JEE Main 2022 · 24 Jun · Shift 2 · Chemistry Q64

← JEE Main 2022 · 24 Jun · Shift 2

ChemistrySingle correct+4 / -1Question 64 of 90

At 25°C and 1 atm pressure, the enthalpies of combustion are as given below:
$\begin{array}{|l|c|c|c|}\hline \text{Substance}&\mathrm{H_2}&\text{C (graphite)}&\mathrm{C_2H_6(g)}\\\hline \Delta_cH^\ominus\ (\mathrm{kJ\,mol^{-1}})&-286.0&-394.0&-1560.0\\\hline\end{array}$
The enthalpy of formation of ethane is

+54.0\ \mathrm{kJ\,mol^{-1}}

-68.0\ \mathrm{kJ\,mol^{-1}}

-86.0\ \mathrm{kJ\,mol^{-1}}

+97.0\ \mathrm{kJ\,mol^{-1}}

Answer and worked solution

Official answer: C

Formation reaction. $\mathrm{2C+3H_2\rightarrow C_2H_6}$ .

Hess's law. $\Delta_fH=2(-394)+3(-286)-(-1560)=-788-858+1560=-86.0$ kJ mol $^{-1}$ .

(C)

Topics:Hess's law and enthalpies of reaction

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JEE Main 2022 · 24 Jun · Shift 2, Chemistry question 64