AP CHEM FINAL REVIEW

The process of dissolution of NaCl(s) in H2O(l) is represented in the diagram above. Which of the following summarizes the signs of (delta)H and (delta)S for each part of the dissolution process.

(ANSWERS ARE IN A TABLE) Positive for both H and S in solvent-solvent and solute-solute. Neg for both H and S in solute solvent interactions

Which of the following statements about (delta)H for the reaction is correct

(delta)H>0 because energy is required to break the N-N bond

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?

+0.20V

Reaction 1: 4NH₃(g)+5O₂(g) -> 4NO₂(g) + 6H₂O(l) ∆G⁰=-1010 kJ/mol rxn Reaction 2: 2NO₂(g) -> 2NO +O₂ ∆G⁰=70kJ/mol rxn Reaction 3: 4NO₂(g)+O₂(g)+2H₂O(l) -> 4HNO₃(aq) ∆G⁰=-170 kJ/mol rxn Based on the values of the ∆G⁰ for the three reactions represented above, what is the value of ∆G⁰ for the reaction represented below? 4NH₃(g)+8O₂(g) -> 4HNO₃(aq) + 4H₂O(l)

-1320 kJ/mol rxn

Fe³⁺ (aq) +KSCN(s)->FeSCN²⁺(aq)+K⁺(aq) To determine the moles of Fe3+(aq) in a 100mL sample of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species, FeSCN2+(aq), as represented by the equation above. The absorbance of FeSCN2+(aq) a different concentration is shown in the graph to the right. (IMAGE) If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100 mL sample?(Assume that any volume change due to adding the KSCN(s) is negligible.)

4 x 10⁻⁶

On the basis of the pH curve, the pKa value of the acid is closest to

5

Which of the following best describes the change that takes place immediately after the CH₃OH(l) is introduced into the previously evacuated vessel?

A physical change takes place because intermolecular attractions are overcome.

A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings.

A weak acid was titrated with a strong base, as evidenced by the equivalence point pH> 7.

NH3 reacts with BF3 to form a single species. Which of the following structural diagrams is the most likely representation of the product of the reaction?

ALL ANSWERS ARE DIAGRAMS. Chose the one with N and B in the middle, surrounded by H and F

An acetate buffer solution is prepared by combining 50 mL of 0.20 M acetic acid, HC2H3O2(aq), and 50 mL and 0.20 M sodium acetate, NaC2H3O2(aq). A 5.0 mL sample of 0.1 M NaOH(aq) is added to the buffer solution. Which is the following is a correct pairing of the acetate species present in greater concentration and the pH of the solution after the NaOH(aq) is added?

Acetate Species=C2H3O2- pH=>4.7

ClO2-(aq)+HCOOH(aq)<-> HClO2(aq)+HCOO-(aq) Keq<1 What are the relative strengths of the acids and bases in the reaction represented by the equation above?

Acid Strength= HClO2>HCOOH Base Strength=ClO2-<HCOO-

Which of the following best help explain why an increase in temperature increases the rate of a chemical reaction?

At higher temperatures , high energy collisions happen more frequently.

In which of the following liquids do the intermolecular forces include dipole-dipole forces?

CH2F2 (l)

When a small amount of 12 M HNO₃ is added to a buffer solution made by mixing CH₃NH₂ and CH₃NH₃Cl, the pH of the buffer solution changes from 10.64 to 10.62. Which of the following equations represents the reaction that accounts for the fact that the pH does not change significantly when the HNO₃ is added.

CH₃NH₂+H⁺→CH₃NH₃⁺

Based on structures shown above, (IMAGE) which of the following statements identifies the compound with the highest boiling point and provides the best explanation for the higher boiling point?

Compound 2, because it forms hydrogen bonds, whereas compound 1 does not.

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

Decreasing the pH

(Half reactions are given) Based on the formation in the table above, which of the following shows that the cell potential and Gibbs free energy change for the overall reaction that occurs in a standard galvanic cell?

E=+1.63 G=-944

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

Gas to Solid

Which of the following most likely describes the solid represented in the diagram to the left?

It is a brittle, water-soluble electrolyte that is a poor thermal and electrical conductor as a solid.

Cu(S)+ 4HNO3(aq)-->Cu(NO3)2(aq)+2NO2(g)+2H2O(l) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in fume hood. The students slowly poured 15.0 mL of 15.8 M HNO3 (aq) into their beakers. the reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indication the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. Which of the following is true about the reaction?

It is a redox reaction, because Cu(s) is oxidized and the nitrogen atom in NO3-(aq) is reduced

Two molecules of the amino acid glycine join through the formation of a peptide bond, as shown above. The thermodynamic data for the reaction are listed in the following table (IMAGE AND TABLE) Under which of the following temperature conditions is the reaction thermodynamically favored?

