Chemistry 2 Test - Chapter 19

Consider the vaporization of liquid water to steam at a pressure of 1 atm. Is this process endothermic or exothermic?

endothermic

How does the entropy of the system change when equal volumes of ethanol and water are mixed to form a solution?

increases

How does the entropy of the system change when the temperature of the system increases?

increases

How does the entropy of the system change when the volume of a gas increases?

increases

What can be said about an exothermic reaction with a negative entropy change?

spontaneous at low temperatures.

What can be said about an endothermic reaction with a negative entropy change?

spontaneous in the reverse direction at all temperatures.

The Ksp for a very insoluble salt is 4.2×10−47 at 298 K. What is ΔG∘ for the dissolution of the salt in water?

+265 kJ/mol

If ΔH = -60.0 kJ and ΔS = -0.400 kJ/K , the reaction is spontaneous below a certain temperature. Calculate that temperature.

150 K

CaO can be used as a drying agent. One such application occurs when water is added to dry concrete or cement. The reaction that occurs is CaO(s)+H2O(l)⇌Ca(OH)2(s) The product is commonly called slaked lime. Assuming the commonly used standard-state temperature of 25 ∘C, calculate ΔSuniv for this reaction using table from the table below. Substance S∘ [J/(K⋅mol)] ΔH∘f (kJ/mol) CaO(s) 39.9 −635.1 H2O(l) 69.9 −285.8 Ca(OH)2(s) 83.4 −986.1

193 JK

Given that ΔH∘=−92.38 kJ and ΔS∘=−198.3 J/K, what is the temperature above which the Haber ammonia process becomes nonspontaneous?

193 ∘C

Using the standard molar entropies below, calculate the standard entropy change, ΔS∘ , for the "water-splitting" reaction at 298 K: 2H2O(l) → 2H2(g) + O2(g) Standard Molar Entropies of Selected Substances at 298 K Substance S∘ (J/mol⋅K) H2(g) 130.6 O2(g) 205.0 H2O(g) 188.8 H2O(l) 69.9

326.4 J/K

As a system goes from state A to state B, its entropy decreases. What can you say about the number of microstates corresponding to each state?

A has more microstates than B

What is the difference between a state and a microstate of a system?

A microstate is a single possibility for all the positions and kinetic energies of all the molecules in a sample. A microstate is a snapshot of positions and speeds at a particular instant. A thermodynamic state is a set of conditions, usually temperature and pressure, that defines the properties of a bulk material.

Which of these statements is true?

All spontaneous reactions have a negative free energy change.

Explain your choice.

Both ΔHand ΔS for this reaction are positiveBoth Δ H and Δ S for this reaction are positive. The net change is breaking five blue-blue bonds. Enthalpies for this process are always positive. In the depicted reaction, both reactants and products are in the gas phase (they are far apart and randomly placed). There are twice as many molecules (or moles) of gas in the products, so Δ S is positive for this reaction..

Select each process that produces an increase in the entropy of the system:

CO2(s) → CO2(g)

Which of the following statements is true?

If Q>1, ΔG>ΔG∘.

The process of iron being oxidized to make iron(III) oxide (rust) is spontaneous. Which of these statements about this process is/are true?

Equilibrium is achieved in a closed system when the rate of iron oxidation is equal to the rate of iron(III) oxide reduction

Firefly luciferase is the enzyme that allows fireflies to illuminate their abdomens. Because this light generation is an ATP-requiring reaction, firefly luciferase can be used to test for the presence of ATP. In this way, luciferase can test for the presence of life. The coupled reactions are 1.2.luciferin+O2ATP⇌⇌oxyluciferin+lightAMP+PPiΔG∘=−31.6 kJ/mol If the overall ΔG∘ of the coupled reaction is -6.90 kJ/mol , what is the equilibrium constant, K, of the first reaction at 29 ∘C ?

