General Chemistry II: Chapter 18: Thermodynamics
Calculate the entropy change of the surroundings in J/mol∙K when 30 kJ of heat is released by the system at 27° C.
+100
Match the values of ∆G° with associated equilibrium constants. (Note that all ∆G° values are rounded to 1 significant figure.) ∆G° = 0 ∆G° = +100 kJ ∆G° = -100 kJ ∆G° = -10 kJ
K =1 K = 3 x 10⁻¹⁸ K = 3 x 10⁻¹⁷ K = 5 x 10¹
When a reaction is at equilibrium, the reaction quotient Q is always equal to ______ and ∆G is equal to ________.
K, 0
Under what conditions will the reaction of graphite shown below be spontaneous? C (s) + 2Cl₂ (g) →CCl₄ (g); ∆H° = -106.7kJ
Spontaneous only at low T
A reaction that results in an overall increase in the number of gas molecules has a positive sign for ∆S rxn. Select the statement that correctly explains why.
The entropy of a substance in a gas phase is much higher than its entropy in the liquid or solid phase.
True or false: A reaction with a positive ∆S univ may occur quickly or slowly.
True
For a chemical reaction,ΔS°rxn = ΣnS°(____________) - ΣnS°(_________).
products reactants
The _____entropy of a substance is its absolute entropy at 1 atm.
standard
Match the relative values of Q and K with the associated value of ∆G. Q < K Q > K Q = K
∆G < 0 ∆G > 0 ∆G = 0
Which of the following options correctly describe the free-energy change and spontaneity of the reaction Cu₂O (s) →Cu (s) + 1/2 O₂ (g) at 375 K if ∆H = 168 kJ/mol and ∆S = -9.63 J/K∙mol? Select all that apply.
∆G = +172 kJ The reaction is not spontaneous at this temperature.
Which of the following options correctly describe the free-energy change and spontaneity of the reaction Cu₂O (s) → Cu (s) + 1/2 O₂ (g) at 375 K if ∆H = 168 kJ/mol and ∆S= -9.63 J/K∙mol? Select all that apply.
∆G = +172 kJ The reaction is not spontaneous at this temperature.
Consider a hypothetical reaction in which compound 1 → compound 2. Match each letter from the energy diagram with its associated meaning. A B C D
∆G° (compound 1) ∆G° (compound 2) ∆G° rxn Point of equilibrium
Ksp for iron (lll) hydroxide [Fe(OH₃] is equal to 1.1 x 10⁻³⁶ at 25°C. Determine ∆G° (in KJ/mol) at 25°C for the reaction represented by the equation Fe(OH)₃ (s)⇌ Fe³⁺ (aq) + 3OH⁻ (aq).
+205 kJ/mol
Calculate the standard entropy change for the following reaction at 25° C. Use the values provided in the table below. 2CO (g) + O₂ → 2CO₂ (g)
-173.6 J/mol∙K
Which of the following statements correctly reflect the relationship between the spontaneity of a reaction and the sign of ∆H? Select all that apply.
-An endothermic process may be spontaneous under one set of conditions but nonspontaneous at a different temperature and pressure. -It is possible for an exothermic process to be nonspontaneous.
The equilibrium constant for the reaction shown below is 7 x 10⁻⁸⁴. What information does this provide about the reaction? Select all that apply. H₂ (g) + I₂ (g) ⇌ 2HI (g)
-At equilibrium the reaction mixture consists mostly of H₂ (g) and I₂ (g) -∆G° positive for this reaction
Which of the following options correctly explain the impact of ∆H sys on the entropy change of the surroundings? Select all that apply.
-At high temperature, the enthalpy change of the system will have a relatively small effect on the entropy of the surroundings. -The lower the temperature, the greater the effect of ∆H sys on the entropy of the surroundings.
Which of the following statements correctly describe the general trends in standard entropy? Select all that apply.
-For two monatomic species, the one with the larger molar mass will have a higher standard entropy. -For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy.
Which of the following options correctly reflect the relationships between ∆S surr, ∆H sys, and T (at constant pressure so q sys =∆H sys)? Select all that apply.
-If ∆H sys is negative, ∆S surr will be positive -∆S surr is inversely proportional to temperature.
Which of the following process are spontaneous under the conditions stated? Select all that apply.
