Question

On average a person requires 2870 kcal of energy for leading a normal life. The amount of cane-sugar in g must be consumed, if all the required energy has to be derived from the combustion of cane-sugar is:

[Given : The heats of formation for cane-sugar $\left(s\right)$, $C{O}_2\left(s\right)$ and $H_{2}O\left(l\right)$ are -530, -94.0 and -68.3 kcal respectively.]

• A. $545.2$
• B. $727.6$
• C. $421.2$
• D. $213.5$

Answer 1

Answer: (B)

$727.6$

$C_{12}{H}_{22}{O}_{11}+12O_2\to 12{CO}_2+11H_{2}O$

$\Delta H_{com}=$ Heat of combustion

$=(+530.31)+\left(12\right(-94.06)+11(-68.31)$

$=+530.31+(-1128.72+(-751.31\left)\right)$

$=-1880.02+530.31=-1349kcal$ for $1mole$ (energy liberated)

This much energy is obtained and utilized from 1 mole of cane-sugar.

$\therefore$No. of moles needed $=\frac{2870}{1349}=2.127mole$

Molecular mass of $C_{12}{H}_{22}{O}_{11}=342$

Mass of canesugar $=2.127\times 342gm=727.6gm$