It is not favored at any temperature

CH3OH (g) = CO (g) + 2H2 (g) 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 600K. What can be inferred about delta S for the reaction at 600K?

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

(REACTION TABLE WITH Keq GIVEN) 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

The forward reaction is thermodynamically favored at which of the following temperatures?

Low temperatures only

Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(l) is a good conductor of electricity?

MgO(s) consists of separate Mg2+ ions and O2- ions held in a fixed lattice, but in MgO(l) the ions are free to move and conduct electricity.

H₂(g) + I₂(g) ⇌ 2HI(g) Kc=50 at 600°C Equimolar samples of each of the three gasses, H₂(g), I₂(g) and HI(g), are introduced in a 3.0 L container that is heated to 600°C. According to the information above, which of the following will occur as the system approaches equilibrium?

More HI(g) will be produced because Q<Kc

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water.

NH3

Three substances were studied in the laboratory, and the data in the table above was collected. Based on the data, which of the following shows the type of bonding in each substance?

Network covalent, Metallic, Ionic

For which of the equilibrium systems represented below will the amount of the products at equilibrium increase if the volume of the reaction vessel is increased at a constant temperature?

PCl₅⇌PCl₃+Cl₂

The values of the dissociation constants for the H₃PO₄ are given in the table to the left. Given that the solution in the beaker at the end of step 2 had a pH of about 1, which of the following chemical species had the lowest concentration among the products of step 2?

PO₄³⁻

Equilmolar samples of Pb(OH)₂, PbF₂ and PbF₂ are placed in three separate beakers, each containing 250 mL of water at 25°C. After the solutions are stirred solid remains in the bottom of each beaker. Based on the Ksp values for the compounds listed in the table below, a solution of which of the compounds will have the lowest [Pb²⁺]?

Pb(OH)₂

Based on the information in the table to the left, which of the compounds has the highest boiling point, and why?

Propanoic acid, because it can form intermolecular hydrogen bonds

NO2(g)+CO(g)->NO(g)+CO2(g) The reaction between NO2(g) and CO(g) is represented above. The elementary steps of a proposed mechanism are represented below. Step 1: 2NO2(g)-> NO(g) _NO3(g) Slow Step 2: NO3(g) +CO(g)->NO2(g)+CO2(g) fast Which of the following is the rate law for the overall reaction that is consistent with the proposed mechanism?

Rate=k[NO2]2

(4 reactions are given, A-D) The reactions represented above are carried out in sealed, rigid container and allowed to reach equilibrium. If the volume of each container is reduced from 1.0 L to .5 L at constant temperature, for which of the reactions will the amount of products be increased

Reaction A

The step-wise dissociation of selenous acid, H₂SeO₃ is represented by the equations above. Which of the following best helps explain why the value of Ka₂ is so much smaller than the value of Ka₁

Removing the first H⁺from H₂SeO₃ requires less energy than removing the second H⁺, because the second H⁺ is removed from a negatively charged species.

(TABLE ) Acid dissociation constants of two acids are listed in the table above. A 20 mL sample of a 0.1 M solution of each acid is titrated to equivalence point with 20 mL of 0.1 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 a stronger conjugate base.

What will be the effect on the amount of gas produced if the experiment is repeated using 0.35g of K(s) instead of 0.35 g of Li(s)?

Some gas will be produced but less than the amount of gas produced with Li(s)

Which of the following experimental techniques will allow the most accurate determination of the concentration of NO₂(g) at equilibrium?

Spectrophotometry

A student is given a sample of a pure, white crystalline substance. Which of the following would be most useful in providing data to determine if the substance is an ionic compound?

Testing the electrical conductivity of an aqueous solution of the substance

Which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath.

The forward reaction is endothermic

Cl-(aq)+CLO-(aq)+2H(aw)->CL2(g) +H2O(l) What effect will increasing [H+] at constant temp have on the reaction represented above?

The frequency of collisions between H+(aq) ions and ClO- (aq) ions will increase.

Cr2O7² ⁻(aq) + H2O (l)<->2CrO4² ⁻(aq)+2H3O+(aq) orange yellow The equilibrium system represented by the equation above initially contains equal concentrations of Cr2O7² ⁻(aq) and 2CrO4² ⁻(aq). Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH(aq) to the system and provides an explanation?

The mixture will become more yellow because OH-(aq) will shift the equilibrium toward products

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.

2H2(g)+O2(g)->H2O(g) When H2(g) and O2(g) are mixed together in a rigid reaction vessel at 25C, no reaction occurs. When the mixture is sparked, however, the gases react vigorously according to the equation above, releasing heat. Which of the following statements correctly explains why the spark is needed for the reaction to occur when the gases are originally at 25C?

The reaction has a large activation energy at 25C

2XY(g)<->X2(g)+Y2(g) Kp=230 A certain gas, XY(g), decomposes as represented by the equation above. A sample of each of the three gases is put in the three gases is put in a previously evacuated container. The initial partial pressures of the gases are shown in the table below. (TABLE) The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?

