4. At 25° C, the enthalpy change AH° for the ionization of an acid HA is +6.3 kJ/mol, and the entropychange AS° is +0.0048 kJ/(mol K). What is the pka of this acid?

Given Temperature ( T ) = 25 ℃ = (25 + 273 )K…

Answered: 4. At 25° C, the enthalpy change AH°…

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Chapter17: Spontaneity, Entropy, And Free Energy

Section: Chapter Questions

Problem 20Q: The deciding factor on why HF is a weak acid and not a strong acid like the other hydrogen halides...

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10.46 Discuss the effect of temperature change on the spontaneity of the following reactions at 1 atm. (a) Al2O3(s)+2Fe(s)2Al(s)+Fe2O3(s) H = 851.5kJ; S =38.5 J/K (b) N2H4(l)N2(g)+2H2(g) H =-50.6 kJ; S= 0.3315 kJ/K (c) SO3(g)SO2(g)+12O2(g) H = 98.9 kJ; S= 0.0939 kJ/K
On the basis of your experience, predict which of the following reactions are spontaneous. (a) CO2(s)CO2(g) at 25°C (b) NaCl(s)NaCl(l) at 25°C (c) 2NaCl(s)2Na(s)+Cl2(g) (d) CO2(g)C(s)+O2(g)
Consider two processes: sublimation of I2(s) and melting of I2(s) (Note: the latter process can occur at the same temperature but somewhat higher pressure). I2(s)I2(g)I2(s)I2(l) Is S positive or negative in these processes? In which of the processes will the magnitude of the entropy change be greater?
What types of experiments can be carried out to determine whether a reaction is spontaneous? Does spontaneity have any relationship to the final equilibrium position of a reaction? Explain.
Given that H f for HF(aq) is -320.1 kJ/mol and S for HF(aq) is 88.7 J/mol K, find Ka for HF at 25C.
The free energy change, G, for a process at constant temperature and pressure is related to Suniv and reflects the spontaneity of the process. How is G related to Suniv? When is a process spontaneous? Nonspontaneous? At equilibrium? G is a composite term composed of H, T, and S. What is the G equation? Give the four possible sign combinations for H and S. What temperatures are required for each sign combination to yield a spontaneous process? If G is positive, what does it say about the reverse process? How does the G = H TS equation reduce when at the melting-point temperature of a solid-to-liquid phase change or at the boiling-point temperature of a liquid-to-gas phase change? What is the sign of G for the solid-to-liquid phase change at temperatures above the freezing point? What is the sign of G for the liquid-to-gas phase change at temperatures below the boiling point?
Estimate the temperature range over which each of the following reactions is spontaneous. (a) 2Al(s)+3Cl2(g)2AlCl3(s) (b) 2NOCl(g)2NO(g)+Cl2(g) (c) 4NO(g)+6H2O(g)4NH3(g)+5O2(g) (d) 2PH3(g)3H2(g)+2P(g)
The deciding factor on why HF is a weak acid and not a strong acid like the other hydrogen halides is entropy. What occurs when HF dissociates in water as compared to the other hydrogen halides?
When ammonium chloride is added to water and stirred, it dissolves spontaneously and the resulting solution feels cold. Without doing any calculations, deduce the signs of G, H, and S for this process, and justify your choices.
Show by calculation, using Appendix 1, whether dissolving lead(II) chloride PbCl2(s)Pb2+(aq)+2Cl(aq) is spontaneous at 25C (a) when [ Pb2+ ]=1.0M;[ Cl ]=2.0M. (b) when [ Pb2+ ]=1.0105M;[ Cl ]=2.0105M.
Some metal oxides, such as lead(II) oxide, can be decomposed to the metal and oxygen simply by heating. PbO(s)Pb(s)+12O2(g) (a) Is the decomposition of lead(II) oxide product-favoredat 25 C? Explain. (b) If not, can it become so if the temperature is raised? (c) As the temperature increases, at what temperature doesthe reaction first become product-favored?

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4. At 25° C, the enthalpy change AH° for the ionization of an acid HA is +6.3 kJ/mol, and the entropy change AS° is +0.0048 kJ/(mol K). What is the pKa of this acid?