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Sulphuric Acid

Calculate the...

Question

Calculate the enthalpy of combustion of methyl alcohol at 298 K from the following data
Bond $C - H$ $C - O$ $O - H$ $O = O$ $C = O$
Bond Enthalpy ( kJ $m o l^{- 1}$ 414 351.5 464.5 494 711
Resonance energy of $C O_{2} = - 143 k J m o l^{- 1}$
Latent heat of vaporisation of methyl alcohol $= 35.5 k J m o l^{- 1}$
Latent heat of vaporisation of water $= 40.6 k J m o l^{- 1}$

A

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

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B

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

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C

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

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D

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

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Solution

The correct option is B $- 136.7 k J m o l^{- 1}$
$C H_{3} O H (l) \to C H_{3} O H (g) Δ H_{1} = 35.5 k J / m o l$
$C H_{3} O H (g) + 2 O_{2} \to C O_{2} + 2 H_{2} O$

The bond energy of reactants
$= 3 H_{C_{H}} + H_{C - O} + H_{O - H} + 2 H_{O = O}$
$= 3 (414) + 351.5 + 464.5 + 2 (494)$
$= 3046 k J / m o l$

The bond energy of products
$= 2 H_{C = O} - resonance energy of C O_{2} + 4 H_{O_{H}}$
$= 2 (711) - 143 + 4 (464.5)$
$= 3137 k J / m o l$

The energy change for the combustion of methanol vapours $= Δ H_{2} = 3046 - 3137$
$= - 91 k J / m o l$

The latent heat of vaporisation of water is $40.6$ kJ/mol.
For $2$ moles of water, $Δ H_{3} = 2 \times 40.6$
$= 81.2 k J / m o l$

The enthalpy of combustion of methyl alcohol at $298$ K is
$Δ H = Δ H_{1} + Δ H_{2} - Δ H_{3}$
$Δ H = 35.5 - 91 - 81.2$
$= - 136.7 k J / m o l$

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Similar questions

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. 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. 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. 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 in their standard states:

H, 218 k J / m o l

C, 715 k J / m o l

O, 249 k J / m o l

.
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C - H = 415 k J / m o l

C - O = 365 k J / m o l

O - H = 463 k J / m o l

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Q. The enthalpy of combustion of

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^{- 1}

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