The reaction will form more reactant

In one student's experiment the reaction proceeded at a much slower rate than it did in the other students' experiments. Which of the following could explain the slower reaction rate?

The students used a 1.5 M solution of HNO3(aq) instead of 15.8 M solution of HNO3(aq)

CH3OH (g) = CO (g) + 2H2 (g) 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 600K. What happens to the temperature of he contents of the vessel as the reaction occurs?

The temperature must decrease, because the reaction is endothermic.

H2(g)+Cl2(g)<->2HCl(g) Kp=2E30 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. (3 steps listed out, too tired to type them, sorry) 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 (delta) H for the overall reaction is large and negative

Which of the following best helps to explain why CCl₄ is a liquid whereas CI₄ is a solid when both are at 25°C?

Thee London Dispersion forces are stronger in CI₄ than in CCl₄ because CI₄ has a more polarizable electron cloud than CCl₄.

Benzene, C6H6, has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best described the intermolecular forces of attraction between water and benzene?

There are dipole-induced dipole and london dispersion interactions between water and benzene

(ANOTHER TABLE GIVEN) Three saturated solutions (X,Y, and Z) are prepared at 25C. Based on the information in the table above, which of the following lists the solutions in order of increasing [Ag+]?

Z<X<Y

CO (g) + 2H2 (g) = CH3OH (g) H<0 The synthesis of CH3OH (g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483K is 14.5. A 1.0 mol sample of CO (g) and a 1.0 mol mol sample of H2 (g) are pumped into a rigid, previously evacuated 2.0 L reaction vessel at 483K. Which of the following must be true at equilibrium?

[H2] < [CO2]

A 1.0 L sample of a pure gas is found to have a lower pressure than that predicted by the ideal gas law. The best explanation for the observation is that the molecules of the gas

are attracted to each other and do not exert as much force on the container walls as they would if they had no mutual attractions

At 298 k and 1 atm, Br₂ is a liquid with a high vapor pressure, and Cl₂ is a gas. Those observations provide evidence that under the given conditions, the

forces among Br₂ molecules are stronger than those among Cl₂ molecules

The amount of H2 (g) present in a reaction mixture at equilibrium can be maximized by

increasing the temperature and decreasing the pressure by increasing the volume

Compared to the equilibrium vapor pressure of CH₃OH(l) at 300K, the equilibrium vapor pressure of C₂H₅OH(l) at 300K is

lower, because London dispersion forces among C₂H₅OH(l) molecules are greater than those among CH₃OH(l) molecules

HCHO₂(aq)+H₂O(l) ⇌ H₃O⁺(aq)+CHO₂⁻(aq) HCHO₂(aq), a weak acid (Ka=2x10⁻⁴), dissociates in water according to the equation above. Which of the following provides the best estimate of the pH of 0.5M HCHO₂ and identifies the species at the highest concentration (excluding H₂O) in the solution?

pH:2 Species at highest concentration: HCHO₂ (aq)

What is the value of the enthalpy change per mole of HCl(g) produced?

-93 kJ

Based on the thermodynamic data, which of the following is true at 298 K?

0<Keq<1

The pH of a solution made by combining 150mL of .10 M KOH with 50 mL of .2 M HBr is the closest to which of the following

12

A 0.0300 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 0.00500 mol of N₂O₄(g) is present at equilibrium?

12.5

N2O4(g)<-> 2NO2 Kp=3.0 at 70C colorless brown A mixture of NO2(g) and N2O4(g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above. If P(N2O4) is 1.33 atm when the system is at equilibrium at 70C which is P(NO2)?

2.0 atm

N2 (g) + 3H2 (g) = 2NH3 (g) H<0 NH3 (g) was synthesized at 200 C in the presence of a powdered Os (s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3 (g) in the mixture after equilibrium is reestablished?

Adding some N2 (g).

CaF₂⇌Ca²⁺+2F⁻ ∆H>0 Dissolution of the slightly soluble salt, CaF₂, is shown above. Which of the following changes will decrease [Ca²⁺] in a saturated solution of CaF₂ and why? (Assume that after each change some CaF₂ remains in contact with the solution.)

Adding some NaF because the reaction will proceed towards the reactants.

Which of thee following happens to H atoms in the forward reaction?

H atoms are both oxidized and reduced

A student prepares a solution by combining 100 mL of 0.30 M HNO3(aq) and 100 mL of 0,30 M KNO2(aq). Which of the following equations represents the reaction that best helps to explain why adding a few drops of 1.0 M HCl(aq) does not significantly change the pH of the solution?

H+(aq)+NO2-(aq)->HNO2(aq)

A 20. mL sample of 0.50 M HC₂H₃O₂ (aq) is titrated with 0.50 M NaOH. Which of the following best represents the species that react and the species produced in the reaction?

HC₂H₃O₂(aq)+OH --> H₂O(l)+C₂H₃O₂(aq)

Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?

HF, because its molecules form hydrogen bonds

CO (g) + 2H2 (g) = CH3OH (g) H<0 The synthesis of CH3OH (g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483K is 14.5. Which of the following explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased at 650K?

Kc will decrease because the reaction is exothermic.

Which of the following shows the relationship between K₁ and K₂ in the reactions represented above?

K₂=1/(K₁)²

CO (g) + 2H2 (g) = CH3OH (g) H<0 The synthesis of CH3OH (g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483K is 14.5. A mixture of CO (g) and H2 (g) is pumped into a previously evacuated 2.0 L reaction vessel. The total pressure of the system is 1.2 atm at equilibrium. What will be the total pressure of the system if the volume of the reaction vessel is reduced to 1.0 L at constant temperature?

Less than 1.2 atm

Which of the following best predicts how the partial pressures of the reacting species will be affected if a small amount of Ar(g) is added to the equilibrium mixture at constant volume?

No change will take place

N2O (g) + CO2 (g) = N2 (g) + CO2 (g) The rate of the reaction represented above increases significantly in the presence of P (s). Which of the following best explains this observation.

One of the reactants bind on the surface of P (s), which introduces an alternative reaction pathway with a lower activation energy.

The reaction between NO(g) and NO₃(g) is represented by the equation above. Which of the following orientations of collision between NO(g) and NO₃(g) is most likely to be effective?

Oxygen and Nitrogen atom going together

A 0.35g Sample of Li(s) is placed in an Erlenmeyer flask containing 100 mL of water at 25C. A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated. After all the Li(s) has reacted with H2O(l), the solution in the flask is added to a clean, dry buret, and used to titrate an aqueous solution of a monoprotic acid. The pH curve for this titration is shown in the diagram below. Which of the following changes will most likely increase the rate of reaction between Li(s) and water?

Using a 0.35g sample of Li(S) cut into small peices

A mixture of NO₂(g) and N₂O₄(g) is at equilibrium in a rigid reaction vessel. If the temperature of the mixture is decreased, then

[N₂O₄] will increase and the mixture will turn a lighter brown

The equation above represents an elementary step in a chemical reaction. Which of the following is the correct expression for the rate law of the elementary step?

r=k[NOBr]²

The temperature of the CH₃OH(l) is increased from 300K to 400K to vaporize all the liquid, which increases the pressure of the vessel to 0.3 atm. The experiment is repeated under identical conditions but this time using half the mass of CH₃OH that was used originally. What will be the pressure in the vessel at 400K?

0.15 atm

The value of Kp for the evaporation of CH₃OH(l) at 300K is closest to

0.2

On the basis of the information above, what is the approximate percent ionization of HNO₂ in a 1.0M HNO₂(aq) solution?

2.0%

(2 equations given with Keq) Equal volumes of 0.1 M AgNO3(aq) and 2.0 M NH3(aq) are mixed and the reactions represented above occur, which Ag species will have the highest concentration in the equilibrium system shown below and why? Ag⁺(aq)+2NH3(aq)<-> Ag(NH3)2⁺(aq) Keq3=?

Ag(NH3)2⁺(aq), because Keq3=1.6E7

(DIAGRAM) Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented above?

Hydrogen Bond

O3(g)+O(g)->2O2(g) The decomposition of O3(g) in the upper atmosphere is represented by the equation above. The potential energy diagram for the decomposition of O3(g) in the presence and absence of NO(g) is given below. (IMAGE) Which of the following mechanisms for the catalyzed reaction is consistent with the equation and diagram above.

O3(g)+NO(g)->NO2(g)+O2(g) slow NO2(g)+O(g)->NO(g)+O2(g) Fast

A student studied the kinetics of the reaction represented below by measuring the concentration of the reactant, X, over time. X->products The data are plotted in the graph below. Which of the following procedures will allow the student to determine the rate constant, k, for the reaction? (graph decreasing by decresing amount)

Plot ln[X] versus time and determine the magnitude of the slope

(Table shoes type of steel and characteristics) The table above provides some information about two types of steel, both of which are alloys of iron and carbon. Which of the following best helps to explain why high-carbon steel is more rigid than low carbon steel?

The additional carbon atoms within the allow make it more difficult for the iron atoms to slide past one another.

(TABLE) To determine the number of moles of Cu in the sample of the mixture, the students measured the absorbance of known concentrations of Cu(NO3)2(aq) using a spectrophotometer. A cuvette filled with some of the solution produced from the sample was also tested. The data recorded by one student are shown in the table above, on the basis of the data provided, which of the following is a possible error that the student made?

The student labelled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentrations