At constant volume at 27-C- 2C6H6g -15O2 g - 12CO2g-6H2Ol- - u-1600 kcal 2C2H2g -5O2 g - 4CO2g-2H2Ol- - u-620 kcalCalculate the heat of polymerisation of acetylene to benzene at constant pressure-

(1) 2C_6H_6 (g) +15O_2(g) → 12 CO_2(g) + 6H_2O(l); Δ E_1= 162 kcal(2) 2C_2H_2 (g) +5O_2(g) → 4CO_2(g) + 2H_2O(l); Δ E_2= 620 kcal 3× (2) (1) ⟹ 6 ...

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Standard XII

Physics

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At constant v...

Question

At constant volume at $27^{\circ} C$ ,
$2 C_{6} H_{6} (g) + 15 O_{2} (g) \to 12 C O_{2} (g) + 6 H_{2} O (l); Δ u = - 1600 k c a l$
$2 C_{2} H_{2} (g) + 5 O_{2} (g) \to 4 C O_{2} (g) + 2 H_{2} O (l); Δ u = - 620 k c a l$
Calculate the heat of polymerisation of acetylene to benzene at constant pressure.

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Solution

(1) $2 C_{6} H_{6} (g) + 15 O_{2} (g) \to 12 C O_{2} (g) + 6 H_{2} O (l); Δ E_{1} = - 162$ kcal

(2) $2 C_{2} H_{2} (g) + 5 O_{2} (g) \to 4 C O_{2} (g) + 2 H_{2} O (l); Δ E_{2} = - 620$ kcal

$3 \times (2) - (1) ⟹ 6 C_{2} H_{2} (g) \to 2 C_{6} H_{6} (g)$
$Δ E = 3 Δ E_{2} - E_{1}$

$= - 1860 + 1600 = - 260$ kcal
$∴ 3 C_{2} H_{2} (g) \to C_{6} H_{6} (g), Δ E = \frac{- 260}{2} = - 130$ Kcal

$∴ Δ H = Δ E + Δ n R T$

$= - 180 K c a l + (1 - 3) \times 1.98 \times 10^{- 3} \times 300$

$= - 180 - 2 \times 0.198 \times 3 = - 130 - 1.188 = - 131.188$ Kcal

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At constant volume at 27∘C,2C6H6(g)+15O2(g)→12CO2(g)+6H2O(l);Δu=−1600kcal2C2H2(g)+5O2(g)→4CO2(g)+2H2O(l);Δu=−620kcalCalculate the heat of polymerisation of acetylene to benzene at constant pressure.