Chem Semester Exam

**Insert table w/ five columns* The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. Which of the four acids listed in the table is hydrochloric acid? Responses

Acid 2

Samples of Fe and Al are heated from 25∘C to 75∘C. Based on the information in the table above, the change in the average kinetic energy of the atoms in the samples is

the same for both metal samples, because the initial and final temperatures are the same

A → X The enthalpy change for the reaction represented above is ΔHT. This reaction can be broken down into a series of steps as shown in the diagram: A relationship that must exist among the various enthalpy changes is

ΔHT - ΔH1 - ΔH2 - ΔH3 = 0

The reaction between AgNO3 and CaCl2 is represented by the equation above, and the table provides the approximate S° values for the reactants and products. Which of the following is the approximate ΔS° for the reaction?

−68 J/molrxn⋅K

Based on the information in the table above, which of the following shows the cell potential and the Gibbs free energy change for the overall reaction that occurs in a standard galvanic

+1.63/-944

A student mixes 100.mL of 0.25M HCl (aq) with 200.mL of 0.50M HClO4 (aq) and then dilutes the mixture with distilled water to a total volume of 500.mL. The [H3O+] in the final solution is closest to

0.25 M

The equation and standard cell potential for the decomposition of H2O2(aq) in acidic solution at 25°C is given above. The reduction half-reactions for the process are listed below. What is the standard reduction potential for the half-reaction represented above?

+0.68 V

Al3+(aq) + 3 e- → Al(s) E° = -1.66 V Ag+(aq) + e- → Ag(s) E° = +0.80 V According to the standard reduction potentials given above, what is the standard cell potential for the reaction represented below? 3 Ag+(aq) + Al(s) → 3 Ag(s) + Al3+(aq)

+2.46 V

A 2.00mol sample of C2H5OH undergoes the phase transition illustrated in the diagram above. The molar enthalpy of vaporization, ΔHvap, of C2H5OH is +38.6kJ/mol. Which of the following best identifies the change in enthalpy in the phase transition shown in the diagram?

- 77.2 kJ

Reaction 1 : 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l) ΔG ° = -1010 kJ/molrxn Reaction 2 : 2 NO2(g) → 2 NO(g) + O2(g) ΔG ° = 70 kJ/molrxn Reaction 3 : 4 NO2(g) + O2(g) + 2 H2O(l) → 4 HNO3(aq) ΔG ° = -170 kJ/molrxn Based on the values of ΔG° for the three reactions represented above, what is the value of ΔG° for the reaction represented below? 4 NH3(g) + 8 O2(g) → 4 HNO3(aq) + 4 H2O(l)

-1320 kJ/molrxn

Based on the Ka values listed in the table above, equal volumes of which of the following pairs of solutions when mixed together will result in a buffer solution with a pH between 7 and 8 ?

0.10M HClO(aq) and 0.10M NaClO(aq)

X2(g) + Y2(g) ⇄ 2 XY(g) Kc = 3.0 A mixture of X2(g), Y2(g) and XY(g) is placed in a previously evacuated, rigid container and allowed to reach equilibrium at a constant temperature, as shown above. Which of the following sets of initial concentrations would lead to the formation of more product as the system moves toward equilibrium?

0.50M/0.45M/0.20M

NH3(aq) + CH3NH3+(aq) ⇄ NH4+(aq) + CH3NH2(aq) Keq=0.041 Which of the following species is the strongest base in the reaction represented above?

CH3NH2(aq)

The table above shows the values of Ka for four weak acids. Which of the following pairs of chemical species, when combined in equimolar amounts, results in a buffer with a pH closest to 7.5 ?

HClO and ClO−

2 NO(g) + O2(g) ⇄ 2 NO2(g) ΔH < 0 Which of the following changes alone would cause a decrease in the value of Keq for the reaction represented above?

Increasing the temperature

X(g) + Y(g) ⇄ 2Z(g) When 4.00 mol each of X(g) and Y(g) are placed in a 1.00 L vessel and allowed to react at constant temperature according to the equation above, 6.00 mol of Z(g) is produced. What is the value of the equilibrium constant, Kc ?

