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Heat of Reaction

Given, C grap...

Question

Given, $C_{(g r a p h i t e s)} + O_{2} (g) \to C O_{2} (g)$
$Δ_{r} H^{\circ} = - 393.5 k J m o l^{- 1}$
$H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l);$
$Δ_{r} H^{\circ} = - 285.8 k J m o l^{- 2}$
$C O_{2} (g + 2 H_{2} O (l) \to C H_{4} (g) + 2 O_{2} (g)$
$Δ_{r} H^{\circ} = + 890.3 k J m o l^{- 1}$
Based on the above thermochemical equations, the value of $Δ_{r} H^{\circ}$ at 298K for the reaction, $C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)$ will be

A

+ 78.8 k J m o l^{(- 1)}

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B

+ 144.0 k J m o l^{(- 1)}

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C

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

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D

- 144.0 k J m o l^{(- 1)}

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Solution

The correct option is C $- 74.8 k J m o l^{(- 1)}$
Based on given $Δ_{r} H^{\circ}$
$Δ_{f} H^{\circ} = H_{C O_{2}}^{\circ} = - 393.5 k J m o l^{- 1}$ . . . . (i)
$Δ_{f} H^{\circ} = H_{(H_{2} O)}^{\circ} = - 285.8 k J m o l^{- 1}$ . . . . (ii)
$Δ_{f} H^{\circ} = H_{O_{2}}^{\circ} = 0.00 (e l e m e n t s)$
Required thermal reaction is for $Δ_{f} H^{\circ} o f (C H_{4})$
Thus, from III
$890.3 = [Δ_{f} H^{\circ} (C H_{4}) + 2 Δ_{f} H^{\circ} (O_{2})]$
$- [Δ_{f} H^{\circ} (C O_{2}) + 2 Δ_{f} H^{\circ} (H_{2} O)]$
$= Δ_{f} H^{\circ} (C H_{4}) + 0 - [- 393.5 - 2 \times 285.5]$
$∴ Δ_{f} H^{\circ} (C H_{4}) = - 74.8 k J / m o l$

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Similar questions

C_{(g r a p h i t e)} + O_{2} (g) \to C O_{2} (g);

Δ_{f} H^{\circ} = - 393.5 k J m o l^{- 1}

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

Δ_{f} H^{\circ} = - 285.8 k J m o l^{- 1}

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

Δ_{f} H^{\circ} = + 890.3 k J m o l^{- 1}

Based on the above thermochemical equations, the value of

Δ_{f} H^{\circ}

at 298 K for the reaction

C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)

C_{(g r a p h i t e)} + O_{2} (g) \to C O_{2} (g); Δ_{r} H^{o} = - 393.5 k J m o l^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ_{r} H^{o} = - 285.8 k J m o l^{- 1}

C O_{2} (g) + 2 H_{2} O (l) \to C H_{4} (g) + 2 O_{2} (g); Δ_{r} H^{o} = + 890.3 k J m o l^{- 1}

Based on the above thermochemical equations, the value of

Δ_{r} H^{o}

298 K

for the reaction

C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)

C_{(g r a p h i t e} + O_{2} (g) \to C O_{2} (g); Δ_{r} H^{o} = - 393.5 k J m o l^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ_{r} H^{o} = - 285.8 k J m o l^{- 1}

C O_{2} (g) + 2 H_{2} O (l) \to C H_{4} (g) + 2 O_{2} (g); Δ^{r} H 6 o = + 890.3 k J m o l^{- 1}

Based on the above thermochemical wquations, the value of

D e l t a_{r} H^{o}

298 K

for the reaction,

C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)

C_{(g r a p h i t e s)} + O_{2} (g) \to C O_{2} (g)

Δ_{r} H^{\circ} = - 393.5 k J m o l^{- 1}

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

Δ_{r} H^{\circ} = - 285.8 k J m o l^{- 2}

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

Δ_{r} H^{\circ} = + 890.3 k J m o l^{- 1}

Based on the above thermochemical equations, the value of

Δ_{r} H^{\circ}

at 298K for the reaction,

C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)

C_{(g r a p h i t e)} + O_{2} (g) \to C O_{2} (g);

Δ_{f} H^{\circ} = - 393.5 k J m o l^{- 1}

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

Δ_{f} H^{\circ} = - 285.8 k J m o l^{- 1}

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

Δ_{f} H^{\circ} = + 890.3 k J m o l^{- 1}

Based on the above thermochemical equations, the value of

Δ_{f} H^{\circ}

at 298 K for the reaction

C_{(g r a p h i t e)} + 2 H_{2} (g) \to C H_{4} (g)

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