Question

Explain why \[\ce{HCl}\] is a gas and \[\ce{HF}\] is a liquid.

Answer 1

Due to greater electronegativity of \[\ce{F}\] over \[\ce{Cl, F}\] forms stronger \[\ce{H}\] – bonds as compared to \[\ce{Cl}\]. As a result, more energy is needed to break the \[\ce{H}\] – bonds in \[\ce{HF}\] than in \[\ce{HCl}\] and hence the b.p. of \[\ce{HF}\] is higher than that of \[\ce{HCl}\]. Consequently, \[\ce{H - F}\] is liquid while \[\ce{HCl}\] is a gas at room temperature.