Question

Assuming enthalpy of combustion of hydrogen at $273K$ is $-286kJ$ and enthalpy of fusion of ice at the same temperature to be $+6.0kJ$, calculate enthalpy change during formation of $100g$ of ice.

• A. $+1622kJ$
• B. $-1622kJ$
• C. $+292kJ$
• D. $-292kJ$

Answer 1

The correct option is B $-1622kJ$

(I) $H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(l\right);{\Delta }_{c}H=-286kJ$

(II) $H_{2}O\left(s\right)\to H_{2}O\left(l\right);{\Delta }_{fus}H=+6kJ$

On subtracting (II) from (I)

$H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(s\right);$

$\Delta H=-286-6=-292kJ$

$\because$ On formation of $18g$ ice, change in enthalpy $=-292kJ$

$\therefore$ On formation of $100g$ ice, change in enthalpy $=-\frac{292\times 100}{18}=-1622kJ$