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Chapter 6: Problem 45

Which of the following standard enthalpy of formation values is not zero at \(25^{\circ} \mathrm{C} ? \mathrm{Na}(s), \operatorname{Ne}(g)\) \(\mathrm{CH}_{4}(g), \mathrm{S}_{8}(s), \mathrm{Hg}(l), \mathrm{H}(g)\)

Short Answer

Expert verified
The standard enthalpy of formation for \( \mathrm{CH}_{4}(g) \) and \( \mathrm{H}(g) \) are not zero at 25 Celsius.

Step by step solution

01

Analysis of given compounds

Observe the given elements and their states: Sodium (Na) solid, Neon (Ne) gas, Methane (CH4) gas, Sulfur (S8) solid, Mercury (Hg) liquid, and Hydrogen (H) gas.
02

Distinguish elemental states

There are six given elements and compounds. The first thing we need to do is distinguish them, and analyze their physical states: Sodium (Na) is a solid in its standard state, Neon (Ne) is a gas in its standard state, Methane CH4 is not an element but a compound, Mercury (Hg) is a liquid in its standard state, Sulfur (S8) is a solid in its standard state and Hydrogen (H) is a diatomic gas \(H_{2}\) in its standard state, not a mono-atomic gas.
03

Correct answer

From given elements and compounds, only Methane (CH4) and Hydrogen (H) are not in their standard states at 25 degrees Celsius and 1 atmosphere of pressure. Methane (CH4) is a compound, and its standard enthalpy of formation is not zero. For Hydrogen (H), its standard state should be H2, not H (monoatomic). Thus, the answer is Methane (CH4) and Hydrogen (H), which do not have zero standard enthalpy of formation at 25 degrees Celsius and 1 atmosphere of pressure.

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