-Iron using at room temperature when exposed to water and oxygen -Ice melting at room temperature
Which of the following options correctly explain why the equation S = k in W is rarely used to calculate the change in entropy of a system? How is ∆S determined? Select all that apply.
-It is difficult to determine the number of possible microstates (W) for a macroscopic system. -Entropy can be measured using calorimetric methods. -Tabulated standard entropy values are used to calculate entropy changes.
Spontaneous process Nonspontaneous process
-Occurs under specified conditions without a continuous input of energy -Requires a continuous input of energy under specified conditions
Match each state of matter with the appropriate characteristics at standard state. Gases Solutions Solids or liquids
-Pressure of 1 atm -1 M concentration -Pure substance in its most stable form
Match the sign of ∆G° with the direction of reaction that is favored for a system at equilibrium. ∆G° > 0 ∆G° < 0
-Reactants are favored at equilibrium -Products are favored at equlilbrium
What statements correctly describe the entropy changes that occur when an ionic solid dissolves in water? Select all that apply.-
-The dissociation of an ionic solute in water causes the entropy of the system to increase. -The hydration of highly charged ions generally results in a decrease in the entropy of the system. -The mobility of H₂O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions.
What effect does increasing the temperature of a gas have on its entropy, and why? Select all that apply.
-The entropy of a system increases as the temperature increases. -As the temperature of a system is increased, all types of kinetic energies increase.
Which of the following options correctly describe the Gibbs free-energy (∆G) of a system? Select all that apply.
-The free-energy change for a process is a measure of the useful work it can provide. -∆G is a measure of the spontaneity of a process.
Which of the following statements correctly explain the increase in entropy that occurs when a substance changes from a solid to a liquid, or from a liquid to a gas? Select all that apply.
-The freedom of movement of the particles increases in the change solid → liquid →gas. -The energy of the particles increases during these phase changes.
Which of the following statements correctly describe the standard free energy of formation (∆G°f) for a substance? Select all that apply.
-∆G°f is the free-energy change for the synthesis of 1 mole of a compound from its constituent elements in their standard states. -∆G°f for any element in its most stable allotropic form at 1 atm is equal to zero.
The standard free-energy change for a reaction is the free-energy change for the reaction under standard-state conditions, which assumes that all gases are at ______ atm of pressure and all solutions have a concentration of ______ M.
1, 1
A chemist finds that the sublimation of a compound has a free-energy change of -2.5 kJ at 350°C, and a free-energy change of +0.5 kJ at 140°C. From this information, what is a likely value for the temperature of sublimation?
175°C
Which equation would be used to calculate ∆G° rxn for the reaction 2A + B→3C +D?
3(40) - 20-2(10) + 5
What is a spontaneous process?
A process that occurs under specified conditions without a continuous input of energy.
In which cases do the substance(s) on the left have a higher entropy than the substance(s) on the right? Select all that apply.
C₃H₈ (g) vs. C₂H₆ (g) 2NO₂ (g) vs. N₂O₄ (g)
Which of the following correctly describes the first law of thermodynamics?
Energy can be converted from one form to another, but it cannot be created or destroyed.
Match each symbol in the equation S=k in W correctly with its meaning. S k W ln
Entropy Boltzmann constant Number of microstates Natural logarithm
H₂O (l) → H₂O (s); ∆S sys = -22 J/K Which of the following is the best explanation for the way in which this process obeys the second law of thermodynamics?
Freezing is exothermic: the surrounding increase in entropy.
Which of the following reactions are predicted to have a positive value for ∆S rxn? Select all that apply.
H₂CO₃ (aq) → H₂O (l) ₊ CO₂ (g) N₂O₄ (g) → 2NO₂ (g)
Since entropy is typically tabulated in units of ______ / K and standard enthalpies are typically tabulated in units of _____/ mol, it is usually necessary to perform a unit conversion when calculation Gibbs free energy.
