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Chapter 6: Problem 71

Which of the following does not have \(\Delta H_{\mathrm{f}}^{\circ}=0\) at \(25^{\circ} \mathrm{C} ?\) \(\begin{array}{lllll}\text { He }(g) & \text { Fe }(s) & \text { Cl }(g) & \text { S }_{8}(s) & \text { O }_{2}(g) & \text { Br }_{2}(l)\end{array}\)

Short Answer

Expert verified
The given item that does not have a standard enthalpy of formation of zero is Cl(g) due to its incorrect standard state.

Step by step solution

01

Identify the Standard State Elements

The standard state of an item is its phase (solid, liquid, or gas) at 25°C and 1 atm pressure. The standard states for helium (He), iron (Fe), chlorine (Cl), sulfur (S), oxygen (O), and bromine (Br) are He(g), Fe(s), Cl2(g), S8(s), O2(g), and Br2(l) respectively.
02

Identify the Incorrect Standard State

From the given options, Cl(g) is the only item that is not in its standard state. The standard state of Chlorine at 25°C and 1 atm pressure is Cl2(g), not Cl(g).

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