When `100mL` of `1.0M HCl` was mixed with `100 mL` of `1.0 M NaOH` in an insulated beaker at constant pressure, a temperature increase of `5.7^(@)C` was measured for the beaker and its contents (Expt.1). Because the enthalpy of neutralisation of a strong acid with a strong base is constant `(-57.0kJmol^(-1))` this experiment couldbe used to measure the calorimeter constant. In a second experiment (Expt.2), `100mL` of `2.0M` acetic acid `K_(a)=2.0xx10^(-5))` was mixed with `100mL` of `1.0M NaOH` (under identical conditions to Expt. 1) where a temperature rise of `5.6^(@)C` was measured.
Enthalpy of dissociation (in `kJ mol^(-1)`) of acetic acid obtained from the Expt. 2 is

Options

A. 1
B. 10
C. 24.5
D. 51.4

Answer

A

Explanation

Heat capacity of calorimeter = `57xx10^(3)xx0.1-(4.2xx200xx5.7)/5.7 = 1000-840 = 160 J//K`
Energy required to dissociate 0.1 moles of `CH_(3)COOH` (100 ml, 2M)
` = (57 xx 10^(3) xx 0.1) - (4.2 xx 200 xx 5.6) - (160 xx 5.6)`
` = (57 xx 10^(3) xx 0.1) - (1000 xx 5.6) = 1000 xx 0.1 = 100J`
`implies` Enthalpy of dissociation =` 100 J//0.1 moles = 1000J/mol es = 1 KJ//mol`