5 \text{ kJ/mol}$. The heat released upon the formation of $35.2 \text{ g}$ of $\text{CO}_2$ from carbon and oxygen gas is:

A.$-315 \text{ kJ}$
B.$+315 \text{ kJ}$
C.$-630 \text{ kJ}$
D.$+630 \text{ kJ}$
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A system is changed from state A to state B by one path and from B to A by another path. If $E_{1}$ and $E_{2}$ are the corresponding changes in internal energy, then [Pb. PMT 2001]:

A.$E_{1} + E_{2} = -ve$
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A.+ 590 joules
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