Question

The correct descending order of the heat liberated (in kJ) during the neutralization of the acids `CH_(3)C O O H (W), HF(X), HCO OH (Y) and HCN`(Z) under indentical conditions `(K_(a) " of" CH_(3) CO OH = 1.8 xx 10^(-5), HCO OH = 1.8 xx 10^(-4), HCN = 4.9 xx 10^(-10) and HF = 3.2 xx 10^(-4))` is
A. `Y gt X gt Z gt W`
B. `X gt Y gt W gt Z`
C. `Z gt X gt Y gt Z`
D. `Z gt W gt X gt Y`

Answer 1

Correct Answer - B
From the `K_(a)` values, strength of the acids is in the order :
`HF gt HCO OH gt CH_(3)CO OH gt HCN`
Weaker the acid, greater is the energy used for ionization and less is the heat liberated or stronger the acid, more the heat is liberated. Hence, order of liberation of heat is
`HF gt HCO OH gt CH_(3) CO OH gt HCN`
or `X gt Y gt W gt Z`