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Chapter 17: Problem 46

Predict the sign of \(\Delta S^{\circ}\) for each of the following changes. a. $\mathrm{K}(s)+\frac{1}{2} \mathrm{Br}_{2}(g) \longrightarrow \mathrm{KBr}(s)$ b. $\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$ c. \(\mathrm{KBr}(s) \longrightarrow \mathrm{K}^{+}(a q)+\mathrm{Br}^{-}(a q)\) d. \(\mathrm{KBr}(s) \longrightarrow \mathrm{KBr}(l)\)

Short Answer

Expert verified
In summary, the signs of ΔS° for each reaction are as follows: a. ΔS° is negative b. ΔS° is negative c. ΔS° is positive d. ΔS° is positive

Step by step solution

01

Analyze Reaction (a)

Reaction (a): K(s) + 1/2 Br2(g) → KBr(s) The reaction involves a solid reactant and a gaseous reactant forming a solid product. There is no increase in the number of moles of gas, as the product is a solid. Therefore, the entropy of the system is expected to decrease.
02

Predict the Sign of ΔS° for Reaction (a)

ΔS° for Reaction (a) is expected to be negative, as the entropy has decreased.
03

Analyze Reaction (b)

Reaction (b): N2(g) + 3 H2(g) → 2 NH3(g) In this reaction, there are 4 moles of gaseous reactants forming 2 moles of gaseous products. The number of moles of gas decreases, so the entropy of the system will decrease.
04

Predict the Sign of ΔS° for Reaction (b)

ΔS° for Reaction (b) is expected to be negative, as the entropy has decreased.
05

Analyze Reaction (c)

Reaction (c): KBr(s) → K+(aq) + Br-(aq) A solid reactant is dissolving into two aqueous ions. Dissolution usually results in an increase in entropy, as the dissolved particles have more freedom to move around in the solution compared to being in a rigid solid state.
06

Predict the Sign of ΔS° for Reaction (c)

ΔS° for Reaction (c) is expected to be positive, as the entropy has increased.
07

Analyze Reaction (d)

Reaction (d): KBr(s) → KBr(l) Here, a solid is changing its state to a liquid. The liquid state has more freedom of motion compared to the solid state, hence, the entropy will increase.
08

Predict the Sign of ΔS° for Reaction (d)

ΔS° for Reaction (d) is expected to be positive, as the entropy has increased. In summary: a. ΔS° is negative b. ΔS° is negative c. ΔS° is positive d. ΔS° is positive

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Most popular questions from this chapter

Consider two reactions for the production of ethanol: $\mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l)$ $\mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l)+\mathrm{H}_{2}(g)$ Which would be the more thermodynamically feasible at standard conditions? Why?

For rubidium \(\Delta H_{\mathrm{vap}}^{\circ}=69.0 \mathrm{kJ} / \mathrm{mol}\) \(686^{\circ} \mathrm{C},\) its boiling point. Calculate $\Delta S^{\circ}, q, w,\( and \)\Delta E$ for the vaporization of 1.00 mole of rubidium at \(686^{\circ} \mathrm{C}\) and 1.00 atm pressure.

Carbon tetrachloride \(\left(\mathrm{CCl}_{4}\right)\) and benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) form ideal solutions. Consider an equimolar solution of \(\mathrm{CC}_{4}\) and \(\mathrm{C}_{6} \mathrm{H}_{6}\) at \(25^{\circ} \mathrm{C}\) . The vapor above the solution is collected and condensed. Using the following data, determine the composition in mole fraction of the condensed vapor.

If wet silver carbonate is dried in a stream of hot air, the air must have a certain concentration level of carbon dioxide to prevent silver carbonate from decomposing by the reaction $$\mathrm{Ag}_{2} \mathrm{CO}_{3}(s) \rightleftharpoons \mathrm{Ag}_{2} \mathrm{O}(s)+\mathrm{CO}_{2}(g)$$ \(\Delta H^{\circ}\) for this reaction is 79.14 \(\mathrm{kJ} / \mathrm{mol}\) in the temperature range of 25 to \(125^{\circ} \mathrm{C}\) . Given that the partial pressure of carbon dioxide in equilibrium with pure solid silver carbonate is $6.23 \times 10^{-3}\( torr at \)25^{\circ} \mathrm{C},$ calculate the partial pressure of \(\mathrm{CO}_{2}\) necessary to prevent decomposition of $\mathrm{Ag}_{2} \mathrm{CO}_{3}\( at \)110 .^{\circ} \mathrm{C}$ (Hint: Manipulate the equation in Exercise 85.)

Predict the sign of \(\Delta S^{\circ}\) and then calculate \(\Delta S^{\circ}\) for each of the following reactions. a. $\mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)$ b. $2 \mathrm{CH}_{3} \mathrm{OH}(g)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)$ c. \(\mathrm{HCl}(g) \longrightarrow \mathrm{H}^{+}(a q)+\mathrm{Cl}^{-}(a q)\)
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