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Heat of Formation

Compute the h...

Question

Compute the heat of formation of liquid methyl alcohol in kilojoules per mole using the following data.
The heat of vaporisation of liquid methyl alcohol = $38 k J / m o l$ .
The heats of formation of gaseous atoms from the elements is their standard states: $H, 218 k J / m o l$ ; $C, 713 k J / m o l$ ; $O, 249 k J / m o l$ .
Average bond energies: $C - H = 415 k J / m o l$ ; $C - O = 365 k J / m o l$ ; $O - H = 463 k J / m o l$ .

A

- 266 k J / m o l

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B

- 488 k J / m o l

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C

Zero

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D

- 356 k J / m o l

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Solution

The correct option is A $- 266 k J / m o l$
$C (s) + 2 H_{2} (g) + \frac{1}{2} O_{2} (g) \to C H_{3} O H (l); Δ H = ?$
So, $Δ H_{f} = [Δ H_{C (s) \to C (g)} + 2 Δ H_{H - H} + 1 / 2 Δ H_{O = O}] - [3 Δ H_{C - H} + Δ H_{C - O} + Δ H_{O - H} + Δ H_{v a p . C H_{3} O H}]$
For reactants;
Heat of atomisation of 1 mole of $C = 715 k J$
Heat of atomisation of 4 moles of $H = 4 \times 218 k J$
Heat of atomisation of 1 mole of $O = 249 k J$
For products:
Heat of formation of 3 moles of $C - H$ bonds = $- 3 \times 415 k J$
Heat of formation of 1 mole of $C - O$ bonds = $- 356 k J$
Heat of formation of 1 mole of $O - H$ bonds = $- 463 k J$
Heat of condenstation of 1 mole of $C H_{3} O H$ to liquid $= - 38 k J$
So, On adding, we get $Δ H$ of formation of $C H_{3} O H (l)$ :
$Δ H = 715 + (4 \times 218) + 249 - (3 \times 415) - 356 - 463 - 38$
$Δ H = - 266 k J / m o l$

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Similar questions

Q. Compute the heat of formation of liquid methyl alcohol in kilojoules per mole using the following data.
The heat of vaporisation of liquid methyl alcohol =

38 k J / m o l

.
The heats of formation of gaseous atoms from the elements is their standard states:

H, 218 k J / m o l

C, 713 k J / m o l

O, 249 k J / m o l

.
Average bond energies:

C - H = 415 k J / m o l

C - O = 365 k J / m o l

O - H = 463 k J / m o l

.

Q. Compute the enthalpy of formation of liquid methyl alcohol in kJ mol

^{- 1}

, using the following data.

Enthalpy of vaporisation of liquid

C H_{3} O H = 38

Enthalpy of formation of gaseous atoms from the elements in their standard states are

H \to 218

C \to 715

O \to 249

Average Bond energies

C - H \to 415

C - O \to 356

O - H \to 463

Q. Compute the heat of formation of liquid methyl alcohol (in kJ mol

^{- 1}

) using the following data. The heat of vaporisation of liquid methyl alcohol is 38 kJ mol

^{- 1}

The heat of formation of gaseous atoms from the elements in their standard states:

H =

^{- 1}

C = 715

^{- 1}

O = 249

^{- 1}

Average bond energies:

C - H = 415

^{- 1}

C - O = 356

^{- 1}

O - H = 463

^{- 1}

Q. What is the heat of formation of liquid methyl alcohol in

k J m o l^{- 1},

use the following data.
Heat of vaporization of liquid methyl alcohol =

38 k J m o l^{- 1}

.
Heat of formation of gaseous atoms from the elements in their standard states:

H = 218 k J m o l^{- 1}, C = 715 k J m o l^{- 1}, O = 249 k J m o l^{- 1}

Average bond energies :

C - H = 415 k J m o l^{- 1} C - O = 356 k J m o l^{- 1} O - H = 463 k J m o l^{- 1}

Q. What is the heat of formation of liquid methyl alcohol in

k J m o l^{- 1},

use the following data.
Heat of vaporization of liquid methyl alcohol =

38 k J m o l^{- 1}

.
Heat of formation of gaseous atoms from the elements in their standard states:

H = 218 k J m o l^{- 1}, C = 715 k J m o l^{- 1}, O = 249 k J m o l^{- 1}

Average bond energies :

C - H = 415 k J m o l^{- 1} C - O = 356 k J m o l^{- 1} O - H = 463 k J m o l^{- 1}

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