Question

The heat of combustion of ethane gas is $368\, kcal / mol$. Assuming that $60 \%$ of the heat is useful, how many $m ^3$ of ethane measured at STP must be burnt to supply enough heat to convert $50\, kg$ of water at $10^{\circ} C$ to steam at $100^{\circ} C$ ? (Specific heat of water is $1 \,cal / g$, heat of vaporisation of $H _2 O$ is $540\, cal / g$ )

• A. $2.196\, m ^3$
• B. $1.196 \,m ^3$
• C. $4.196 m ^3$
• D. $3.196 \,m ^3$

Answer 1

Answer: (D)

$\Delta H$ needed for change $=\Delta H_{\text {heating }}+\Delta H_{\text {vaporisation }}$ $=50 \times 10^3 \times 1 \times(100-10)^{\circ} C +540 \times 50 \times 10^3$
$=31500 \times 10^3\, cal$
$\Delta H$ actually needed $=\frac{31500 \times 10^3 \times 100}{60}$
(Since only $60 \%$ of heat is used to do so)
Now $368 \times 10^3$ cal heat is given on combustion by $22.4$ litre
$\therefore \frac{31500 \times 10^3 \times 100}{60}$ heat is given by
$=\frac{22.4 \times 31500 \times 10^3 \times 100}{60 \times 368 \times 10^3}$
$=3.196 \times 10^3 \text { litre }=3.196\, m ^3$