Given H2(g)+21O2(g)⟶H2O(l); ΔH∘=−285.9 kJ mol−1…(1) H2(g)+21O2(g)⟶H2O(g); ΔH∘=−241.8 kJ mol−1…(2) We have to calculate H2O(l)⟶H2O(g);ΔH∘= ? On substracting eqn. (2) from eqn. (1) we get H2O(l)⟶H2O(g); ΔH∘=−241.8−(−285.9) =44.1 kJ mol−1
Given: (I) $\begin{aligned}
& \mathrm{H}_2(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{H}2 \mathrm{O}(l) ; \
& \Delta \mathrm{H}^{\circ}{ }{298 \mathrm{K}}=-285.9 \mathrm{kJ} \mathrm{mol}^{-1}
\end{aligned}\mathrm{(II)}\begin{aligned}
& \mathrm{H}_2(\mathrm{g})+\frac{1}{2} \mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{H}2 \mathrm{O}(\mathrm{g}); \
& \Delta \mathrm{H}^{\circ}{ }{298 \mathrm{K}}=-241.8 \mathrm{kJ} \mathrm{mol}^{-1}
\end{aligned}$ The molar enthalpy of vapourisation of water will be :
Held on 9 Apr 2013 · Verified 6 Jul 2026.
241.8 kJ mol−1
22.0 kJ mol−1
44.1 kJ mol−1
527.7 kJ mol−1
Sign in to track your attempts and accuracy.
Sign in to keep a private note on this question. Nothing you write is ever public.
The wavelength of photon ' A ' is 400 nm. The frequency of photon ' B ' is $10^{16} \mathrm{~s}^{-1}$. The wave number of photon ' $C^{\prime}$ is $10^{4} \mathrm{~cm}^{-1}$. The correct order of energy of these photons is :
Given below are two statements: Statement I: The Henry's law constant $\mathrm{K}_{\mathrm{H}}$ is constant with respect to variations in solution's concentration over the range for which the solution is ideally dilute. Statement II: $\mathrm{K}_{\mathrm{H}}$ does not differ for the same solute in different solvents. In the light of the above statements, choose the correct answer from the options given below
For the reaction, $\mathrm{N}_{2} \mathrm{O}_{4} \rightleftharpoons 2 \mathrm{NO}_{2}$, graph is plotted as shown below. Identify correct statements. A. Standard free energy change for the reaction is $-5.40 \mathrm{~kJ} \mathrm{~mol}^{-1}$. B. As $\Delta \mathrm{G}^{\ominus}$ in graph is positive, $\mathrm{N}_{2} \mathrm{O}_{4}$ will not dissociate into $\mathrm{NO}_{2}$ at all. C. Reverse reaction will go to completion. D. When 1 mole of $\mathrm{N}_{2} \mathrm{O}_{4}$ changes into equilibrium mixture, value of $\Delta \mathrm{G}^{\ominus}=-0.84 \mathrm{~kJ} \mathrm{~mol}^{-1}$ E. When 2 mole of $\mathrm{NO}_{2}$ changes into equilibrium mixture, $\Delta \mathrm{G}^{\ominus}$ for equilibrium mixture is $-6.24 \mathrm{~kJ} \mathrm{~mol}^{-1}$.  Choose the correct answer from the options given below :
The half-life of ${ }^{65} \mathrm{Zn}$ is 245 days. After $x$ days, $75 \%$ of original activity remained. The value of $x$ in days is $\_\_\_\_$. (Nearest integer) (Given: $\log 3=0.4771$ and $\log 2=0.3010$)
One mole each of He and $A(g)$ are taken in a $10$ L closed flask and heated to $400$ K to establish the following equilibrium. $A(g) \rightleftharpoons B(g)$. $K_c$ for this reaction at $400$ K is $4.0$. The partial pressures (in atm) of He and $B(g)$ are respectively (at equilibrium) (Assume He, $A(g)$ and $B(g)$ behave as ideal gases) (Given: $R = 0.082$ L atm K$^{-1}$ mol$^{-1}$)
Work through every JEE Main Physical Chemistry PYQ, year by year.