Chemistry Quiz Wednesday

A mixture of H2(g) and O2(g) is placed in a container as represented above. The H2(g) and O(g) 2 react to form H2O(g). Which of the following best represents the container after the reaction has gone to completion?

B

After a certain pesticide compound is applied to crops, its decomposition is a first-order reaction with a half-life of 56 days. What is the rate constant, k, for the decomposition reaction? (A) 0.012 day−1 (B) 0.018 day−1 (C) 56 day−1 (D) 81 day−1

(A) 0.012 day−1

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? (A) 0.40 M 0.40 M 0.20 M (B) 0.30 M 0.30 M 0.90 M (C) 0.15 M 0.15 M 0.30 M (D) 0.10 M 0.10 M 0.20 M

(A) 0.40 M 0.40 M 0.20 M

The value of the equilibrium constant for the reaction represented above is 1 × 10^10. What is the value of the equilibrium constant for the following reaction? 2 GeCl4(g) ---> 2 Ge(g) + 4 Cl2(g) (A) 1 × 10^-20 (B) 1 × 10^-10 (C) 1 × 10^10 (D) 1 × 10^20

(A) 1 × 10^-20

Which compound, chloroacetic acid or iodoacetic acid, most likely has the lower boiling point, and why? (A) Chloroacetic acid, because the London dispersion forces among its molecules are weaker. (B) Chloroacetic acid, because the dipole-dipole forces among its molecules are weaker. (C) Iodoacetic acid, because the London dispersion forces among its molecules are stronger. (D) Iodoacetic acid, because the dipole-dipole forces among its molecules are stronger.

(A) Chloroacetic acid, because the London dispersion forces among its molecules are weaker.

Which of the following statements is true about sodium glycinate, represented above? (A) It is an ionic solid at room temperature. (B) It is not soluble in water. (C) It evaporates easily because of the lack of hydrogen bonding. (D) It dissolves in water to form an acidic solution.

(A) It is an ionic solid at room temperature.

A mixture of two gases, 0.01 mol of C4H10(g) and 0.065 mol of O2(g), is pumped into a cylinder with a movable piston, as shown above. The mixture, originally at 200qC and 1.0 atm, is sparked and the reaction represented below occurs. 2 C4H10(g) + 13 O2(g) --> 8 CO2(g) + 10 H2O(g) Which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (A) The piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules. (B) The position of the piston will be unchanged, because the total mass of the gases in the cylinder does not change. (C) The position of the piston will be unchanged, because the temperature and pressure of the contents of the cylinder remain the same. (D) The piston will be lower than its original position, because the product molecules are smaller than the reactant molecules.

(A) The piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules.

The concentration of F(aq) in drinking water that is considered to be ideal for promoting dental health is 4.0 x 105 M. Based on the information above, the maximum concentration of Ca2+(aq) that can be present in drinking water without lowering the concentration of F(aq) below the ideal level is closest to (A) 0.25 M (B) 0.025 M (C) 1.6 x 10^-6 M (D) 1.6 x 10^-15 M

(B) 0.025 M

Of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why? (A) 0.1 M HC2H3O2(aq) because its molecules have the most atoms. (B) 0.1 M KI(aq)because KI completely dissociates in water to produce ions. (C) 0.1 M CH3OH(aq) because its molecules can form hydrogen bonds. (D) All three solutions have the same electrical conductivity because the concentrations are the same.

(B) 0.1 M KI(aq)because KI completely dissociates in water to produce ions.

Which of the following equations best represents the species that react and the species that are produced when CaCO3(s) and HCl(aq) are combined? (A) 2 H+(aq) + CaCO3(s) --> Ca2+(aq) + CO3 2(aq) + H2(g) (B) 2 H+(aq) + CaCO3(s) --> Ca2+(aq) + H2O(l) + CO2(g) (C) 2 H+(aq) + CaCO3(s) --> Ca2+(aq) + 2 OH (aq) + CO(g) (D) 2 HCl(aq) + CaCO3(s) --> Ca2+(aq) + H2O(l) + CO2(g) + 2 Cl(aq)

(B) 2 H+(aq) + CaCO3(s) --> Ca2+(aq) + H2O(l) + CO2(g)

The value of K w at 40°C is 3.0 x 10^-14. What is the pH of pure water at 40C? (A) 3.0 (B) 6.8 (C) 7.0 (D) 7.2

(B) 6.8

The first five ionization energies of an unknown element are listed in the table above. Which of the following statements correctly identifies the element and cites the evidence supporting the identification? (A) Na, because of the large difference between the first and the second ionization energies (B) Al, because of the large difference between the third and fourth ionization energies (C) Si, because the fifth ionization energy has the greatest value (D) P, because a neutral atom of P has five valence electrons

(B) Al, because of the large difference between the third and fourth ionization energies

Which of the following is true about the geometry of the glycinium cation? (A) The leftmost C atom and all the atoms directly bonded to it lie in the same plane. (B) Both C atoms and both O atoms lie in the same plane. (C) The NCC bond angle is 180°. (D) The geometry around the N atom is planar.

(B) Both C atoms and both O atoms lie in the same plane.

The photoelectron spectra for H and He are represented above. Which of the following statements best accounts for the fact that the peak on the He spectrum is farther to the left and higher than the peak on the H spectrum? (A) He has an additional valence electron in a higher energy level than the valence electron in H. (B) He has a greater nuclear charge than H and an additional electron in the same energy level. (C) He has a completely filled valence shell in which the electrons are a greater distance from the nucleus than the distance between the H nucleus and its electron. (D) It takes longer for the electrons in He to be removed due to the higher nuclear mass of He.

(B) He has a greater nuclear charge than H and an additional electron in the same energy level.

A solution is prepared by mixing equal volumes of 0.20 M HC2H3O2 and 0.40 M NaC2H3O2 . Which of the following correctly describes what occurs if a small amount of HCl(aq) or NaOH(aq) is added? (A) If HCl(aq) is added, the pH will increase only slightly because the Cl− ions will react with C2H3O2− ions. (B) If HCl(aq) is added, the pH will decrease only slightly because the H+ ions will react with C2H3O2− ions. (C) If NaOH(aq) is added, the pH will increase only slightly because the OH− ions will react with C2H3O2− ions. (D) If NaOH(aq) is added, the pH will decrease only slightly because the OH− ions will react with HC2H3O2 molecules.

(B) If HCl(aq) is added, the pH will decrease only slightly because the H+ ions will react with C2H3O2− ions.

The data from a study of the decomposition of NO2(g) to form NO(g) and O2(g) are given in the table above. Which of the following rate laws is consistent with the data? (A) Rate = k [NO2] (B) Rate = k [NO2]2 (C) Rate = k 1/[NO2]^2 (D) Rate = k 1/[NO2]

(B) Rate = k [NO2]2

Which of the following can be inferred from the diagram above that shows the dependence of potential energy on the internuclear distance between two atoms? (A) The atoms form a bond with a bond length of 25 pm. (B) The atoms form a bond with a bond length of 75 pm. (C) The net force between the atoms is attractive at 25 pm. (D) The net force between the atoms is attractive at 75 pm.

(B) The atoms form a bond with a bond length of 75 pm.

A sealed 10.0 L flask at 400 K contains equimolar amounts of ethane and propanol in gaseous form. Which of the following statements concerning the average molecular speed of ethane and propanol is true? (A) The average molecular speed of ethane is less than the average molecular speed of propanol. (B) The average molecular speed of ethane is greater than the average molecular speed of propanol. (C) The average molecular speed of ethane is equal to the average molecular speed of propanol. (D) The average molecular speeds of ethane and propanol cannot be compared without knowing the total pressure of the gas mixture.

(B) The average molecular speed of ethane is greater than the average molecular speed of propanol.

The diagram above represents a particle in aqueous solution. Which of the following statements about the particle is correct? (A) The particle must be a cation because the negative end of each water molecule is pointed toward it. (B) The particle must be an anion because the positive end of each water molecule is pointed toward it. (C) The charge of the particle cannot be determined because water molecules have no net charge. (D) The charge of the particle cannot be determined because the water molecules are arranged symmetrically and their partial charges cancel.

(B) The particle must be an anion because the positive end of each water molecule is pointed toward it.

