Consider the following reactions: (i) H_ (a q) ^ + +OH_ (a q) ^ - arrow H_2 O_ (i) , Δ H =-X_1 ~kJ ~mol^ -1 (ii) H_ 2(a q) +(1)/(2) O_ 2(a q) arrow H_2 O_ ( I ) Δ H =-X_2 ~kJ ~mol^ -1 (iii) CO_ 2(~g) +H_ 2(g) arrow CO_

NEET 2007

Exam: NEET
Year: 2007
Subject: Chemistry
Chapter: Thermodynamics (C)

NEET 2007 · Chemistry · Thermodynamics (C)

Consider the following reactions: (i) H_ (a q) ^ + +OH_ (a q) ^ -...

Consider the following reactions: (i)

\mathrm{H}_{(a q)}^{+}+\mathrm{OH}_{(a q)}^{-} \rightarrow \mathrm{H}_2 \mathrm{O}_{(\mathrm{i})}, \Delta \mathrm{H} =-\mathrm{X}_1 \mathrm{~kJ} \mathrm{~mol}^{-1}

(ii)

\mathrm{H}_{2(a q)}+\frac{1}{2} \mathrm{O}_{2(a q)} \rightarrow \mathrm{H}_2 \mathrm{O}_{(

\mathrm{I}

)} \Delta \mathrm{H} =-\mathrm{X}_2 \mathrm{~kJ} \mathrm{~mol}^{-1}

(iii)

\mathrm{CO}_{2(\mathrm{~g})}+\mathrm{H}_{2(g)} \rightarrow \mathrm{CO}_{(g)}+\mathrm{H}_2 \mathrm{O}, \Delta \mathrm{H} =-\mathrm{X}_3 \mathrm{~kJ} \mathrm{~mol}^{-1}

(iv)

\mathrm{C}_2 \mathrm{H}_{2(g)}+\frac{5}{2} \mathrm{O}_{2(g)} \rightarrow 2 \mathrm{CO}_{2(g)}+\mathrm{H}_2 \mathrm{O}_{(i) \text{, }} \Delta \mathrm{H}=+\mathrm{X}_4 \mathrm{~kJ} \mathrm{~mol}^{-1}

Enthalpy of formation of

\mathrm{H}_2 \mathrm{O}_{(l)}

is:

Options

A $+\mathrm{X}_3 \mathrm{~kJ} \mathrm{~mol}^{-1}$
B $-\mathrm{X}_4 \mathrm{~kJ} \mathrm{~mol}^{-1}$
C $+\mathrm{X}_1 \mathrm{~kJ} \mathrm{~mol}^{-1}$
D $-\mathrm{X}_2 \mathrm{~kJ}^{\mathrm{mol}}{ }^{-1}$

Correct answer

D. $-\mathrm{X}_2 \mathrm{~kJ}^{\mathrm{mol}}{ }^{-1}$

Step-by-step solution

The given reaction represents the formation of

\mathrm{H}_2 \mathrm{O}

, and the

\mathrm{X}_2

represents the enthalpy of formation of

\mathrm{H}_2 \mathrm{O}

. The enthalpy of formation is the heat evolved or absorbed when one mole of substance is formed from its constituent atoms. Related Theory A negative enthalpy change represents an exothermic change where energy is released from the reaction, a positive enthalpy change represents an endothermic reaction where energy is taken in from the surroundings.

Practice Thermodynamics (C) on Quantrex Academy →

More from Thermodynamics (C)