J, kJ
Match the values of ∆G° with associated equilibrium constants. (Note that all ∆G° values are rounded to 1 significant figure.) ∆G°= 0 ∆G°= +100 kJ ∆G°= -100 kJ ∆G°= -10 kJ
K = 1 K = 3 x 10⁻¹⁰ K = 3 x 10⁻¹⁷ K = 5 x 10¹
Match the value of the Gibbs free energy change for a reaction with its implication. ∆G < 0 ∆G > 0 ∆G = 0
Spontaneous process Nonspontaneous process Process at equilibrium
If the reaction shown below is to be coupled to a second reaction in order to generate an overall spontaneous process, what must be true regarding the second reaction? Fe₂O₃ (s) → 2 Fe (s) + 3/2 O₂ (g); ∆G = 740.98 kJ
The free-energy change must be more negative than -740.98 kJ
The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is 0. This allows for the calculation of _______ entropies unlike standard ______ of formation, which are derived using an arbitrary reference.
absolute enthalpies
The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is 0. This allows for the calculation of ________ entropies unlike standard ________ of formation, which are derived using arbitrary reference.
absolute enthalpies
The value of ∆G⁰ calculated using the equation ∆G⁰ - T∆S⁰ for temperatures other than 298 K is ______.
an estimate, because both ∆H° and ∆S° change with temperature.
Third law of thermodynamics states that a perfect ______ of a pure solid substance has _______ entropy at a temperature of 0 K.
crystal zero
In order to asses the spontaneity of a chemical reaction or physical process both the change in _____ and _____ associated with the reaction or process must be known.
enthalpy and entropy
The _______of a system, symbolized by the letter S, is related to the number of different possible ways the energy of a system can be dispersed.
entropy
The second law of thermodynamics states that the total _____ of the universe will ______ for any spontaneous process.
entropy; increase
A system is in a state of __________ when ∆S univ =0.
equilibrium
As the temperature of a system increases, the entropy____due to a(n) _____ in the number of available energy states and thus a(n) ______ in the number of possible arrangements of molecules within those energy states.
increase; increase; increase
As the number of microstates ______ the entropy of the system_____.
increases, increases
The different possible ways for arranging the particles of a system are called ____. The greater the number of these states, the______ the entropy of the system.
microstates; larger
If a given reversible reaction has positive values for both ∆H and ∆S, the value of ∆G will become _____ negative as temperature increases, and the formation of the _____ will be increasingly favored.
more; products
A process that can occur without a continuous input of energy is a(n) _____ process.
spontaneous
In order to determine the spontaneity of a reaction or process, the entropy changes in both the ________ and ________must be considered in order to evaluate ∆S univ.
system surroundings
Based on the equation ∆G = ∆G° + RT In (Q), match each range of Q values to the correct relationship between the magnitudes of ∆G and ∆G°. (Recall that the sign indicates whether the change is into (positive) or out of (negative) the system. Therefore, focus on the magnitudes of the values for the free energies, not their signs.) Q = 1 Q < 1 Q > 1
∆G = ∆G° ∆G > ∆G° ∆G < ∆G°
The sign of which quantity indicates whether or not a particular reaction or process will occur spontaneously?
∆G° with
Match the prediction of the spontaneity of a given process with the appropriate combination of ∆H and ∆S values. The reaction is always spontaneous if The reaction is always nonspontaneous if The reaction is spontaneous only at low T if The reaction is spontaneously at high T if
∆H < 0 and ∆S > 0. ∆H > 0 and ∆S < 0. ∆H < 0 and ∆S < 0. ∆H > 0 and ∆S > 0.
The reaction 4Fe (s) + 30₂ (g) + 6H₂O (l) → 4Fe(OH)₃ (s) spontaneous at temperature below 1950°C. If ∆H = -1582 kJ, calculate the entropy change for this reaction at 1950°C.
∆S = -712 J/K
Which of the following options correctly show how to calculate the entropy change of a system? Select all that apply.
∆S = Sf -SI ∆S = k in Wf / Wl
When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflected?
∆S surr = - q sys/T ∆S surr = -∆H sys/T
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?
∆S surr > -∆S sys
Which of the conditions described below will result in a spontaneous reaction? Select all that apply.
∆S sys = -20J/K; ∆s surr = 25 J/K ∆S sys = 30 J/K; ∆s surr = 10 J/K
When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflect this relationship (at constant pressure)?
∆Ssurr = -∆H sys/ T
Which of the following is the correct form of the Gibbs equation for a process occurring at constant temperature?
∆Ssys = ∆Hsys -T∆Ssys
