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Gibbs Free Energy & Spontaneity

Silane, SiH 4...

Question

Silane, $S i H_{4}$ like methane, burns in air. The product silica (silicon dioxide) is solid quite unlike carbondioxide.
$S i H_{4 (g)} + 2 O_{2 (g)} \to S i O_{2} (s) + 2 H_{2} O_{(g)}$ standard Gibbs energy of formation of $S i O_{2} (s)$ , $H_{2} O$ and $S i H_{4}$ are 805, – 228.6 and + 52.3 (all is KJ $m o l^{- 1}$ ) respectively. Calculate the value of $Δ_{r} G$ .

A

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B

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C

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D

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Solution

The correct option is A
Applying equation,
$Δ_{r} G^{\circ} = \sum V_{p} Δ_{f} G^{\circ} (p r o d u c t s) - \sum V_{p} Δ_{f} G^{\circ} (r e a c t a n t s)$
$= [Δ_{f} G^{\circ} (S i O_{2}) + 2 Δ_{f} G^{\circ} (H_{2} O)] - [Δ_{f} G^{\circ} (S i H_{4}) + 2 Δ_{f} G^{\circ} (O_{2})]$
Gibbs energy of formation of elements being zero, we have
$Δ_{r} G^{\circ} = [(805 K J m o l^{- 1}) + (- 228.6 K J m o l^{- 1})] - [1 (+ 52.3 K J m o l^{- 1}) + 0]$
$= - 1314.5 K J m o l^{- 1}$
Negative value of $Δ_{r} G^{\circ}$ supports spontaneity of the above reaction.

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Similar questions

S i H_{4}

like methane, burns in air. The product silica (silicon dioxide) is solid quite unlike carbondioxide.

S i H_{4 (g)} + 2 O_{2 (g)} \to S i O_{2} (s) + 2 H_{2} O_{(g)}

standard Gibbs energy of formation of

S i O_{2} (s)

H_{2} O

S i H_{4}

are 805, – 228.6 and + 52.3 (all is KJ

m o l^{- 1}

) respectively. Calculate the value of

Δ_{r} G

.

Q. What will be the amount of heat evolved by burning

10 L

of methane under standard conditions?
(Given heats of formation of

C H_{4}, C O_{2} a n d H_{2} O a r e - 76.2, - 398.8 a n d - 241.6 k J m o l^{- 1}

Q. The standard enthalpies of formation at 300 K for

C C l_{4} (l), H_{2} O (g), (C O_{2}) a n d H C l (g) a r e - 107, - 242, - 394 a n d - 93 k J m o l^{- 1},

respectively. The value of

△ U_{300}^{o}

for the reaction

C C l_{4} (l) + 2 H_{2} O (g) \to C O_{2} (g) + 4 H C l (g)

Q. The standard heats of formation of

{C H}_{4} (g), {C O}_{2} (g)

H_{2} O (g)

- 76.2, - 398.8

- 241.6

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

respectively. Calculate the amount of heat evolved by burning

1 m^{3}

of methane measured under normal conditions.

Q. Show that the reaction

C O (g) + \frac{1}{2} O_{2} (g) ⟶ C O_{2} (g)

300 K

is spontaneous and exothermic, when the standard entropy change is

- 0.094 k J m o l^{- 1} K^{- 1}

. The values of standard Gibbs free energy of formation of

C O_{2}

C O

- 394.4

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

, respectively.

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