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Exam 19: Thermodynamics

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Question 31

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For a chemical reaction, ΔH° = +21.16 kJ mol⁻¹. The value of ΔS° for the same reaction was +74.50 J mol⁻¹ K⁻¹. If, since the physical states do not change, the value of ΔH^° and ΔS° do not change with temperature over the range of interest, what should be the value of ΔG°_T at+550.0 °C?

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Question 32

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Which species has the highest standard entropy (S°) for one mole of substance?

A) Au(s)
B) Cd(s)
C) Hg(l)
D) Ni(s)
E) K(s)

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Question 33

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Using the data: C₂H₄(g) , $\Delta$ H°_f = +51.9 kJ mol^-1, S° = 219.8 J mol^-1 K^-1 CO₂(g) , $\Delta$ H°_f = -394 kJ mol^-1, S° = 213.6 J mol⁺¹ K^-1 H₂O(l) , $\Delta$ H°_f = -286.0 kJ mol^-1, S° = 69.96 J mol^-1 K^-1 O₂(g) , $\Delta$ H°_f = 0.00 kJ mol^-1, S° = 205 J mol^-1 K^-1 Calculate the maximum amount of work that can be obtained, at 25.0 °C, from the process:C₂H₄(g) + 3 O₂(g) $\rarr$ 2 CO₂(g) + 2 H₂O(l)

Which set below has the species listed in order of increasing standard entropy, S°?

A negative value for the standard molar entropy, S°, of a chemical substance indicates that the substance is unstable and may decompose or detonate if mishandled.

Consider a reaction that is both endothermic and increasingly ordered. How will temperature affect the spontaneity of the process?

For the system, 2 NO₂(g) N₂O₄(g), ΔG° = −5.40 kJ. Calculate the value of the equilibrium constant, K_p, for this system.

Which of the following is the best example of a thermodynamically reversible process?

For the reaction H₂(g)+ S(s)→ H₂S(g), ΔH° = -20.2 kJ/mol and ΔS° = +43.1 J/K·mol, at which temperatures would the reaction be spontaneous?

Which set has the species listed in order of increasing standard entropy, S°?

Consider a reaction that is both endothermic and increases entropy. How will temperature affect the spontaneity of the process?

Which species has the greatest standard entropy (S°) for one mole of substance?

Using the data, I₂(g), ΔH°_f = +62.4 kJ mol⁻¹, S° = +260.7 J mol⁻¹ K⁻¹ I₂(s), ΔH°_f = 0.00 kJ mol⁻¹, S° = +116.12 J mol⁻¹ K⁻¹ calculate the temperature at which solid iodine should have a vapor pressure of 1.00 atm, based on the reaction, I₂(g) I₂(s).

The normal melting point of benzoic acid is 122.4°C. Predict the signs of $\Delta$ H, $\Delta$ S, and ?G for the process in which liquid benzoic acid freezes at 120°C and 1 atm: C₇H₆O₂(l) .C₇H₆O₂(s)

Which process is accompanied by an increase in the entropy of the system?

The standard entropy, S° for an element in its standard state is always zero.

Describe, using the free energy relationship ΔG = ΔH - TΔS, the process of a hot object coming into thermal equilibrium with a cold object.

Three factors which, acting together, determine whether a reaction is spontaneous or not, are entropy, internal energy, and enthalpy.

The equilibrium constant at 25°C for the reaction 2NO(g) + O₂(g) 2NO₂(g) is K_p = 1.65 × 10¹². Calculate the value of $\Delta$ G° for the reaction at this temperature.

The normal freezing point of ammonia is -78°C. Predict the signs of ΔH, ΔS, and ΔG for ammonia when it melts at -76°C and 1 atm: NH₃(s)→ NH₃(l)