Find the heat change in the reaction : `NH_(3)(g)+HCl(g)rarr NH_(4)Cl(s)` from the following data
`{:(NH_(3)(g)+aq rarr NH_(3)(aq)",",Delta H=-8.4"K. Cal."),(HCl(g)+aq rarr HCl (aq)",",Delta H=-17.3"K. Cal."),(NH_(3)(aq)+HCl(aq)rarrNH_(4)Cl(aq)",",Delta H=-12.5 "K. Cals."),(NH_(4)Cl(s)+aq rarr NH_(4)Cl(aq)",",Delta H=+3.9 "K.Cal."):}`

Options

A. `-42.1`
B. `-34.3`
C. `+34.3`
D. `+42.1`

Answer

A

Explanation

`NH_(3(g))+HCl_((g))rarr NH_(4)Cl_((s)), Delta H = ?`
Desired equation = eq(i) + eq(ii) + eq(iii) - eq(iv)
`Delta H=(-8.4)+(-17.3)+(-12.5)-(3.9)`
`Delta H =-42.1 KCal`