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Heat of Formation

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Question

Calculate the enthalpy of formation of $Δ H_{f}$ for $C_{2} H_{5} O H$ from tabulated data and its heat of combustion as represented by the following equations:
$H_{2} (g) + 1 / 2 O_{2} (g) ⟶ H_{2} O (g); Δ H^{o} = - 241.8 k J {m o l}^{- 1} . . . (i)$
$C (s) + O_{2} (g) ⟶ C O_{2} (g); Δ H^{o} = - 393.5 k J {m o l}^{- 1} . . . (i i)$
$C_{2} H_{5} O H (l) + 3 O_{2} (g) ⟶ 3 H_{2} O (g) + 2 C O_{2} (g); Δ H^{o} = - 1234.7 k J . . . (i i i)$

A

- 2747.1 k J {m o l}^{- 1}

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B

- 277.7 k J {m o l}^{- 1}

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C

- 277.7. k J {m o l}^{- 1}

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D

2747.1 k J {m o l}^{- 1}

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Solution

The correct option is B $- 277.7 k J {m o l}^{- 1}$
Required equation
$H_{2} (g) + 1 / 2 O_{2} (g) ⟶ C_{2} H_{5} O H (l)$
$2 C (s) + 2 O_{2} (g) ⟶ 2 C O_{2} (g); Δ H^{o} = 2 \times - 393.5 k J {m o l}^{- 1}$
${3 H}_{2} (g) + 1 / 3_{2} (g) ⟶ 3 H_{2} O (g); Δ H^{o} = 3 \times - 241.8 k J {m o l}^{- 1}$
$2 H_{2} O (l) + 2 C O_{2} (g) ⟶ C_{2} H_{5} O H (l) + 3 O_{2} (g); Δ H^{o} = + 1234.7 k J$
On adding
$2 C (s) + 3 H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ C_{2} H_{5} O H (l); Δ H^{o} = - 277.7 k J {m o l}^{- 1} .$

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Similar questions

Q. Calculate the standard enthalpy of formation of

C H_{3} O H (l)

from the following data.

C H_{3} O H (l) + \frac{3}{2} O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)

Δ H^{o} = - 726

m o l^{- 1}

+ O_{2} (g) \to C O_{2} (g);

Δ_{c} H^{0} = - 393

m o l^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l);

Δ_{t} H^{o} = - 286

m o l^{- 1}

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Q. Use the given standard enthalpies of formation to determine the heat of reaction of the following reaction:

C_{2} H_{5} O H (l) + 3 O_{2} (g) ⟶ 2 C O_{2} (g) + 3 H_{2} O (g)

Δ H_{f} C_{2} H_{5} O H (l) = - 277.7 k J / m o l e

Δ H_{f} C O_{2} (g) = - 393.5 k J / m o l e

Δ H_{f} H_{2} O (g) = - 241.8 k J / m o l e

Q. Calculate the enthalpy of formation of ethyl alcohol from the following data:

C_{2} H_{5} O H (l) + 3 O_{2} (g) \to 2 C O_{2} (g) + 3 H_{2} O (l)

Δ_{r} H^{\circ} = - 1368.0 k J

C (s) + O_{2} (g) \to C O_{2} (g)

Δ_{r} H^{\circ} = - 393.5 k J

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l)

Δ_{r} H^{\circ} = - 286.0 k J

Q. Calculate enthalpy for formation of ethylene from the following data:

C (g r a p h i t e) + O_{2} (g) \to C O_{2} (g); Δ H = - 393.5 k J

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ H = - 286.2 k J

C_{2} H_{4} (g) + 3 O_{2} (g) \to 2 C O_{2} (g) + 2 H_{2} O (l); Δ H = - 1410.8 k J

Q. From the data at

25^{o} C

:

{F e}_{2} O_{3} (s) + 3 C_{g r a p h i t e} ⟶ 2 F e (s) + 3 C O (g); Δ H^{o} = 492 k J / m o l

F e O (s) + C_{g r a p h i t e} ⟶ F e (s) + C O (g); Δ H^{o} = 155.8 k J / m o l

C_{g r a p h i t e} + O_{2} (g) ⟶ C O_{2} (g); Δ H^{o} = - 393.51 k J / m o l

C O (g) + \frac{1}{2} O_{2} (g) ⟶ C O_{2} (g); Δ H^{o} = - 282.98 k J / m o l

Calculate standard heats of formation of

F e O (s)

{F e}_{2} O_{3} (s)

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