Question

The heat of combustion of sucrose, C₁₂H₂₂O₁₁(s) at constant volume is – 1348.9 kcal mol^–1 at 25°C, then the heat of reaction at constant pressure, when steam is produced , is

• A. – 1342.344 kcal
• B.
  • 1342.344 kcal
• C.
  • 1250 kcal
• D. None

Answer 1

Answer: (A)

– 1342.344 kcal

Answer 2

The combustion equation of sucrose is

C₁₂H₂₂O₁₁(s) + 12O₂(g) → 12CO₂(g) + 11H₂O (g)

Here,

∆n = sum of gaseous product moles – sum of gaseous reactant moles

∆n = 12 + 11 – 12

∆n = 11

As we Know

∆H = ∆E + ∆n RT, Where ∆H = heat of reaction at constant pressure

∆E = heat of reaction at constant volume

Here, ∆E = – 1348.9 kcal

R = 2.0 cal, T = 25+273 = 298 K

∴∆H = (–1348.9 × 1000) + 11× 2 × 298

= – 1348900 + 6556 = – 1342344 cal

= – 1342.344 kcal