36

The graph above shows the titration curve that resulted when a sample of 0.1 M monoprotic acid was titrated with a solution of NaOH. Based on the graph, the pKa of the acid is closest to

4.0

½ H2(g) + ½ I2(s) → HI(g) ∆H = 26 kJ/molrxn ½ H2(g) + ½ I2(g) → HI(g ) ∆H = −5.0 kJ/molrxn Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below? I2(s) → I2(g)

62 kJ/molrxn

2 NO2(g) ⇄ N2O4(g) dark brown colorless The dimerization of NO2(g) , an exothermic process, is represented by the equation above. A 0.0688 mol sample of NO2(g) is placed in a rigid 1.00 L reaction vessel and allowed to reach equilibrium at a certain temperature. What is the value of Kc at this temperature if 0.0133 mol of N2O4(g) is present at equilibrium?

7.47

**Insert table w/ 5 column** The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. If equal volumes of the four acids at a concentration of 0.50 M are each titrated with a strong base, which will require the greatest volume of base to reach the equivalence point?

All the acids will require the same volume of base to reach the equivalence point.

2H2O(l) ⇄ H3O+(aq) + OH−(aq) ΔH°=+ 56kJ/molrxn The endothermic autoionization of pure water is represented by the chemical equation shown above. The pH of pure water is measured to be 7.00 at 25.0°C and 6.02 at 100.0°C. Which of the following statements best explains these observations?

At the higher temperature water dissociates more, [H3O+] = [OH−], and the water remains neutral.

A 1.0mol sample of He(g) at 25°C is mixed with a .0mol sample of Xe(g) at 50°C. Which of the following correctly predicts the changes in average kinetic energy and the average speed of the Xe(g) atoms that will occur as the mixture approaches thermal equilibrium?

Average KE of Xe atoms: will decrease Average speed of Xe atoms: will decrease

A 0.10M solution of a weak acid is titrated with 0.10MNaOH(aq). Based on the titration curve above, which of the following could be the identity of the weak acid?

CH3CH2COOH with a Ka value of 1×10−5

A solution is prepared by adding 100 mL of 1.0 M HC2H3O2(aq) to 100 mL of 1.0 M NaC2H3O2(aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0 M HCl are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH?

H3O+(aq) + C2H3O2-(aq) → HC2H3O2(aq) +H2O(l)

The graph below shows the titration curve that results when 100. mL of 0.0250 M acetic acid is titrated with 0.100 M NaOH. Which of the following indicators is the best choice for this titration?

Indicator Phenolphthalein pH Range of Color Change n8.2 - 10.0

Which of the following statements is true for the equilibrium vapor pressure of a liquid in a closed system?

It is independent of the volume of the vapor phase.

A sample of CHCl3(s) was exposed to a constant source of heat for a period of time. The graph above shows the change in the temperature of the sample as heat is added. Which of the following best describes what occurs at the particle level that makes segment D longer than segment B?

The enthalpy of vaporization is greater than the enthalpy of fusion, because separating molecules completely from the liquid to form a gas requires more energy than separating molecules from their bound crystalline state to a liquid state.

H2(g) + I2(g) ⇄ 2HI(g) Hydrogen gas reacts with iodine gas at constant temperature in a sealed rigid container. The gases are allowed to reach equilibrium according to the equation above. Which of the following best describes what will happen to the reaction immediately after additional iodine gas is added to the system?

The rate of the forward reaction becomes greater than the rate of the reverse reaction.

Li3N(s) + 2 H2(g) ⇄ LiNH2(s) + 2 LiH(s) ΔH° = -192 kJ/molrxn Because pure H2 is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C. Which of the following is the most likely reason that the reaction occurs at a significant rate only if the temperature of the reaction mixture is greater than 200°C?

The reaction has a high activation energy.

When a magnesium wire is dipped into a solution of lead (II) nitrate, a black deposit forms on the wire. Which of the following can be concluded from this observation?