An aqueous solution contains small but equal concentrations of both chloroacetic and fluoroacetic acids. Which statement comparing the percent ionizations of the two acids in the solution is true? (A) The percent ionization of chloroacetic acid is greater than that of fluoroacetic acid. (B) The percent ionization of chloroacetic acid is less than that of fluoroacetic acid. (C) The percent ionizations cannot be compared without knowing the concentrations of thetwo acids. (D) The percent ionizations cannot be compared without knowing the pH of the solution.

(B) The percent ionization of chloroacetic acid is less than that of fluoroacetic acid.

The reaction represented above occurs when 2.00 × 10-4 mol of pure acetylsalicylic acid, C9H8O4 , is completely dissolved in 15.00 mL of water in a flask and titrated to the equivalence point with 0.100 M NaOH(aq). Which of the following statements about the titration is true at the equivalence point? (A) [C9H8O4] is greater than [C9H7O4]. (B) [C9H8O4] is less than [C9H7O4 ]. (C) [C9H8O4] is equal to [C9H7O4]. (D) The relationship between [C9H8O4] and [C9H7O4] cannot be determined without additional information.

(B) [C9H8O4] is less than [C9H7O4 ].

To catalyze a biochemical reaction, an enzyme typically (A) drives the reaction to completion by consuming byproducts of the reaction (B) binds temporarily to reactant molecules to lower the activation energy of the reaction (C) dissociates into additional reactant molecules, thereby increasing the reaction rate (D) decomposes and releases energy to increase the number of successful collisions between reactant molecules

(B) binds temporarily to reactant molecules to lower the activation energy of the reaction

What is the value of E° for the cell? (A) 0.04 V (B) 0.84 V (C) 1.56 V (D) 2.36 V

(C) 1.56 V

What is the approximate HOC bond angle in the glycinium cation? (A) 180° (B) 120° (C) 105° (D) 90°

(C) 105°

At 25qC, enough distilled water is added to a 30.0 mL sample of HNO3(aq) with a pH of 4.20 so that the final pH of the diluted solution is 5.20. The volume of distilled water added to the original solution is closest to (A) 30.0 mL (B) 60.0 mL (C) 270. mL (D) 300. mL

(C) 270. mL

A student titrates 10.0 mL samples of 1.0 M solutions of each of the haloacetic acids with a standard solution of NaOH. Which of the following statements correctly predicts the volume of NaOH(aq) needed to reach the equivalence point? (A) Fluoroacetic acid will need the smallest volume of NaOH(aq) to reach the equivalence point. (B) Iodoacetic acid will need the smallest volume of NaOH(aq) to reach the equivalence point. (C) All of the acids will need the same volume of NaOH(aq) to reach the equivalence point. (D) All of the haloacetic acids are weak; therefore none will reach an equivalence point.

(C) All of the acids will need the same volume of NaOH(aq) to reach the equivalence point.

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) ? (A) Mass of KCl(s), initial temperature of the water, and final temperature of the solution (B) Mass of H2O, initial temperature of the water, and final temperature of the solution (C) Mass of KCl(s), mass of H2O, initial temperature of the water, and final temperature of the solution (D) Mass of KCl(s), mass of H2O, initial temperature of the water, final temperature of the solution, and atmospheric pressure

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

Samples of NaF(s) and NH4Cl(s) are dissolved in separate beakers that each contain 100 mL of water. One of the salts produces a slightly acidic solution. Which of the following equations best represents the formation of the slightly acidic solution? (A) Na +(aq) + 2 H2O(l) --> NaOH(aq) + H3O+(aq) (B) F −(aq) + H2O(l) --> HF(aq) + OH−(aq) (C) NH4+(aq) + H2O(l) --> NH3(aq) + H3O+(aq) (D) Cl (aq) + H2O(l) --> HCl(aq) + OH−(aq)

(C) NH4+(aq) + H2O(l) --> NH3(aq) + H3O+(aq)

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? (A) The rates of both the forward and reverse reactions decrease. (B) The rates of both the forward and reverse reactions do not change. (C) The rate of the forward reaction becomes greater than the rate of the reverse reaction. (D) The rate of the forward reaction becomes less than the rate of the reverse reaction.

(C) The rate of the forward reaction becomes greater than the rate of the reverse reaction.

Which of the following best explains why the reaction represented above is not observed to occur at room temperature? (A) The rate of the reaction is extremely slow because of the relatively small value of 'Gq for the reaction. (B) The entropy of the system decreases because the carbon atoms in graphite are less ordered than those in diamond. (C) The reaction has an extremely large activation energy due to strong three-dimensional bonding among carbon atoms in diamond. (D) The reaction does not occur because it is not thermodynamically favorable.

(C) The reaction has an extremely large activation energy due to strong three-dimensional bonding among carbon atoms in diamond.

Solid carbon tetrachloride, CCl4(s), is represented by the diagram above. The attractions between the CCl4 molecules that hold the molecules together in the solid state are best identified as (A) polar covalent bonds (B) nonpolar covalent bonds (C) intermolecular attractions resulting from temporary dipoles (D) intermolecular attractions resulting from permanent dipoles

(C) intermolecular attractions resulting from temporary dipoles

In an experiment, 30.0 g of ethane and 30.0 g of propanol are placed in separate reaction vessels. Each compound undergoes complete combustion with excess O2(g). Which of the following best compares the quantity of heat released in each combustion reaction? (A) qethane < qpropanol (B) qethane = qpropanol (C) qethane > qpropanol (D) The quantities of heat released in the combustions of ethane and propanol cannot be compared without knowing the specific heat capacity of the compounds.

(C) qethane > qpropanol

The formation of Fe(s) and O2(g) from FeO(s) is not thermodynamically favorable at room temperature. In an effort to make the process favorable, C(s) is added to the FeO(s) at elevated temperatures. Based on the information above, which of the following gives the value of K eq and the sign of 'G° for the reaction represented by the equation below at 1000 K? 2 FeO(s) + C(s) ---> 2 Fe(s) + CO2(g) (A) 1 x 10^-38 Positive (B) 1 x 10^-38 Negative (C) 1 x 10^26 Positive (D) 1 x 10^26 Negative

(D) 1 x 10^26 Negative

Another sample of eggshell reacts completely with 4.0 mL of an HCl(aq) solution of unknown concentration. If the reaction produced 0.095 atm of gas, the concentration of the HCl(aq) solution was at least (A) 0.0020 M (B) 0.050 M (C) 0.50 M (D) 1.0 M

(D) 1.0 M

Which of the following is the net ionic equation for the overall reaction that occurs as the cell operates? (A) Ag(s) + Zn2+(aq) --> Ag2+(aq) + Zn(s) (B) Ag+(aq) + Zn2+(aq) + 3 e --> AgZn(s) (C) Ag+(aq) + Zn(s) --> Ag(s) + Zn2+(aq) + e (D) 2 Ag+(aq) + Zn(s) --> 2 Ag(s) + Zn2+(aq)

(D) 2 Ag+(aq) + Zn(s) --> 2 Ag(s) + Zn2+(aq)

The mass percent of CaCO3(s) in the eggshell sample is closest to (A) 30% (B) 45% (C) 60% (D) 75%

(D) 75%

In a one-person spacecraft, an astronaut exhales 880 g of CO2(g) (molar mass 44 g/mol) per day. To prevent the buildup of CO2(g) in the spacecraft, a device containing LiOH(s) is used to remove the CO2(g), as represented by the equation above. What mass of LiOH(s) (molar mass 24 g/mol) is needed to react with all of the CO2(g) produced by an astronaut in one day? (A) 40. g (B) 240 g (C) 480 g (D) 960 g

(D) 960 g

The saturated CuSO4(aq) shown above is left uncovered on a lab bench at a constant temperature. As the solution evaporates, 1.0 mL samples of the solution are removed every three days and the [SO42] in the samples is measured. It is observed that the [SO42] in the solution did not change over time. Which of the following best helps to explain the observation? (A) As the solution evaporates, Cu2+(aq) and SO42(aq) leave the beaker along with the water molecules. (B) As the solution evaporates, the dissolution of CuSO4(s) in the beaker decreases. (C) The evaporation of water is endothermic, so more CuSO4(s) dissolves exothermically in the solution, which increases the [SO42]. (D) As water evaporates, more CuSO4(s) precipitates out of the solution in the beaker

(D) As water evaporates, more CuSO4(s) precipitates out of the solution in the beaker

Which of the following is the molecular formula of the unknown compound? (A) C4H8 (B) C4H8O (C) C4H4O2 (D) C4H8O2

