Given the following standard free energies at \(25^{\circ} \mathrm{C}\), $$ \begin{array}{ll} \mathrm{N}_{2} \mathrm{O}_{5}(g) \longrightarrow 2 \mathrm{NO}(g)+\frac{3}{2} \mathrm{O}_{2}(g) & \Delta G^{\circ}=-59.2 \mathrm{~kJ} \\ \mathrm{NO}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}_{2}(g) & \Delta G^{\circ}=-35.6 \mathrm{~kJ} \end{array} $$ calculate \(\Delta G^{\circ}\) at \(25^{\circ} \mathrm{C}\) for the reaction $$ 2 \mathrm{NO}_{2}(g)+{ }_{2}^{1} \mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2} \mathrm{O}_{5}(g) $$

Short Answer

Expert verified
Question: Calculate the standard free energy change for the following reaction using the given data: Reaction: \(2\, \mathrm{NO}_2(g) + \frac{1}{2}\, \mathrm{O}_2(g) \longrightarrow \mathrm{N}_2\mathrm{O}_5(g)\) Given Data: 1. \(\mathrm{N}_{2} \mathrm{O}_{5}(g) \longrightarrow 2 \mathrm{NO}(g) + \frac{3}{2} \mathrm{O}_{2}(g)\) ; \(\Delta G^{\circ} = -59.2 \, \mathrm{kJ}\) 2. \(\mathrm{NO}(g) + \frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}_{2}(g)\) ; \(\Delta G^{\circ} = -35.6\, \mathrm{kJ}\) Answer: The standard free energy change (\(\Delta G^{\circ}\)) of the reaction \(2\, \mathrm{NO}_2(g) + \frac{1}{2}\, \mathrm{O}_2(g) \longrightarrow \mathrm{N}_2\mathrm{O}_5(g)\) at \(25^{\circ} \mathrm{C}\) is \(-12.0\) kJ.

Step by step solution

01

Write down the target reaction

We want to find \(\Delta G^{\circ}\) for the following reaction: $$ 2 \mathrm{NO}_{2}(g) + \frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2} \mathrm{O}_{5}(g) $$
02

Identify the equations to manipulate

We are given two reactions: $$ \begin{array}{ll} \mathrm{N}_{2} \mathrm{O}_{5}(g) \longrightarrow 2 \mathrm{NO}(g) + \frac{3}{2} \mathrm{O}_{2}(g) & \Delta G^{\circ} = -59.2 \mathrm{~kJ} \\ \mathrm{NO}(g) + \frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}_{2}(g) & \Delta G^{\circ} = -35.6 \mathrm{~kJ} \end{array} $$
03

Rearrange the first equation

Reverse the first reaction so that it aligns with the desired reaction: $$ 2 \mathrm{NO}(g) + \frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2}\mathrm{O}_{5}(g) $$ Remember that reversing a reaction also reverses the sign of \(\Delta G^{\circ}\): $$ \Delta G^{\circ} = 59.2 \mathrm{~kJ} $$
04

Multiply the second equation by 2

Multiply the second reaction by a factor of 2 so that we have the same number of \(\mathrm{NO}_2\) molecules on both sides of the desired reaction: $$ 2 \mathrm{NO}(g) + \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) $$ When multiplying a reaction, the value of \(\Delta G^{\circ}\) for that reaction must also be multiplied: $$ \Delta G^{\circ} = -71.2 \mathrm{~kJ} $$
05

Add the manipulated equations

Add the manipulated reactions together to get the desired reaction: $$ (2 \mathrm{NO}(g) + \frac{3}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2}\mathrm{O}_{5}(g)) + (2 \mathrm{NO}(g) + \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)) $$ $$ \Rightarrow 2\,\mathrm{NO}_2(g) + \frac{1}{2}\,\mathrm{O}_2(g) \longrightarrow \mathrm{N}_2\mathrm{O}_5(g) $$ As we add the reactions, we also add their \(\Delta G^{\circ}\) values: $$ \Delta G^{\circ}_{\text{total}} = 59.2 \mathrm{~kJ} - 71.2 \mathrm{~kJ} = -12.0 \mathrm{~kJ} $$
06

Conclusion

The standard free energy change (\(\Delta G^{\circ}\)) of the reaction $$ 2\,\mathrm{NO}_2(g) + \frac{1}{2}\,\mathrm{O}_2(g) \longrightarrow \mathrm{N}_2\mathrm{O}_5(g) $$ at \(25^{\circ} \mathrm{C}\) is \(-12.0\) kJ.

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Most popular questions from this chapter

Use the values for \(\Delta G_{i}^{o}\) in Appendix 1 to calculate \(K_{\text {ip }}\) for barium sulfate at \(25^{\circ} \mathrm{C}\). Compare with the value given in Chapter 16 .

Use standard entropies and heats of formation to calculate \(\Delta G_{i}^{\circ}\) at \(25^{\circ} \mathrm{C}\) for (a) cadmium(II) chloride (s). (b) methyl alcohol, \(\mathrm{CH}_{3} \mathrm{OH}(l)\). (c) copper(I) sulfide (s).

Use Table \(17.1\) to calculate \(\Delta S^{\circ}\) for each of the following reactions. (a) \(\mathrm{CO}(\mathrm{g})+2 \mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l)\) (b) \(\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g)\) (c) \(\mathrm{BaCO}_{3}(s) \longrightarrow \mathrm{BaO}(s)+\mathrm{CO}_{2}(g)\) (d) \(2 \mathrm{NaCl}(s)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{NaF}(s)+\mathrm{Cl}_{2}(g)\)

The overall reaction that occurs when sugar is metabolized is $$ \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(s)+12 \mathrm{O}_{2}(g) \longrightarrow 12 \mathrm{CO}_{2}(g)+11 \mathrm{H}_{2} \mathrm{O}(l) $$ For this reaction, \(\Delta H^{\circ}\) is \(-5650 \mathrm{~kJ}\) and \(\Delta G^{\circ}\) is \(-5790 \mathrm{~kJ}\) at \(25^{\circ} \mathrm{C}\). (a) If \(25 \%\) of the free energy change is actually converted to useful work, how many kilojoules of work are obtained when one gram of sugar is metabolized at body temperature, \(37^{\circ} \mathrm{C}\) ? (b) How many grams of sugar would a 120 -lb woman have to eat to get the energy to climb the Jungfrau in the Alps, which is \(4158 \mathrm{~m}\) high? \(\left(w=9.79 \times 10^{-3} \mathrm{mh}\right.\), where \(w=\) work in kilojoules, \(m\) is body mass in kilograms, and \(h\) is height in meters.)

Consider the reaction $$ \mathrm{N}_{2} \mathrm{O}(g)+\mathrm{NO}_{2}(g) \longrightarrow 3 \mathrm{NO}(g) \quad K=4.4 \times 10^{-19} $$ (a) Calculate \(\Delta G^{\circ}\) for the reaction at \(25^{\circ} \mathrm{C}\). (b) Calculate \(\Delta G_{i}^{\circ}\) for \(\mathrm{N}_{2} \mathrm{O}\) at \(25^{\circ} \mathrm{C}\).

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