The standard reduction potential, E°, for Pb2+(aq) is greater than that for Mg2+(aq).

CH4(g) + 2O2 (g) -> CO2(g) + 2H2O (g) Delta H* < 0 Which of the following statements must be true for the combustion of CH4(g), represented by the equation above?

The sum of the bond dissociation energies of the product molecules is greater than the sum of the bond dissociation energies of the reactant molecules.

The graphs above show Maxwell-Boltzmann distributions for one-mole samples of Ar(g). Graph 1 shows the distribution of particle energies at 300K and graph 2 shows the distribution of particle energies at 600K. A student predicts that if the samples are combined in an insulated container and thermal equilibrium is attained, then the most probable particle energy will be between the most probable energy shown in graph 1 and the most probable energy shown in graph 2. Which of the following is the best justification for the student's claim?

When the samples are combined, the gas particles will collide with one another, with the net effect being that energy will be transferred from the more energetic particles to the less energetic particles until a new distribution of energies is achieved at a temperature between 300K and 600K.

Kw = [H3O+][OH−] = 1.0×10−14 at 25°C Based on the information above, which of the following is true for a sample of pure water at 25°C?

pOH = 7.00

3 C2H2(g) → C6H6(g) What is the standard enthalpy change ΔHo, for the reaction represented above? (ΔHof of C2H2(g) is 230 kJ mol-1) (ΔHof of C6H6(g) is 83 kJ mol-1)

− 607 kJ

4 NH3(g) + 3 O2(g) → 2 N2(g) + 6 H2O(g) If the standard molar heats of formation of ammonia, NH3(g), and gaseous water, H2O(g), are −46 kJ/mol and −242 kJ/mol, respectively, what is the value of ΔH° for the reaction represented above?

−1,270 kJ/molrxn

Reaction 1: 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l) ΔG ° = -1010 kJ/molrxn Reaction 2: 2 NO2(g) → 2 NO(g) + O2(g) ΔG ° = 70 kJ/molrxn Reaction 3: 4 NO2(g) + O2(g) + 2 H2O(l) → 4 HNO3(aq) ΔG ° = -170 kJ/molrxn Based on the values of ΔG° for the three reactions represented above, what is the value of ΔG° for the reaction represented below? 4 NH3(g) + 8 O2(g) → 4 HNO3(aq) + 4 H2O(l)

-1320 kJ/molrxn

Which of the following best describes the flow of heat when 1.0 mol of XY2 decomposes?

50 kJ of heat is transferred from the surroundings.

Caffeine (C8H10N4O2) is a weak base with a Kb value of 4 x 10-4. The pH of a 0.01 M solution of caffeine is in the range of

11-12

The diagram above represents the melting of H2O(s). A 2.00 mole sample of H2O(s) at 0°C melted, producing H2O(l) at 0°C. Based on the diagram, which of the following best describes the amount of heat required for this process and the changes that took place at the molecular level?

12.0 kJ of heat was absorbed to overcome some of the hydrogen bonding forces holding the water molecules in fixed positions in the crystalline structure.

H2(g) + I2(g) ⇄ 2HI(g) At 450oC, 2.0 moles each of H2(g), I2(g), and HI(g) are combined in a 1.0 L rigid container. The value of Kc at 450oC is 50. Which of the following will occur as the system moves toward equilibrium?

More HI(g) will form.

**LOTS of beakers and other complex stuff** The values of the dissociation constants for H3PO4 are given in the table above. Given that the solution in the beaker at the end of step 2 had a pH of approximately 1, which of the following chemical species had the lowest concentration among the products of step 2 ?

