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The surface of copper gets tarnished by ...

The surface of copper gets tarnished by the formation of copper oxide. gas was passed to prevent the oxide formation during heating of copper at 1250 K. However, the gas contains 1 mole % of water vapour as impurity. The water vapour oxidises copper as per the reaction given below :
`2Cu (s) + H_(2)O(g) rarr Cu_(2)O(s) + H_(2)(g)`
`p_(H_2)` is the minimum partial pressure of `H_(2)` (in bar) needed to prevent the oxidation at 1250 K. The value of 1n`(p_(H_2))` is _______.
(Given: total pressure = 1 bar), R (universal gas constant) = `8 JK^(-1)mol^(-1) , 1n(10) = 2.3 . Cu(s)` and `Cu_(2)O(s)` are mutually immiscible.
At `1250 K: 2Cu(s) + 1/2 O_(2)(g) rarr Cu(s) + 1/2 O_(2)(g) rarr Cu_(2)O(s), " '' DeltaG^(-) = -78000 J mol^(-1)`
`H_(2)(g) + 1/2 O_(2)(g) rarr H_(2)O (g), " "DeltaG^(-) = -178000 J mol^(-1), ("G is the Gibbs energy")`.

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The correct Answer is:
`-14.6`
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The surface of copper gets tarnished by the formation of copper oxide. N_(2) gas was passed to prevent the oxide formation during heating of copper at 1250 K. However, the N_(2) gas contains 1 mole % of water vapour as impurity. The water vapour oxidises copper as per the reaction given below: 2Cu(s) + H_(2)O(g) rarr Cu_(2)O(s) + H_(2)(g) is the minimum partial pressure of H2 (in bar) needed to prevent the oxidation at 1250 K. The value of ln is ____. (Given: total pressure = 1 bar, R (universal gas constant) = 8 J K−1 mol^(−1), ln(10) = 2.3. Cu(s) and Cu_(2)O(s) are mutually immiscible. At 1250 K: 2Cu(s) + 1//2 O_(2)(g) rarr Cu_(2)O(s) triangle H^(theta) = − 78,000 J mol^(−1) H_(2)(g) + 1//2 O_(2)(g) rarr H_(2)O(g), triangle G^(theta) = − 1,78,000 J mol^(−1) , G is the Gibbs energy

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