K = 5.37×10−5

Consider a system consisting of a cylinder with a movable piston containing 106 gas molecules at 298 K at a volume of 1 L. Consider the following descriptions of this system, arrange them in order of increasing number of microstates in the resulting system

Most Microstates to Least Microstates: -Starting from the initial system, the gas reacts completely to produce 107 gas molecules at 395 K in a volume of 2 L -Starting from the initial system, the volume of the container is changed to 2 L and the temperature to 395 K -Starting from the initial system, the temperature is changed to 395 K at constant volume -Initial system, as stated in the problem statement. -Starting from the initial system, a combination reaction occurs at constant volume and temperature

If a process is nonspontaneous, does that mean the process cannot occur under any circumstances?

No

Does the entropy of the surroundings increase for spontaneous processes?

Not necessarily.

At what temperature are the two phases in equilibrium?

T = 100 ∘C

What can be said about the spontaneity of this reaction? Cdiamond→Cgraphite

The forward reaction is spontaneous at 298 K.

If a reaction is exothermic and its entropy change is positive, which statement is true?

The reaction is spontaneous at all temperatures.

A particular solvent with ΔS∘vap=112.9J/(K⋅mol) and ΔH∘vap=38.0kJ/mol is being considered for an experiment. In the experiment, which is to be run at 75 ∘C, the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not?

The solvent would not be suitable because ΔSuniv>0.

What can be said about the favorability of the overall reaction?

This reaction is thermodynamically favorable.

Gaseous Cl2 in the stratosphere to form gaseous Cl atoms.

ΔSsys>0

In what temperature range is it a spontaneous process?

above 100 ∘C

In what temperature range is it a nonspontaneous process?

below 100 ∘C

Which of the following processes are spontaneous, and which are nonspontaneous? (a) the ripening of a banana, (b) dissolution of sugar in a cup of hot coffee, (c) the reaction of nitrogen atoms to form N2 molecules at 25 ∘C and 1 atm, (d) lightning, (e) formation of CH4 and O2 molecules from CO2 and H2O at room temperature and 1 atm of pressure.

spontaneous: (a)(b)(c)(d) nonspontaneous: (e)

In which direction is this process exothermic?

the freezing of liquid water to ice

Consider these hypothetical chemical reactions: A⇌B,ΔG= 14.0 kJ/mol B⇌C,ΔG= -28.7 kJ/mol C⇌D,ΔG= 5.60 kJ/mol What is the free energy, ΔG, for the overall reaction, A⇌D?

ΔG = -9.10 kJmol

Calculate ΔG at 298 K if the reaction mixture consists of 41 atm of CH4, 0.010 atm of C3H8, and 1.9×10−2 atm of H2.

ΔG = 70 kJ

Using data from Appendix C in the textbook, calculate ΔG∘ at 298 K.

ΔG∘ = 128.9 kJ

The following chemical equations describe the same chemical reaction. How do the free energies of these two chemical equations compare? 2H2O(l) → 2H2(g) + O2(g) H2O(l) → H2(g) + 12O2(g)

ΔG∘1 = 2ΔG∘2

What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K? Cdiamond→Cgraphite Express your answer to three significant figures and include the appropriate units.

ΔG∘rxn = -2.90 kJ

Predict the sign of ΔH accompanying this reaction on the figure

ΔH>0

A gaseous system undergoes a change in temperature and volume. What is the entropy change for a particle in this system if the final number of microstates is 0.490 times that of the initial number of microstates?

ΔS = −9.84×10−24 J/(K⋅particle)

Predict the sign of ΔS accompanying reaction on the figure.

ΔS > 0

In a particular spontaneous process the entropy of the system decreases. What can you conclude about the sign and magnitude of ΔSsurr?

ΔSsurr is positive and greater than the magnitude of the decrease inΔSsys.

In a particular spontaneous process, the number of microstates available to the system decreases. What can you conclude about the sign of ΔSsurr?

ΔSsurr is positive.

During a certain reversible process, the surroundings undergo an entropy change, ΔSsurr = - 79 J/K . What is the entropy change of the system for this process?

ΔSsys = 79 J/K

Calcium phosphate precipitates upon mixing Ca(NO3)2(aq) and (NH4)3PO4(aq).

ΔSsys<0

Gaseous CO reacts with gaseous H2to form liquid methanol, CH3OH.

ΔSsys<0

Molten gold solidifies.

ΔSsys<0