Question

how many of the following elements, labeled i-v, in the state shown, has \\( \delta h_{f}^{\circ}=0 \\)?
i. \\( i_{2}(s) \\)
ii. c (graphite)
iii. fe(s)
iv. hg(l)
v. xe(g)
a. 2 b. 1 c. 5 d. 3 e. 4

Explanation:

Step1: Recall the definition of standard enthalpy of formation ($\Delta H_f^{\circ}$)

The standard enthalpy of formation of an element in its standard state is zero. The standard state of an element is its most stable form at 1 atm pressure and 298 K.

Step2: Analyze each element

• For \(I_2(s)\): Solid iodine (\(I_2(s)\)) is the standard state of iodine. So, \(\Delta H_f^{\circ}(I_2(s)) = 0\).
• For \(C(graphite)\): Graphite is the standard state of carbon. So, \(\Delta H_f^{\circ}(C(graphite)) = 0\).
• For \(Fe(s)\): Solid iron (\(Fe(s)\)) is the standard state of iron. So, \(\Delta H_f^{\circ}(Fe(s)) = 0\).
• For \(Hg(l)\): Liquid mercury (\(Hg(l)\)) is the standard state of mercury. So, \(\Delta H_f^{\circ}(Hg(l)) = 0\).
• For \(Xe(g)\): Gaseous xenon (\(Xe(g)\)) is the standard state of xenon (noble gas). So, \(\Delta H_f^{\circ}(Xe(g)) = 0\).

Answer:

C. 5