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Chapter 6: Problem 123

Which of the following substances have an enthalpy of formation equal to zero? a. \(\mathrm{Cl}_{2}(g)\) b. \(\mathrm{H}_{2}(g)\) c. \(\mathrm{N}_{2}(l)\) d. \(\mathrm{Cl}(g)\)

Short Answer

Expert verified
The substances with an enthalpy of formation equal to zero are \(\mathrm{Cl}_{2}(g)\) and \(\mathrm{H}_{2}(g)\), as they are in their standard states at 1 atm pressure and 298.15 K.

Step by step solution

01

Identify the standard states of the given substances

Identify the substances listed and determine the standard states of their constituent elements. This involves looking at periodic table or reference material to find the most stable state these elements exist in at standard conditions.
02

Compare the given substances to their standard states

Determine which substances are in their standard states. If a substance is in its standard state, its enthalpy of formation would be zero.
03

Identify the substances with enthalpy of formation equal to zero

Based on the comparison in Step 2, list the substances that have an enthalpy of formation equal to zero. Substance a. \(\mathrm{Cl}_{2}(g)\) - In its standard state, Chlorine exists as a diatomic gas. So, this is in its standard state. b. \(\mathrm{H}_{2}(g)\) - In its standard state, Hydrogen exists as a diatomic gas. So, this is in its standard state. c. \(\mathrm{N}_{2}(l)\) - In its standard state, Nitrogen exists as a diatomic gas. This is not in its standard state, as this is a liquid. d. \(\mathrm{Cl}(g)\) - In its standard state, Chlorine exists as a diatomic gas. This is not in its standard state, as this is a monoatomic gas.
04

Conclusion

Based on our analysis, the substances with an enthalpy of formation equal to zero are \(\mathrm{Cl}_{2}(g)\) and \(\mathrm{H}_{2}(g)\). These are the substances that are in their standard state at 1 atm pressure and 298.15 K.

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Most popular questions from this chapter

When \(1.00 \mathrm{~L}\) of \(2.00 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}\) solution at \(30.0^{\circ} \mathrm{C}\) is added to \(2.00 \mathrm{~L}\) of \(0.750 \mathrm{M} \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) solution at \(30.0^{\circ} \mathrm{C}\) in a calorimeter, a white solid \(\left(\mathrm{BaSO}_{4}\right)\) forms. The temperature of the mixture increases to \(42.0^{\circ} \mathrm{C}\). Assuming that the specific heat capacity of the solution is \(6.37 \mathrm{~J} /{ }^{\circ} \mathrm{C} \cdot \mathrm{g}\) and that the density of the final solution is \(2.00 \mathrm{~g} / \mathrm{mL}\), calculate the enthalpy change per mole of \(\mathrm{BaSO}_{4}\) formed.

A piston performs work of \(210 . \mathrm{L} \cdot \mathrm{atm}\) on the surroundings, while the cylinder in which it is placed expands from \(10 . \mathrm{L}\) to \(25 \mathrm{~L}\). At the same time, \(45 \mathrm{~J}\) of heat is transferred from the surroundings to the system. Against what pressure was the piston working?

A swimming pool, \(10.0 \mathrm{~m}\) by \(4.0 \mathrm{~m}\), is filled with water to a depth of \(3.0 \mathrm{~m}\) at a temperature of \(20.2^{\circ} \mathrm{C}\). How much energy is required to raise the temperature of the water to \(24.6^{\circ} \mathrm{C} ?\)

On Easter Sunday, April 3,1983, nitric acid spilled from a tank car near downtown Denver, Colorado. The spill was neutralized with sodium carbonate: \(2 \mathrm{HNO}_{3}(a q)+\mathrm{Na}_{2} \mathrm{CO}_{3}(s) \longrightarrow 2 \mathrm{NaNO}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l)+\mathrm{CO}_{2}(g)\) a. Calculate \(\Delta H^{\circ}\) for this reaction. Approximately \(2.0 \times\) \(10^{4}\) gal nitric acid was spilled. Assume that the acid was an aqueous solution containing \(70.0 \% \mathrm{HNO}_{3}\) by mass with a density of \(1.42 \mathrm{~g} / \mathrm{cm}^{3} .\) What mass of sodium carbonate was required for complete neutralization of the spill, and what quantity of heat was evolved? ( \(\Delta H_{\mathrm{f}}^{\circ}\) for \(\left.\mathrm{NaNO}_{3}(a q)=-467 \mathrm{~kJ} / \mathrm{mol}\right)\) b. According to The Denver Post for April 4,1983 , authorities feared that dangerous air pollution might occur during the neutralization. Considering the magnitude of \(\Delta H^{\circ}\), what was their major concern?

The enthalpy of combustion of solid carbon to form carbon dioxide is \(-393.7 \mathrm{~kJ} / \mathrm{mol}\) carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is \(-283.3 \mathrm{~kJ} /\) mol CO. Use these data to calculate \(\Delta H\) for the reaction $$ 2 \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}(g) $$
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