PO43-(aq)

When a strong acid is titrated with a strong base using phenolphthalein as an indicator, the color changes abruptly at the endpoint of the titration and can be switched back and forth by the addition of only one drop of acid or base. The reason for the abruptness of this color change is that

a large change in pH occurs near the endpoint of the titration

FeF2(s) ⇄ Fe2+(aq) + 2 F-(aq) K1 = 2 × 10-6 F-(aq) + H+(aq) ⇄ HF(aq) K2 = 1 × 103 FeF2(s) + 2 H+(aq) ⇄ Fe2+(aq) + 2 HF(aq) K3 = ? On the basis of the information above, the dissolution of FeF2(s) in acidic solution is

thermodynamically favorable, because K3 > 1

2X(g) + Y(g) ⇄ 3Z(g) The reaction mixture represented above is at equilibrium at 298 K, and the molar concentrations are [X] = 2.0 M, [Y] = 0.5 M, and [Z] = 4.0 M. What is the value of the equilibrium constant for the reaction at 298 K ?

32

The pH of a 0.01 M HNO2 (aq) solution is in which of the following ranges? (For HNO2 (aq), Ka = 4.0 x 10-4)

Between 2 and 3

Addition of sulfurous acid (a weak acid) to barium hydroxide (a strong base) results in the formation of a precipitate. The net ionic equation for this reaction is

H2SO3(aq) + Ba2+(aq) + 2 OH-(aq) ⇄ BaSO3(s) + 2 H2O(l)

A 0.1M aqueous solution of which of the acids shown in the table above would have a pH closest to 7.0, and why?

HIO, because IΙ has the lowest electronegativity.

Which of the following statements best explains the trend in the molar solubility of CaF2(s) in various concentrations of NaF(aq) shown in the graph above?

Higher concentrations of F−(aq) allow less CaF2(s) to dissolve before the solution becomes saturated. Higher concentrations of F, −, (aq) allow less CaF, 2, (s) to dissolve before the solution becomes saturated.

CH3OH (g) -> CO (g) +2H2 (g) delta H = +91 kj/molrxn The reaction represented above goes essentially to completion. The reaction takes place in a rigid, insulated vessel that is initially at 600 K What can be inferred about ∆S° for the reaction at 600 K?

It must be positive, since ∆G° is negative and ∆H° is positive.

The oxidation of PCl3(g) is represented by the equation above, and the table provides the approximate values of the absolute molar entropies, S°, for these substances. Based on the information given, what is the approximate ΔS° for the reaction?

−170 J/molrxn⋅K

A sample of a solid organic compound is completely combusted in a calorimeter. The heat generated by combustion is transferred to the water, causing the temperature of the water to increase. Based on the data in the table above, which of the following is the best estimate of the heat of combustion, ΔHcomb, of the organic solid? (The specific heat of water is 4.2J/(g⋅°C))

−18 kJ/g

In an insulated cup of negligible heat capacity, 50. g of water at 40.°C is mixed with 30. g of water at 20.°C. The final temperature of the mixture is closest to Responses

33°C

A cube of ice is added to some hot water in a rigid, insulated container, which is then sealed. There is no heat exchange with the surroundings. What has happened to the total energy and the total entropy when the system reaches equilibrium?

Energy: Remains Constant Entropy: Increases

Which of the following is a list of the minimum amount of data needed for determining the molar enthalpy of solution of KCl(s) in pure H2O(l)? (Assume that the KCl(aq) has the same specific heat capacity as pure water and that the initial temperatures of the KCl(s) and the water are the same.)

Mass of KCl(s), mass of H2O, initial temperature of the water, and final temperature of the solution

The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) → 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstance? The silver electrode is made larger.

No change in voltage occurs

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, ΔH, for each step?

Steps 1 and 2 are endothermic, and the final step is exothermic.

Zn(s) + Cu2+ ⇌ Zn2+ + Cu(s) An electrolytic cell based on the reaction represented above was constructed from zinc and copper half-cells. The observed voltage was found to be 1.00 volt instead of the standard cell potential, E0, of 1.10 volts. Which of the following could correctly account for this observation?

The Zn2+ solution was more concentrated than the Cu2+ solution.

A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water, and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g⋅°C).)

The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.

NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq) A student is trying to determine the heat of reaction for the acid-base neutralization reaction represented above. The student uses 0.50 M NaOH and 0.50 M HCl solutions. Which of the following situations, by itself, would most likely result in the LEAST error in the calculated value of the heat of reaction?

The thermometer was incorrectly calibrated and read 0.5 Celsius degree too high during the procedure.

What is the molar solubility in water of Ag2CrO4 ? (The Ksp for Ag2CrO4 is 8 x 10-12.)

3√2×10−12M

2 H2O(l) ⇄ H3O+(aq) + OH-(aq) The autoionization of water is represented by the equation above. Values of pKw at various temperatures are listed in the table below. Based on the information above, which of the following statements is true?

As the temperature increases, the pH of pure water decreases.

The standard reduction potentials for the half-reactions related to the galvanic cell represented above are listed in the table below. Which of the following gives the value of E°cell for the cell?

E°cell = +0.02 V

Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [CI-]?

PbCl2

Acid-dissociation constants of two acids are listed in the table above. A 20. mL sample of a 0.10 M solution of each acid is titrated to the equivalence point with 20. mL of 0.10 M NaOH. Which of the following is a true statement about the pH of the solutions at the equivalence point?

Solution 1 has a higher pH at the equivalence point because CH3CO2H has the stronger conjugate base.

A 100 g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100 g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded? Responses

The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

Beaker X contains 50mL of distilled water and beaker Y contains 100mL of 1.0M NaCl. Solid AgCl is added to each of the beakers. After thoroughly stirring the contents of the beakers, some solid AgCl remains at the bottom of each beaker, as shown above. Which of the following is true?

[Ag+] is greater in beaker X.

The following questions relate to the graph below. The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase. The substance is at its normal freezing point at time

t2

CaCO3(s) ⇄ CaO(s) + CO2(g) ΔH° = 178 kJ/molrxn The reaction system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system? Responses

Lowering the temperature of the system

COCl2(g) ⇄ CO(g) + Cl2(g) COCl2(g) decomposes according to the equation above. When pure COCl2(g) is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of Kp for the reaction at 690 K?

0.050

A 20.0mL sample of a 0.125M monoprotic acid solution is titrated with a NaOH(aq) solution of unknown concentration. Based on the titration curve above, what is the molar concentration of the NaOH(aq) solution?

0.250 M

ICl(g) ⇄ ½ I2(g) + ½ Cl2 (g) Keq = 0.1 Based on the information above, what is the value of Keq for the reaction represented below? I2(g) + Cl2 (g) ⇄ 2 ICl(g)

100

For which of the following reaction mixtures at equilibrium would reducing the volume of the container at constant temperature cause the equilibrium to shift toward the products?

2 NO2(g) ⇄ N2O4(g)

For an experiment, 50.0g of H2O was added to a coffee-cup calorimeter, as shown in the diagram above. The initial temperature of the H2O was 22.0°C, and it absorbed 300.J of heat from an object that was carefully placed inside the calorimeter. Assuming no heat is transferred to the surroundings, which of the following was the approximate temperature of the H2O after thermal equilibrium was reached? Assume that the specific heat capacity of H2O is 4.2J/(g⋅K).

23.4°C

Standard reduction potentials for the half-reactions associated with the electrochemical cell shown above are given in the table below. Half-Reaction E°(V) Ag+(aq)+e−→Ag(s) +0.80 Zn2+(aq)+2e−→Zn(s) −0.76 Which of the following is the net ionic equation for the overall reaction that occurs as the cell operates?

2Ag+(aq) + Zn(s) → 2Ag(s) + Zn2+(aq)

HC4H7O2(aq) + H2O(l) ⇄ H3O+(aq) + C4H7O2−(aq) The chemical equation above represents the acid ionization equilibrium for HC4H7O2 for which pKa = 4.8. Which of the following is the best estimate for the pH of a buffer prepared by mixing 100.mL of 0.20M HC4H7O2 with 100.mL of 0.10M NaC4H7O2?

4.5

In the electroplating of nickel, 0.200 faraday of electrical charge is passed through a solution of NiSO4. What mass of nickel is deposited?

5.87 g

N2(g) + 3 H2(g) ⇄ 2 NH3(g) ΔH∘298 = -92 kJ/molrxn; ΔG∘298 = -33 kJ/molrxn Consider the reaction represented above at 298 K. When equal volumes of N2(g) and H2(g), each at 1 atm, are mixed in a closed container at 298 K, no formation of NH3(g) is observed. Which of the following best explains the observation?

A high activation energy makes the forward reaction extremely slow at 298 K.

H2O(l) + H2O(l) ⇄ H3O+(aq) + OH−(aq) Kw=7.0×10−14 at 55° Pure water autoionizes as shown in the equation above. Based on this information, which of the following is correct?

At 55°C, pH=−log(√kw) for pure water.

Cu2+(aq) + 2 e- → Cu(s) E° = 0.34 V Cr3+(aq) + e- → Cr2+(aq) E° = -0.41 V According to the half-reactions represented above, which of the following occurs in aqueous solutions under standard conditions?

Cu2+(aq) + 2 Cr2+(aq) → Cu(s) + 2 Cr3+(aq)

Mg(OH)2(s) ⇄ Mg2+(aq) + 2 OH- (aq) The exothermic dissolution of Mg(OH)2(s) in water is represented by the equation above. The Ksp of Mg(OH)2 is 1.8 x 10-11. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?

Decreasing the pH

2H2O2 (aq) --> 2H2O (l) + O2 (g) E=0.55 V The equation and standard cell potential for the decomposition of H2O2(aq) in acidic solution at 25°C is given above. The reduction half-reactions for the process are listed below. O2 (g) + 4H+(aq) + 4e- --> 2H2O (l) E=1.23V O2 (g) + 2H+ (aq) + 2e- --> H2O2(aq) E=? Which of the following is true for the decomposition of H2O2(aq)?

Delta G > 0 Keq > 1

Mixtures that would be considered buffers include which of the following? I. 0.10 M HCl + 0.10 M NaCl II. 0.10 M HF + 0.10 M NaF III. 0.10 M HBr + 0.10 M NaBr

II Only

High solubility of an ionic solid in water is favored by which of the following conditions? I. The existence of strong ionic attractions in the crystal lattice II. The formation of strong ion-dipole attractions III. An increase in entropy upon dissolving

II and III only

Fe3+(aq) + SCN-(aq) ⇄ Fe(SCN)2+(aq) For the reaction represented above, the value of the equilibrium constant, Keq, is 240 at 25°C. From this information, correct deductions about the reaction at 25°C include which of the following? I. The reaction is quite rapid. II. The product is favored over the reactants at equilibrium. III. The reaction is endothermic.

II only

Which of the following particulate representations shows a process during which the entropy of the system decreases?

In cylinders, far apart to condensed

An equimolar mixture of X(g) and Y(g) is placed inside a rigid container at constant temperature. The particle diagram above represents the changes that occur over time. Based on the particle diagram, which of the following best predicts whether or not the system has reached equilibrium by 300 s?

It is not possible to determine that the system has reached equilibrium by 300 s because the amounts of X, Y, and XY have continued to change.

Based on the information above, which of the following expressions represents the equilibrium constant, K, for the reaction represented by the equation below? La3+ + CO32− ⇄ LaCO3+

K = (K1)(Kw) / (Ka)

Refer to the following. PCl5(g) ⇄ PCl3(g)+Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Which of the following statements about Kp, the equilibrium constant for the reaction, is correct?

Kp < 1

Which of the following phase changes involves the transfer of heat from the surroundings to the system?

NH3(l)→NH3(g), because NH3 molecules in the liquid phase must absorb energy in order to overcome their intermolecular attractions and become free gas molecules.

2 H2(g) + O2(g) → 2 H2O(g) For the reaction represented above at 25°C, what are the signs of ΔH°, ΔS°, and ΔG°?

Negative all across!

2NO(g) + Br2(g) ⇄ 2NOBr(g) Kp=(PNOBr)2/(PNO)2(PBr2)=28 The system represented by the equation above is allowed to establish equilibrium. The initial pressures of the substances are given in the table. Which of the following explains what the system will do as it approaches equilibrium? Responses

Q=(80.)2/(10.)2(2.0)>Kp and equilibrium will be approached by consuming NOBr because the reverse reaction is faster than the forward reaction.

Half-cell 1: strip of Al(s) in 1.00 M Al(NO3)3(aq)Half-cell 2: strip of Cu(s) in 1.00 M Cu(NO3)2(aq)Half-cell 3: strip of Fe(s) in 1.00 M Fe(NO3)2(aq) In galvanic cells Y and Z, which of the following takes place in half-cell 3 ?

Reduction occurs in cell Y, and oxidation occurs in cell Z.

A 100g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded?

The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase. Which of the following best describes what happens to the substance between t4 and t5?

The molecules are leaving the liquid phase.

**Insert table w/ 5 column** The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. A 25 mL sample of a 1.0 M solution of acid 1 is mixed with 25 mL of 0.50 M NaOH. Which of the following best explains what happens to the pH of the mixture when a few drops of 1.0 M HNO3 are added?

The pH of the mixture stays about the same, because the conjugate base of acid 1 reacts with the added H3O+ ions.

2X(g) + Y2(g) ⇄ 2XY(g) A reversible reaction is represented by the equation above. The amounts of reactants and products at time 1 are shown in the particle diagram on the left. The particle diagram on the right shows the amounts of reactants and products at time 2. Based on the diagrams, what can be inferred about the relative rates of the forward and reverse reactions between time 1 and time 2 ?

The rate of the forward reaction is greater than the rate of the reverse reaction.

The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate. Which of the following explains why the slope of segment T is greater than the slope of segment R?

The specific heat capacity of the gaseous ethanol is less than the specific heat capacity of liquid ethanol.

In an experiment to estimate the enthalpy change of a reaction, a student makes two aqueous solutions, each containing one of the reactants. The student combines the solutions, both originally at the same temperature, in a calorimeter and records the final temperature of the mixture. In addition to the masses of the solutions and the temperature change of the mixture, which of the following pieces of information does the student need to calculate the enthalpy change of the reaction?

The specific heat capacity of the reaction mixture

H2(g) + Cl2(g) ⇄ 2 HCl(g) Kp = 2 × 1030 at 298 K HCl(g) can be synthesized from H2(g) and Cl2(g) as represented above. A student studying the kinetics of the reaction proposes the following mechanism Step 1: Cl2(g) → 2 Cl(g) (slow) ∆H° = 242 kJ/molrxn Step 2: H2(g) + Cl(g) → HCl(g) + H(g) (fast) ∆H° = 4 kJ/molrxn Step 3: H(g) + Cl(g) → HCl(g) (fast) ∆H° = -432 kJ/molrxn Which of the following statements identifies the greatest single reason that the value of Kp for the overall reaction at 298 K has such a large magnitude?

The value of ΔH° for the overall reaction is large and negative.

A 30.g sample of Al(s) is heated to 50°C and placed in a calorimeter containing 150g of water at 20°C. As the system approaches thermal equilibrium, energy is transferred

from the Al(s) to the water and the temperature of the Al(s) decreases

2 H2O2(aq) → 2 H2O(l) + O2(g) ΔH° = −196 kJ/molrxn The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300. K and recorded the concentration of H2O2 as a function of time. The results are given in the table below. The reaction is thermodynamically favorable. The signs of ΔG° and ΔS° for the reaction are which of the following?

negative/positive

2 NO2(g) ⇄ N2O4(g) Kc = 200 The equilibrium system shown above is represented in the diagram below in which each molecule represents one mole of the substance in a 100.L100.L container at a constant temperature. Additional N2O4(g) is added to the container and allowed to reestablish equilibrium. Which of the following best represents the system after the equilibrium has been reestablished?

the one with a lot of compounds