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Chapter 6: Problem 98

For which of the following reactions does \(\Delta H_{\mathrm{rxn}}^{\circ}=\) \(\Delta H_{\mathrm{f}}^{\circ} ?\) (a) \(\mathrm{H}_{2}(g)+\mathrm{S}(\) rhombic \() \longrightarrow \mathrm{H}_{2} \mathrm{~S}(g)\) (b) C(diamond) \(+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)\) (c) \(\mathrm{H}_{2}(g)+\mathrm{CuO}(s) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{Cu}(s)\) (d) \(\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}(g)\)

Short Answer

Expert verified
The reactions for which \(\Delta H_{\mathrm{rxn}}^{\circ}= \Delta H_{\mathrm{f}}^{\circ}\) are (a) \(\mathrm{H}_{2}(g)+\mathrm{S}(\) rhombic $) \longrightarrow \mathrm{H}_{2}\mathrm{~S}(g)\)$ and (b) C(diamond) \(+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)\)

Step by step solution

01

Analyzing reaction (a)

\(\mathrm{H}_{2}(g)+\mathrm{S}(\) rhombic $) \longrightarrow \mathrm{H}_{2}\mathrm{~S}(g)\) - In this case, one mole of Hydrogen Sulfide is being formed from its elements in their standard states. Therefore, \(\Delta H_{\mathrm{rxn}}^{\circ}=\Delta H_{\mathrm{f}}^{\circ}\) for this reaction.
02

Analyzing reaction (b)

C(diamond) \(+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)\) - This reaction forms 1 mole of Carbon Dioxide from its elements in their standard states which signifies that for this reaction, \(\Delta H_{\mathrm{rxn}}^{\circ} = \Delta H_{\mathrm{f}}^{\circ}\).
03

Analyzing reaction (c)

\(\mathrm{H}_{2}(g)+\mathrm{CuO}(s) \longrightarrow \mathrm{H}_{2}\mathrm{O}(l)+\mathrm{Cu}(s)\) - In this reaction, water and copper are the products and not a single compound, so \(\Delta H_{\mathrm{rxn}}^{\circ}\) is different from \(\Delta H_{\mathrm{f}}^{\circ}\).
04

Analyzing reaction (d)

\(\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}(g)\) - In this reaction, the compound Ozone is being formed but the oxygen is not in its standard state which is O2(g) and not O(g). Therefore, \(\Delta H_{\mathrm{rxn}}^{\circ}\) is not equal to \(\Delta H_{\mathrm{f}}^{\circ}\).

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Most popular questions from this chapter

The internal energy of an ideal gas depends only on its temperature. Do a first-law analysis of this process. A sample of an ideal gas is allowed to expand at constant temperature against atmospheric pressure. (a) Does the gas do work on its surroundings? (b) Is there heat exchange between the system and the surroundings? If so, in which direction? (c) What is \(\Delta U\) for the gas for this process?

A 3.53-g sample of ammonium nitrate \(\left(\mathrm{NH}_{4} \mathrm{NO}_{3}\right)\) was added to \(80.0 \mathrm{~mL}\) of water in a constantpressure calorimeter of negligible heat capacity. As a result, the temperature of the water decreased from \(21.6^{\circ} \mathrm{C}\) to \(18.1^{\circ} \mathrm{C}\). Calculate the heat of solution \(\left(\Delta H_{\mathrm{soln}}\right)\) of ammonium nitrate.

Define these terms: enthalpy, enthalpy of reaction. Under what condition is the heat of a reaction equal to the enthalpy change of the same reaction?

An excess of zinc metal is added to \(50.0 \mathrm{~mL}\) of a \(0.100 M\) AgNO \(_{3}\) solution in a constant-pressure calorimeter like the one pictured in Figure \(6.9 .\) As a result of the reaction $$\mathrm{Zn}(s)+2 \mathrm{Ag}^{+}(a q) \longrightarrow \mathrm{Zn}^{2+}(a q)+2 \mathrm{Ag}(s)$$ the temperature rises from \(19.25^{\circ} \mathrm{C}\) to \(22.17^{\circ} \mathrm{C}\). If the heat capacity of the calorimeter is \(98.6 \mathrm{~J} /{ }^{\circ} \mathrm{C},\) calculate the enthalpy change for the above reaction on a molar basis. Assume that the density and specific heat of the solution are the same as those for water, and ignore the specific heats of the metals.

What are the units for energy commonly employed in chemistry?
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