Question

$C_{2}H_{6}\left(g\right) +3.5O_{2}\left(g\right)\to2CO_{2}\left(g\right) +3H_{2}O\left(g\right)$
$S_{\text{vap}}\left(H_{2}O,\ell\right)=x_{1}$ cal $K^{-1}$(boiling point $= T_{1}$)
$\Delta H_{f}\left(H_{2}O, \ell\right)=x_{2}$
$\Delta H_{f}\left(CO_{2}\right)= x_{3}$
$\Delta H_{f}\left(C_{2}H_{6}\right)= x_{4}$
Hence, $\Delta H$ for the reaction is

• A. $2x_{3} + 3x_{2} - x_{4}$
• B. $2x_{3} + 3x_{2} -3x_{4} + 3x_{1}T_{1}$
• C. $2x^{+} + 3x_{2} - x_{4} - 3x_{1}T_{1}$
• D. $x_{1}T_{1} + x_{2} + x_{3} - x_{4}$

Answer 1

Answer: (B)

$H_{2}O\left(l\right)\to H_{2}O\left(g\right) \Delta H_{\text{vap}} =\Delta S_{\text{vap}} T_{B.P}=x_{1}T_{1}$
$\Delta H_{f}\left(H_{2}O, g\right)=\Delta H_{f} \left(H_{2}O, l\right)+\Delta H_{\text{vap}} =x_{2} +x_{1}T_{1}$
$\Delta H_{\text{reaction}}=2\Delta H_{f'}\left(CO_{2},g\right)+3\Delta H_{f}\left(H_{2}O, g\right)-\Delta H_{f}\left(C_{2}H_{6,g}\right)$
$=2x_{3} +3 \left(x_{2}+ x_{1}T_{1}\right)- x_{4}=2x_{3} +3x_{2} +3x_{1}T_{1} -x_{4}$