Heats of combustion of graphite and hydrogen at 300 K are − 400 kJmol − 1 and − | TestHub

Passage / Comprehension

Photosynthesis is a bio process by which plants make energy-rich molecules from low-energy molecules with the help of energy from sunlight. The photosynthesis of glucose can be represented as:→

$6 CO_{2} g) + 6 H_{2} O g) + h ν \to C_{6} H_{12} O_{6} (s) + 6 O_{2} (g)$

Electrochemical oxidation of glucose to $CO_{2}$ and $H_{2} O$ , which is the reverse of photosynthesis, is an important reaction and it can be used in the construction of a fuel cell. In a fuel cell, a working substance called fuel is electrochemically oxidized by $O_{2}$ .

$C_{6} H_{12} O_{6} + 6 H_{2} O \to 24 e^{-} + 24 H^{+} + 6 CO_{2}$

$6 O_{2} + 24 H^{+} + 24 e^{-} \to 12 H_{2} O$

Heats of combustion of graphite and hydrogen at 300 K are $- 400 kJmol^{- 1}$ and $- 275 kJmol^{- 1}$ respectively. If on combustion, 1 g of glucose releases 15 kJ of energy, calculate the heat of formation of glucose at 300 K .

Options:

Answer:

Solution:

$C_{6} H_{12} O_{6} (s) + 6 O_{2} (g) \to 6 CO_{2} (g) + 6 H_{2} O (l)$

$Δ_{re a c t i o n} H^{0} - 180 \times 15 - 2700 x x = \sum v_{1} (Δ_{F} H^{0})_{P} - \sum v_{2} (Δ_{F} H^{0})_{R} = 6 \times - 400 + 6 (- 275) - x = - 2400 - 1650 - x = 300 - 1650 = - 1350$

Chemistry - Thermochemistry Question with Solution | TestHub

Options:

Doubts & Discussion