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Thermal Energy

Consider the ...

Question

Consider the following reactions :
I) $H^{+} (a q) + O H^{-} (a q) = H_{2} O (l); Δ H = - X_{1} k J . m o l^{- 1}$
II) $H_{2} (g) + \frac{1}{2} O_{2} (g) = H_{2} O (l); Δ H = - X_{2} k J . m o l^{- 1}$
III) $C O_{2} (g) + H_{2} (g) = C O (g) + H_{2} O (l); Δ H = + X_{3} k J . m o l^{- 1}$
IV) $C_{2} H_{2} (g) + \frac{5}{2} O_{2} (g) = 2 C O (g) + H_{2} O (l); Δ H = + X_{4} k J . m o l^{- 1}$
Enthalpy of formation of $H_{2} O (l)$ is:

A

+ X_{1} k J . m o l^{- 1}

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B

- X_{2} k J . m o l^{- 1}

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C

+ X_{3} k J . m o l^{- 1}

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D

+ X_{4} k J . m o l^{- 1}

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Solution

The correct option is A $- X_{2} k J . m o l^{- 1}$
The standard enthalpy change of formation of a compound is the enthalpy change which occurs when one mole of the compound is formed from its elements under standard conditions. The equation showing the standard enthalpy change of formation of water is
$H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l)$
$↑$
$1$ mole of water formed.
$∴$ Enthalpy of formation is $- X_{2} k J / m o l$ .

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Similar questions

Q. Consider the following reactions.

H_{(a q)}^{+} + O H_{(a q)}^{-} = H_{2} O_{(l)}, Δ H = - X_{1}

m o l^{- 1}

H_{2 (g)} + \frac{1}{2} O_{2 (g)} = H_{2} O_{(l)}, Δ H = X_{2}

m o l^{- 1}

C O_{2 (g)} + H_{2 (g)} = C O_{(g)} + H_{2} O_{(l)} - X_{3}

m o l^{- 1}

C_{2} H_{2 (g)} + \frac{5}{2} O_{2 (g)} = 2 C O_{2 (g)} + H_{2} O_{(l)} + X_{4}

m o l^{- 1}

Enthalpy of formation of

H_{2} O_{(l)}

Q. Consider the following reactions:

(i) H^{+} (a q) + O H^{-} (a q) \to H_{2} O (l), Δ H = - X_{1} {kJ mol}^{- 1}

(i i) H_{2} (g) + \frac{1}{2} O_{2} (a q) \to H_{2} O (l), Δ H = - X_{2} {kJ mol}^{- 1}

(i i i) C O_{2} (g) + H_{2} (g) \to C O (g) + H_{2} O (l), Δ H = - X_{3} {kJ mol}^{- 1}

(i v) C_{2} H_{2} (g) + \frac{5}{2} O_{2} (g) \to 2 C O_{2} (g) + H_{2} O (l), Δ H = X_{4} {kJ mol}^{- 1}

Enthalpy of formation of

H_{2} O (l)

H_{2} O (l) \to H^{+} (a q) + O H^{-} (a q); Δ H = 57.32 k J

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ H = - 286.02 k J

Then, calculate the enthalpy of formation of

O H^{-}

25^{o} C

;

H_{2} O (l) \to H^{+} (a q) + O H^{-} (a q); Δ H = 57.32

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ H = - 286.02

Then calculate the enthalpy of formation of

O H^{-}

25^{o}

Q. On the basis of the following thermochemical data:

(Δ_{f} G^{0} (H)_{(a q)}^{+} = 0)

H_{2} O (l) ⟶ H^{+} (a q) + O H^{-} (a q); Δ H = 57.32 k J

H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l); Δ H = - 286.20 k J

The value of enthalpy of formation of

O H^{-}

25^{o} C

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