Question

The first ionization energy for $Li$ is $5.4$ eV and electron affinity of $Cl$ is $3.61$ eV. The $\Delta H$ (in kJ/mol) for the reaction $Li\left(g\right)+Cl\left(g\right)\to L{i}^{+}\left(g\right)+C{l}^{-}\left(g\right)$ is:

(If the resulting ions do not combine with each other)

• A. $70$
• B. $100$
• C. $172$
• D. $270$

Answer 1

Answer: (C)

$172$

Given $Li\left(g\right)\to {Li}^{+}$+$e^{-}$ IE=$5.4$eV/atom

$Cl\left(g\right)+e^{-}\to {Cl}^{-}$(g) $E_z=-3.61$eV/atom

Add both reaction:

$\Delta H=(5.4-3.61)$eV/atom

$=((5.4-3.61)\times 1.6\times {10}^{-19}\times 6.023\times {10}^{23}\times {10}^{-3})=172.4kJ{mol}^{-}$