Calculate enthalpy for formation of ethylene from the following data (I) $\mathrm{C}_{\text {(graphite)…

Calculate enthalpy for formation of ethylene from the following data (I) $\mathrm{C}_{\text {(graphite) }}+\mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g})$ $\Delta H=393.5 \mathrm{~kJ}$ (II) $\mathrm{H}_2(g)+\frac{1}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{H}_2 \mathrm{O}(l)$; $\Delta U=-256.2 \mathrm{~kJ}$ (III) $\begin{array}{r}\mathrm{C}_2 \mathrm{H}_4(g)+3 \mathrm{O}_2(g) \rightarrow 2 \mathrm{CO}_2(g)+2 \mathrm{H}_2 \mathrm{O}(l) ; \\ \Delta H=-1410.8 \mathrm{~kJ}\end{array}$
  1. $54.1 \mathrm{~kJ}$
  2. $44.8 \mathrm{~kJ}$
  3. $51.4 \mathrm{~kJ}$
  4. $48.4 \mathrm{~kJ}$

Solution

(I) $\mathrm{C}+\mathrm{O}_2 \longrightarrow \mathrm{CO}_2 ; \quad \Delta H=-393.5 \mathrm{~kJ}$ (II) $\mathrm{H}_2+\frac{1}{2} \mathrm{O}_2 \longrightarrow \mathrm{H}_2 \mathrm{O} ; \quad \Delta H=-286.2 \mathrm{~kJ}$ (III) $\mathrm{C}_2 \mathrm{H}_4+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}$; $\Delta H=-1410.8 \mathrm{~kJ}$ Multiply the equations (I) and (II) by 2 (IV) $2 \mathrm{C}+2 \mathrm{O}_2 \longrightarrow 2 \mathrm{CO}_2 ; \Delta H=-787.0 \mathrm{~kJ}$ (V) $2 \mathrm{H}_2+\mathrm{O}_2 \longrightarrow 2 \mathrm{H}_2 \mathrm{O} ; \Delta H=-572.4 \mathrm{~kJ}$ Add the equations (IV) and (V) and then subtract (III). $2 \mathrm{C}+2 \mathrm{H}_2 \longrightarrow \mathrm{C}_2 \mathrm{H}_4 ; \quad \Delta H=51.4 \mathrm{~kJ}$

Asked in: AP EAMCET 2007

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