(D) C4H8O2

In which of the following processes will S° be negative? (A) C2H5OH(l) --> C2H5OH(g) (B) NaCl(s) --> NaCl(l) (C) CO2(s) --> CO2(g) (D) Cl(g) --> Cl2(l)

(D) Cl(g) --> Cl2(l)

As a sample of KNO3(s) is stirred into water at 25°C, the compound dissolves endothermically. Which of the following best helps to explain why the process is thermodynamically favorable at 25°C? (A) All endothermic processes are thermodynamically favorable. (B) Stirring the solution during dissolution adds the energy needed to drive an endothermic process. (C) Dissolving the salt decreases the enthalpy of the system. (D) Dissolving the salt increases the entropy of the system.

(D) Dissolving the salt increases the entropy of the system.

A student obtains a mixture of the liquids hexane and octane, which are miscible in all proportions. Which of the following techniques would be best for separating the two components of the mixture, and why? (A) Filtration, because the different densities of the liquids would allow one to pass through the filter paper while the other would not. (B) Paper chromatography, because the liquids would move along the stationary phase at different rates owing to the difference in polarity of their molecules. (C) Column chromatography, because the higher molar mass of octane would cause it to move down the column faster than hexane. (D) Distillation, because the liquids would boil at different temperatures owing to the difference in strength of their intermolecular forces.

(D) Distillation, because the liquids would boil at different temperatures owing to the difference in strength of their intermolecular forces.

A student observes that the equilibrium constant for a reaction is greater than 1.0 at temperatures below 500 K but less than 1.0 at temperatures above 500 K. What can the student conclude about the values of DH and DS for the reaction? (A) H>0 and S>0 (B) H>0 and S<0 (C) H<0 and S>0 (D) H<0 and S<0

(D) H<0 and S<0

Based on the structural formulas, which of the following identifies the compound that is more soluble in water and best helps to explain why? (A) Ethane, because the electron clouds of its molecules are more polarizable than those of propanol. (B) Ethane, because its molecules can fit into the spaces between water molecules more easily than those of propanol can. (C) Propanol, because its molecules have a greater mass than the molecules of ethane have. (D) Propanol, because its molecules can form hydrogen bonds with water molecules but those of ethane cannot.

(D) Propanol, because its molecules can form hydrogen bonds with water molecules but those of ethane cannot.

Which of the following best explains why the combustion reactions represented in the table are exothermic? (A) The number of bonds in the reactant molecules is greater than the number of bonds in the product molecules. (B) The number of bonds in the reactant molecules is less than the number of bonds in the product molecules. (C) The energy required to break the bonds in the reactants is greater than the energy released in forming the bonds in the products. (D) The energy required to break the bonds in the reactants is less than the energy released in forming the bonds in the products.

(D) The energy required to break the bonds in the reactants is less than the energy released in forming the bonds in the products.

Which of the following best helps to explain why Na(s) is more reactive with water than Mg(s) is? (A) Na(s) is softer than Mg(s). (B) The atomic mass of Na is less than that of Mg. (C) The Na+ ion has weaker Coulombic attraction to an anion than the Mg 2+ ion has. (D) The first ionization energy of Na is less than that of Mg.

(D) The first ionization energy of Na is less than that of Mg.

The structural formulas for two isomers of 1,2-dichloroethene are shown above. Which of the two liquids has the higher equilibrium vapor pressure at 20qC, and why? (A) The cis-isomer, because it has dipole-dipole interactions, whereas the trans-isomer has only London dispersion forces (B) The cis-isomer, because it has only London dispersion forces, whereas the trans-isomer also has dipole-dipole interactions (C) The trans-isomer, because it has dipole-dipole interactions, whereas the cis-isomer has only London dispersion forces (D) The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

(D) The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

Which of the following modifications will increase the rate of the reaction the most? (A) Using 2.0 M CH3COOH(aq) instead of 2.0 M HCl(aq) (B) Cooling the HCl(aq) to a lower temperature than it was in the original experiment (C) Reducing the volume of the reaction vessel (D) Using eggshells that are more finely powdered than those used in the original experiment

(D) Using eggshells that are more finely powdered than those used in the original experiment

A 1.0 mol sample of He(g) at 25°C is mixed with a 1.0 mol 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? (A) Will increase Will increase (B) Will increase Will decrease (C) Will decrease Will increase (D) