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Chapter 17: Problem 6

On the basis of your experience, predict which of the following reactions are spontaneous. (a) \(\mathrm{CO}_{2}(s) \longrightarrow \mathrm{CO}_{2}(g)\) at \(25^{\circ} \mathrm{C}\) (b) \(\mathrm{NaCl}(s) \longrightarrow \mathrm{NaCl}(l)\) at \(25^{\circ} \mathrm{C}\) (c) \(2 \mathrm{NaCl}(s) \longrightarrow 2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g)\) (d) \(\mathrm{CO}_{2}(g) \longrightarrow \mathrm{C}(s)+\mathrm{O}_{2}(g)\)

Short Answer

Expert verified
Also, which ones are non-spontaneous and why?

Step by step solution

01

Reaction (a) Analysis

In this reaction, we have solid carbon dioxide (dry ice) converting into gaseous carbon dioxide. Intuitively, we can expect an increase in disorder (higher entropy) as the gas phase is more disordered than the solid phase.
02

Reaction (a) Predict and Explain Spontaneity

Based on our experience, we can predict that reaction (a) will be spontaneous at 25°C. This is because there is an increase in entropy as the solid converts into gas, which generally promotes spontaneity in a reaction.
03

Reaction (b) Analysis

In this reaction, we have solid sodium chloride converting into liquid sodium chloride. Going from a solid state to a liquid state usually leads to an increase in disorder (entropy), but we need to keep in mind that this change occurs at 25°C.
04

Reaction (b) Predict and Explain Spontaneity

It's necessary to consider the fact that the melting point of sodium chloride is around 801°C. Since the required temperature for this particular reaction is 25°C, we can predict that reaction (b) is non-spontaneous under these conditions.
05

Reaction (c) Analysis

In this reaction, we have solid sodium chloride breaking down into solid sodium and gaseous chlorine. It is important to note that sodium chloride is considered a stable compound with strong ionic bonds, resulting in low likelihood of easily breaking apart.
06

Reaction (c) Predict and Explain Spontaneity

Given the strong ionic bonds of sodium chloride, the overall stability of the compound, and the need to break those bonds to form the products, we can predict that reaction (c) is non-spontaneous under normal conditions.
07

Reaction (d) Analysis

In this reaction, we have gaseous carbon dioxide breaking down into solid carbon and gaseous oxygen. Similar to reaction (c), carbon dioxide is a stable compound, and breaking it down would require a significant amount of energy.
08

Reaction (d) Predict and Explain Spontaneity

Considering the stability of carbon dioxide and the energy required to break it down into its components, we can predict that reaction (d) is non-spontaneous under normal conditions.

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Most popular questions from this chapter

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.)

I Sodium carbonate, also called "washing soda," can be made by heating sodium hydrogen carbonate: $$ \begin{gathered} 2 \mathrm{NaHCO}_{3}(s) \longrightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \\ \Delta H^{\circ}=+135.6 \mathrm{~kJ} ; \Delta G^{\circ}=+34.6 \mathrm{~kJ} \text { at } 25^{\circ} \mathrm{C} \end{gathered} $$ (a) Calculate \(\Delta S^{\circ}\) for this reaction. Is the sign reasonable? (b) Calculate \(\Delta G^{\circ}\) at \(0 \mathrm{~K} ;\) at \(1000 \mathrm{~K}\).

How many moles of ATP must be converted to ADP by the reaction \(\mathrm{ATP}(a q)+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{ADP}(a q)+\mathrm{HPO}_{4}^{2-}(a q)+2 \mathrm{H}^{+}(a q)\) $$ \Delta G^{\circ}=-31 \mathrm{~kJ} $$ to bring about a nonspontaneous biochemical reaction in which \(\Delta G^{\circ}=+372 \mathrm{~kJ}\) ?

Calculate \(\Delta G^{\circ}\) at \(45^{\circ} \mathrm{C}\) for reactions for which (a) \(\Delta H^{\circ}=293 \mathrm{~kJ} ; \Delta S^{\circ}=-695 \mathrm{~J} / \mathrm{K}\) (b) \(\Delta H^{\circ}=-1137 \mathrm{~kJ} ; \Delta S^{\circ}=0.496 \mathrm{~kJ} / \mathrm{K}\) (c) \(\Delta H^{\circ}=-86.6 \mathrm{~kJ} ; \Delta S^{\circ}=-382 \mathrm{~J} / \mathrm{K}\)

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) \(2 \mathrm{NaCl}(s)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{NaF}(s)+\mathrm{Cl}_{2}(g)\)
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