${H_2}C = C{H_2}(g) + {H_2}(g) \to {H_3}C - C{H_3}(g)$
\(435 \times 1\,\,\, = \,\mathop {435}\limits_{\overline {\underline {2706} } } \)
\(\Delta H = 2706 - 2831 = - 125\,kJ\)
$R = 8.314\, J\,K^{-1}\,mol^{-1} \,\,\,2.303 \times 8.314 \times 298 = 5705$