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Natural and Man-made Chemical Changes

The enthalpy ...

Question

The enthalpy of reaction for the reaction:

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l)$ is
$Δ_{r} H^{o} = - 572 k J m o l^{- 1}$

What will be standard enthalpy of formation of $H_{2} O (l)$ ?

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Solution

The standard enthalpy of formation of $H_{2} O (l)$ can be obtained by considering the following reaction:

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

As $Δ_{f} H^{o}$ is related to one mole of a compound formed at standard conditions

For the given reaction:

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l)$
the standard enthalpy of reaction is $Δ H_{r}^{o} = - 572 k J m o l^{- 1}$ ,

So, on relating the given equation with earlier equation, the half of $Δ H_{r}^{o}$ will be the standard molar enthalpy of formation;

$Δ_{f} H^{o} = \frac{1}{2} \times Δ H_{r}^{o}$

$= (\frac{- 572}{2}) k J m o l^{- 1}$

$Δ_{f} H^{o} = - 286 k J m o l^{- 1}$

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Similar questions

Q. The enthalpy of formation of reaction :

2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l) i s Δ_{r} H^{o} = - 572 k J m o l^{- 1}

What will be the enthalpy of formation of

H_{2} O (l)

?

Q. Determine enthalpy of formation for

H_{2} O_{2} (l),

using the listed enthalpies of reactions:

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

△_{r} H_{1}^{o} = - 818 k J / m o l

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

△_{r} H_{2}^{o} = - 622 k J / m o l

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); △_{f} H_{3}^{o} = - 285 k J / m o l

Q. Change in enthalpy for the reaction,

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

, if heat of formation of

H_{2} O_{2} (l)

H_{2} O (l)

- 188

- 286 k J / m o l

respectively is:

Q. The enthalpy of formation of reaction :

2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l) i s Δ_{r} H^{o} = - 572 k J m o l^{- 1}

What will be the enthalpy of formation of

H_{2} O (l)

?

Δ H_{f}^{0}

H_{2} O_{2}

H_{2} O

are -188 kJ/mol and -286 kJ/mol. What will be the enthalpy change of the reaction:

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

?

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Natural and Man-made Chemical Changes

Standard VIII Chemistry

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