Consider the following data: Heat of combustion of H 2 (g) = - 241.8 kJ mol - 1 Heat of combustion of C(g) = - 393.5 kJ mol - 1 Heat of combustion of C 2 H 5 OH(l) = - 1234.7 kJ mol - 1 The heat of formation of C 2 H 5 OH ( l ) is (-) ________ kJ m

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Solution

Q.
Consider the following data:

${Heat of combustion of H}_{2} (g) = - {241.8 kJ mol}^{- 1}$

$Heat of combustion of C(g) = - {393.5 kJ mol}^{- 1}$

${Heat of combustion of C}_{2} H_{5} OH(l) = - {1234.7 kJ mol}^{- 1}$

The heat of formation of $C_{2} H_{5} OH (l)$ is (-) ________ kJ ${mol}^{- 1}$ (Nearest Integer) [2023]

Ans.
(278)

$2 C (s) + 3 H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ C_{2} H_{5} OH Δ H = ?$

$given$

$(i) C (s) + O_{2} (g) ⟶ {CO}_{2} (g) Δ H_{1} = - 393.5 kJ/mol$

$(ii) H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l) Δ H_{2} = - 241.8 kJ/mol$

$(iii) C_{2} H_{5} OH + 3 O_{2} (g) ⟶ 2 {CO}_{2} (g) + 3 H_{2} O Δ H = - 1234.7 kJ/mol$

$Required equation = 2 \times eq. (i) + 3 \times eq. (ii) - eq. (iii)$

$= 2 (- 393.5) + 3 (- 241.8) - (- 1234.7)$

$= - 278 kJ/mol$

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