Question

Heat of a reaction is defined as the amount of heat absorbed or evolved at a given temperature when the reactants have combined to form the products is represented by balanced chemical equation. If the heat is denoted by $q$ then the numerical value of $q$ depends on the manner in which
the reaction is performed for two methods of conducting chemical reactions in calorimeters.

The heat of combustion of maltose at a constant volume in the above question if water vapour is not condensed will be:

• A. -1350 kcal/mol
• B. -1343 kcal/mol
• C. -1370 kcal/mol
• D. -1400 kcal/mol

Answer 1

The correct option is B -1343 kcal/mol

$q=\Delta E+P\Delta V$ or $q=\Delta E+\Delta n_{g}RT$
where $\Delta E=$ the heat of combustion in calorimeteric bomb.
Reaction:
$C_{12}{H}_{22}{O}_{11}\left(s\right)+12O_2\left(g\right)\to 12C{O}_2\left(g\right)+11H_{2}O\left(g\right)$
On putting values we get
$q=-1350+\frac{11\times 2\times 298}{1000}\approx -1343kcal/mol$