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Standard XII

Physics

Calorimetry

The enthalpy ...

Question

The enthalpy of combustion of methane, graphite and dihydrogen at $298 K$ are $- 890.3$ $k J {m o l}^{- 1}, - 393.5$ $k J {m o l}^{- 1}, - 285.8$ $k J {m o l}^{- 1}$ respectively. Enthalpy of formation of ${C H}_{4 (g)}$ will be:

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

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

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+ 74.8 k J {m o l}^{- 1}

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+ 52.26 k J {m o l}^{- 1}

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Solution

The correct option is A $- 74.8 k J {m o l}^{- 1}$
${C H}_{4} + 2 O_{2} ⟶ {C O}_{2} + 2 H_{2} O; Δ H_{1} = - 890 k J {m o l}^{- 1} . . . (i)$

$C + O_{2} ⟶ {C O}_{2}; Δ H_{2} = - 393.5 k J {m o l}^{- 1} . . . (i i)$

$2 H_{2} + O_{2} ⟶ 2 H_{2} O; Δ H_{3} = 2 \times (- 285.8) k J {m o l}^{- 1} . . . (i i i)$

Required reaction $\to C + 2 H_{2} ⟶ {C H}_{4 (g)}; Δ H_{f} = ?$

From equation $(i i)$ - $(i)$ + $(i i i)$

$Δ H_{f} = (- 393.5) + 890.3 + 2 (- 285.8) = - 74 k J {m o l}^{- 1}$
Hence option A is correct.

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Similar questions

The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, $- 890.3 k J m o l^{- 1} - 393.5 k J m o l^{- 1}$ , and $- 285.8 k J m o l^{- 1}$ respectively. Enthalpy of formation of $C H_{4 (g)}$ will be
(i) $- 74.8 k J m o l^{- 1}$
(ii) $- 52.27 k J m o l^{- 1}$
(iii) $+ 74.8 k J m o l^{- 1}$
(iv) $+ 52.26 k J m o l^{- 1}$

Q. The enthalpy of combustion of methane graphite and dihydrogen at

298 K

are

- 890.3

m o l^{- 1}

and

- 285.8

m o l^{- 1}

respectively. Enthalpy of formation of

C H_{4} (g)

will be:

Q. a) The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are

- 890.3 k J^{- 1}

- 393.5 k J^{- 1}

and

- 285.8 k J^{- 1}

respectively. Calculate the enthalpy of formation of

{C H}_{4} (g)

b) Write the relationship between Gibb's energy, equilibrium constant and change in enthalpy.

Q. Determine the enthalpy of the reaction

C_{3} H_{8} (g) + H_{2} (g) ⟶ C_{2} H_{6} (g) + C H_{4} (g)

25^{\circ} C

using the given heat of combustion values under standard conditions. The standard heat of formation of

C_{3} H_{8} (g)

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

Compound:	$H_{2} (g)$	$C H_{4} (g)$	$C_{2} H_{6} (g)$	$C (g r a p h i t e)$
$Δ H^{⊖} (k J m o l^{- 1}) :$	$- 285.8$	$- 890.0$	$- 1560.0$	$- 393.5$

The standard enthalpy of formation $(Δ_{f} H^{0})$ at 298K for methane, $C H_{4} (G)$ is 74.8kJmol $^{- 1}$ . The additional information required to determine the average energy for C-H bond formation would be

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The enthalpy of combustion of methane, graphite and dihydrogen at 298K are −890.3 kJmol−1,−393.5 kJmol−1,−285.8 kJmol−1 respectively. Enthalpy of formation of CH4(g) will be:

The enthalpy of combustion of methane, graphite and dihydrogen at $298 K$ are $- 890.3$ $k J {m o l}^{- 1}, - 393.5$ $k J {m o l}^{- 1}, - 285.8$ $k J {m o l}^{- 1}$ respectively. Enthalpy of formation of ${C H}_{4 (g)}$ will be: