Gen Chem 113- Chapter 15
Mathematically entropy is defined by the equation S = k ln W. W represents the number of possible arrangements, where mathematically W = X^N.X represents the number of (a)____ containing N (b)____.
(a) Cells (b) Molecules
I2 (s) has a very low solubility in H2O (l) because (a)____ forces between I2 and H2O are not strong enough to replace the (b)____ between the H20 molecules.
(a) Dipole-dipole (b) Hydration bonds
In order to assess the spontaneity of a chemical reaction or physical reaction both the charge in (a)______ and (b)_____ associated with the reaction or process must be known.
(a) Enthalpy (b) Entropy
The second law of thermodynamic state that the total (a)____ of the universe will (b)____ for any spontaneous process.
(a) Entropy (b) Increase
A solution forms when the attractive (a)____ between the solute and the solvent are similar in (b)____ to the solvent-solvent and solute-solute attractions and therefore able to replace them.
(a) Forces (b) Magnitude
The Gibbs (a)_____ energy change (symbolized by Δ (b)____) is a measure of the spontaneity of a process, and of the useful energy available from it.
(a) Free (b) G
A solution has a (a)____ entropy than either the pure solvent or pure solute because in the solution there are a (b)____ number of interactions between particles and therefore (c)____ ways to. distribute. the energy of the system.
(a) Higher (b) Greater (c) more
The dissolution of a molecular solute typically results in a(n) (a)____ in entropy because the system's molecules and (b)____ are dispersed into a larger volume. (Assume that the solute is not an acid or base.)
(a) Increase (b) Energy
If a given reversible reaction has positive values for both ΔH and ΔS, the value of ΔG will become (a)_____ negative as temperature increases and the formation of the (b)_____ will be increasingly favored.
(a) More (b) Products
When the Gibbs free-energy change for a reaction is less than zero (negative), that reaction is (a)____ and the entropy change (Delta S) for the universe is (b)____.
(a) Spontaneous (b) Positive
The Delta G for a. reaction that occurs under standard-state condition is called (a)____ Gibbs free energy of reaction. The term "standard state" implies a temperature of (b)____°C or (c)____K for the. reaction.
(a) Standard (b) 25 (c) 298.15
In order to determine the spontaneity of a reaction or process, the entropy changes in both the (a)____ and the (b)____ must be considered.
(a) System (b) Surroundings
The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is 0. This allows for the calculation of (a)____ entropies unlike standard (b)____ of formation, which derived using arbitrary reference.
(a) absolute (b) enthalpies
Since entropy is typically tabulated in units of (a)____/K and standard enthalpies are typically tabulated in units of (b)____/mol, it is usually necessary to perform a unit conversion when calculating Gibbs free energy.
(a)J (b) kJ
Which of the following compounds are expected. to be soluble in carbon tetrachloride (CCl4) based on the structure? (a) NaCl (b) H2O (c) C6H6 (d) CO2
(c) C6H6 (d) CO2
Which of the following processes or changes will lead to a decrease in entropy? (a) melting (b) a reaction resulting in the formation of a greater number of. gas molecules (c) temperature decrease (d) condensation
(c) Temperature decrease (d) Condensation
A reaction taking place at 100°C has an entropy change of 200 J/K and an enthalpy change of -20 kJ. What expression would be used to calculate Delta G under these condition?
-20,000-(373)(200)
What familiar processes is/are spontaneous?
A ball rolling downhill. A teaspoon of table salt dissolving in 1 L of boiling water.
What is an application of the second law of thermodynamics?
A gas expands because matter tends to spread out.
Entropy will generally increase when ____.
A liquid evaporates A solid sublimes A molecular substance dissolves in water
What is the relationship between spontaneity of a reaction and the sign of Delta H?
A negative value of Delta . - A negative value of Delta H favors spontaneity, but. does not assure it. The sign of Delta H alone is not sufficient evidence to determine the spontaneity of if a process.
Describe the relationship between the entropy and the spontaneity of a process.
A reaction/ process in which Delta S sys > 0 and Delta S surr > 0 will be. spontaneous.
Which of the following statements regarding spontaneous processes is not true? A. Spontaneous processes are exothermic. B. Spontaneous processes proceed without outside intervention once initiated. C. Spontaneous reactions are not always rapid. D. The motional freedom of particles tends to increase during spontaneous change. E. Particles tend to become more spread out during spontaneous change.
A. Spontaneous processes are exothermic.
Which of the following best describes the change in free energy for a reaction at equilibrium? A. ΔG = 0 B. ΔG > 0 C. ΔG < 0 D. ΔG < ΔH + TΔS E. ΔG > ΔH + TΔS
A. ΔG = 0
The importance of the third law of thermodynamics is that it allows to experimentally determine ____.
Absolute entopies
What changes are favored in a spontaneous process?
An overall decrease in energy An increase in entropy
What is favored in a spontaneous process?
An overall decrease in energy An increase in entropy
Miscible liquids are liquids that ____.
Are soluble in each other in all proportions.
How many possible microstates exist in a perfect, crystalline solid at absolute zero (0 K)? A. 0 B. 1 C. 2 D. 3 E. 4
B. 1
The reverse of the reaction below is always spontaneous but proceeds slower at low temperatures than at high temperatures. Which of the following conclusions is correct about the reaction below in the forward direction? A ----> B A. The reaction is spontaneous at high temperatures. B. The reaction is endothermic and never spontaneous. C. The reaction is exothermic and never spontaneous. D. The reaction is nonspontaneous at low temperatures. E. The reaction is endothermic and always spontaneous.
B. The reaction is endothermic and never spontaneous.
Consider a. glass of ice water at its melting point, 0°C. Which of the following is true at this temperature? A. All of. the water will spontaneously freeze. while the ice will spontaneously melt. B. The system is at equilibrium and will not freeze nor melt spontaneously. C. The ice will spontaneously melt until the entire sample is liquid water. D. ΔG > 0 for the melting of ice to liquid water E. The system will proceed in the direction that produces an equal ratio of water and ice and then stop changing.
B. The system is at equilibrium and will not freeze nor melt spontaneously.
Which of the following is always true for a spontaneous exothermic process? A. ΔS sys < 0 B. ΔS surr > 0 C. ΔS universe = 0 D. ΔS sys > 0 E. ΔS surr < 0
B. ΔS surr > 0
During which of the following processes is ΔS°sys< 0? A. Salt crystals dissolve in water. B. Air escapes from a hole in a balloon. C. Elemental iron and oxygen react to form rust (Fe2O3). D. Ice melts in your hand. E. Water boils in a pan.
C. Elemental iron and oxygen react to form rust (Fe2O3).
Which of the following correctly describes the concept. of free energy? A. Free energy is. the energy obtained by a reaction at no cost. B. When a reaction is exothermic, energy is released and the reaction is always spontaneous. C. Free energy is the energy that is made available to do useful work in a reaction. D. When a reaction increases in entropy, energy is released, and the reaction is always spontaneous. E. Reactions always proceed spontaneously in the direction that increases free energy.
C. Free energy is the energy that is made available to do useful work in a reaction.
The _____ Law of Thermodynamics states that the entropy change in an isolated system during a spontaneous process must be greater than zero: A. Zeroth B. First C. Second D. Third E. None is correct.
C. Second
Define the third law of thermodynamics. A. The energy in a system is dispersed by increasing the entropy and decreasing the enthalpy of the system. B. Energy cannot be created nor destroyed in an isolated system. C. The entropy of a system approaches zero as the temperature approaches absolute zero. D. Entropy is proportional to the number of possible microstates a system may adopt. E. The entropy change of the universe in a spontaneous process is greater than zero.
C. The entropy of a system approaches zero as the temperature approaches absolute zero.
What must be known in. order to assess the spontaneity of a chemical reaction or physical process at a particular set of conditions?
Change in entropy Change in enthalpy
Consider the process of ammonia vapor condensing in to liquid ammonia. Under what conditions is the process spontaneous? A. The process is spontaneous under all conditions. B. The process is never spontaneous under any conditions C. The process is spontaneous at high temperatures. D. The process is spontaneous at low temperatures. E. There is not enough information given to predict the spontaneity of this process.
D. The process is spontaneous at low temperatures.
What is sign indicates whether a reaction or process will occur spontaneously?
Delta G
Math the value of Gibbs free-energy change for a reaction with its implication. (a) Delta G < 0 (b) Delta G > 0 (c) Delta G = 0 1. Non-spontaneous process 2. Spontaneous process 3. Process at equilibrium
Delta G < 0 ----> Spontaneous process Delta G > 0 ----> Non-spontaneous process Delta G = 0 ----> Process at equilibrium
What is the correct form of change in Gibbs. equation for a process occurring at constant temperature?
Delta G sys = Delta H sys - T*Delta S sys
Math each thermodynamic quantity with the information it provides about a given reaction. (a) Delta G° < 0 (b) Delta G° > 0 (c) Delta G < 0 (d) Delta g > 0 1. Products are favored at equilibrium. 2. Reactions will be non-spontaneous. 3. Reaction will occur spontaneously. 4. Reactants are favored at equilibrium.
Delta G° < 0 ----> Products are favored at equilibrium. Delta G° > 0 ----> Reactants are favored at equilibrium. Delta G < 0 ----> Reaction will occur spontaneously. Delta g > 0 ----> Reactions will be non-spontaneous.
Match the sign Delta G with the direction of reaction that is favored for a system at equilibrium. (a) Delta G° > 0 (b) Delta G° < 0 1. Favors reactants 2. Favors products
Delta G° > 0 ----> Favors reactants Delta G° < 0 ----> Favors products
Describe the standard free-energy of formation (Delta G°f) for a substance.
Delta G°f for any element in its most stable form at 1 atm is equal to zero. Delta G°f is the free energy change for the synthesis of 1 mole of a compound from its constituent elements in their standard states.
When heat, q, is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. What equation reflects this relationship (a a constant pressure)?
Delta S surr = - Delta H sys/T Delta S surr = - q sys/T
At a certain temperature, the change in entropy of the system is calculated to be Delta S sys. If the system is at equilibrium, what is the value of Delta S surr under these conditions?
Delta S surr = - Delta S sys
A particular process results in a decrease in entropy of the system. If this process is spontaneous, what must be true. about the entropy change of the surroundings?
Delta S surr > - Delta S sys
What values must be known in order to calculate the change in Gibbs free energy using the Gibbs equation.
Delta S sys T Delta H sys
A reaction is found to be spontaneous only at high temperatures. What has to be true?
Delta S° rxn > 0 Delta H° rxn > 0
What are the signs of ΔS, ΔH, and ΔG for the condensation of water on the sides of a glass of ice tea at room temperature? A. +, +, - B. -, +, - C. +, -, - D. -, +, + E. -, -, -
E. -, -, -
Which of the following statements is false? A. The combustion of methane gas is spontaneous because once it is ignited it continues to burn on its own. B. Iron turns into rust without external intervention, which means that this reaction is spontaneous. C. Not all exothermic reactions are spontaneous, and some endothermic reactions are spontaneous under certain reaction conditions. D. In a spontaneous reaction, the particles of the system and the surroundings combined are more spread out and have more freedom of motion overall after the reaction happens than before. E. All spontaneous reactions occur faster than non-spontaneous reactions.
E. All spontaneous reactions occur faster than non-spontaneous reactions.
The ____ of a system is a measure of the ways in which the energy of the system can. be dispersed.
Entropy
The measure of the degree of dispersion of the energy of a system us called ____.
Entropy
What quantity is a measure of how spread out or dispersed a system's energy is?
Entropy
A system is in a sate of ____ when Delta S univ = 0
Equilibrium
Ethanol and water are miscible. What does this mean?
Ethanol and water. are. soluble in each other in all proportions.
What is the general trends in standard entropy?
Fore 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.
What conditions are specified by standard-state conditions?
Gases are 1 atm pressure The standard state of an element is its allotropic form at standard-state temperature and pressure. A solution will have a concentration of 1 M.
The entropy of gaseous molecules is ____ the entropy of these molecules in a condensed phase. Therefore, reactions producing a greater number of gas molecules typically result in a positive change in entropy.
Greater than
In each of the following pairs, which species will have a greater value for standard entropy? (i) F(g) vs. H2OG(g) (ii) H2O2 (l) vs. H2O2 (g)
H2O (g) H2O2 (g)
____ is the process of stabilizing the particles of an ionic solute in aqueous solution by surrounding them with water molecules, which form ion-dipole interaction.
Hydration
What is the relationship between Delta S surr, Delta H sys, and T?
If Delta H sys is positive, Delta SS surr will be positive. Delta S surr is inversely proportional to temperature.
The combustion reaction of glucose is exothermic. C6H12O6 (s) + 6O2 (g) --> 6CO2 (g) + 6H2O (g) Does this reaction cause an increase or decrease in entropy of the systems surrondings?
Increase in the entropy of the surroundings Increase in the entropy of the system
Which. of the following familiar process is/are spontaneous. under the conditions stated?
Irons rusting at room temperature Ice melting at room temperature
In order for the products to be favored in a reaction, the standard free-energy change (Delta G degree) must have a ____ sign.
Negative
Match each symbol in the equation S = k ln W correctly with its definition. (a) entropy (b) natural logarithm (c) number of possible arrangements (d) Boltzmann constant
S <---> Entropy k <---> Boltzmann constant ln <---> Natural Logarithm W <---> Number of possible arrangements
What is the entropy of a system in which there is only one microstate?
S = ln k
Match each definition with the appropriate term. Spontaneous Process Non-spontaneous Process (a) A process that does occur under a given set of conditions (b) A process that does not. occur under a given set of conditions
SP <----> A process that does occur under a given set of conditions NP <--->A process that does not. occur under a given set of conditions
Two unknown reactions (A and B) are analyzed. It is. found that reaction A is exothermic, while reaction B is endothermic. Which of these reactions is spontaneous?
Spontaneity cannot be determined from the. given information. -We must also know how the entropy of the system changes to assess spontaneity. Spontaneity is determined by the sign Delta G and is a function of both Delta H, and Delta G is a function of both Delta H and T Delta S.
The ____ entropy of a substance is its absolute entropy at 1 atm.
Standard
Gibbs free energy is used most prevalently to determine the spontaneity of a reaction because it is only dependent on the ____, making it much more convenient to measure experimentally.
System
What information is needed in order to calculate the temperature at which a reaction changes from being non-spontaneous to spontaneous if Delta H = 171 kJ/mol and Delta S = 161 J/K*mol.
T = Delta H/Delta S T = 171 kJ/mol / o.161 kJ/mol*K Set Delta G = 0
Will HCl (g) or NaCl (s) be more soluble in the solvent CH3OCH3?
The dipole-dipole forces in an HCl/CH3OCH3 solution are. similar in strength to. the dipole-dipole forces between CH3OCH3 molecules. HCl (g) will. be more soluble in CH3OCH3.
A reaction that results in an overall increase in the number of gas molecules has a positive sign. for DeltaS rxn. Why?
The entropy of a substance in a gas phase is much higher than its entropy in the liquid or solid phase.
An atom of hydrogen is bound to a metal surface (but free to move across it) with 10 possible sites of attachment. What would be. the effect of. increasing the size of the metal surface to 20 possible sites?
The entropy would increase, but it would be less than double the original entropy.
AN atom of hydrogen is bound to a metal surface (but free to move across it) with 10 possible sites of attachment. What would be the effect of increasing the size of the metal surface to 20 possible sites?
