For the gaseous reaction `K + F rarr K^(+) +F^(-), Deltah` was calculated to be `18.4` kcal/mol under conditions where the cations and anions were preverted from combining with each other. The ionisation enthalpy of `K` is 4.3 eV/atom. What is the electron gain enthalpy of F (in eV)? If your answer is `x` report it as `-2x`.

Explanation

`{:(K(g)+F(g)rarrF^(-)(g)+K^(+)(g),,DeltaH =18.4 kCal =0.8 eV),(K(g)rarrK^(+)(g)+e^(-),,IE = 4.3 eV),(F(g)+e^(-)rarrF^(-)(g),,Delta_(eg)H =IE -DeltaH = 0.8 -4.3 =- 3.5 eV),(x =- 3.5,,),(2x =7,,):}`