The entropy would increase, but it would be less than double. the original entropy.
Describe the behavior of a reversible reaction for which both Delta. H and Delta S < 0.
The formation of the reactants will become increasingly favored as the temperature rises. At low temperatures, Delta G rxn < 0. The reaction will become less spontaneous as the temperature increases.
The equation DeltaS sys= NR ln V final/V initial is much more frequently used than the Boltzmann equation DeltaS sys = k ln W final/W initial because ____.
The number of mircrostates is difficult to determine for the a real process.
Describe what happens when increase in entropy occurs when substance changes from solid to liquid, or liquid to gas.
The number of possible arrangements of particles increase. The energy of the particles increase during these phase changes.
Describe the change in entropy when a solution is formed.
The particles in a solution. generally have greater freedom of movement than. the particles in a pure solute. Entropy usually increases when a solution forms because there are more interactions between particles in a solution.
Thermodynamics tells us nothing about the ____ of a reaction.
The rate
Match the prediction of the spontaneity of a given process with a combination of Delta H and Delta S values. (a) The reaction is always spontaneous if (b) The reaction is always non-spontaneous if (c) The reaction is spontaneous only at low T if (d) The reaction is spontaneous only at high T if 1. Delta H > 0 and Delta S > 0 2. Delta H < 0 and Delta S < 0 3. Delta H < 0 and Delta S > 0 4. Delta H > 0 and Delta S < 0
The reaction is always spontaneous if ----> Delta H < 0 and Delta S > 0 The reaction is always non-spontaneous if ----> Delta H > 0 and Delta S < 0 The reaction is spontaneous only at low T if ----> Delta H < 0 and Delta S < 0 The reaction is spontaneous only at high T if ----> Delta H > 0 and Delta S > 0
What effect does increasing the temperature of a gas have on its entropy?
There is an increase. in the entropy of the system as temperature increases. The kinetic energy of. the particles in the system increase.
Match the different forms of motional energy of molecules with their descriptions. Translational Vibrational Rotational (a) Atoms in the molecule move. relative to one another. (b) Atoms spin about an axis running through the center of mass of the molecule (c) The entire molecule moves through space.
Translational <---> The entire molecule moves through space. Vibrational <---> Atoms in the molecule move. relative to one another. Rotational <---> Atoms spin about an axis running through the center of mass of the molecule.
True or False: Entropy measures how dispersed the energy if a system is.
True
True or false: A reaction with a positive Delta S univ may occur quickly or slowly.
True
True or false: If a process occurs in one direction under a certain set of conditions, it does not occur spontaneously in the opposite direction under the same conditions.
True - If a process occurs spontaneously in one direction under a certain set of conditions, it is not possible for the process to also occur spontaneously in the opposite direction under the same set of conditions.
True or false: The state with the largest number of possible arrangements has the greatest entropy.
True - The most probable state is one with the largest number of energetically equivalent possible arrangements: S = k ln W.
What energies are forms of motional energy?
Vibrational Translational Rotational
Four particles initially in one flask are allowed to. also expand into a second flask. What are the value(s) for the number of microstates (W) and change in. entropy of. the system. Recall. that W=Xn where X is the number of cells and N is the number of particles.
W final = 2^4 = 16 microstates Delta S sys = k ln 2^4
Correctly describe the mircostates of a system, W.
W is the number of energetically equivalent ways the particles of a system may be arranged. Increasing the temperature of a system will increase W. Entropy increase with the number of microtates.
Describe the changes. that occur when an ionic solid dissolves in water.
When highly charged ions dissolves, the entropy of the system decreases. The dissolution of ions with low changes typically result in an increase in the entropy of the system. The mobility if the H2O molecules in such a solution is reduced they are arranged in a specific way that the dissolved ions.
Match the symbols n, R, V final, and V initial to the definition. (a) number of moles (b) final volume (c) initial volume (d) ideal gas constant
n <----> Number of moles R <----> Ideal gas constant V final <----> Final volume V initial <----> Initial volume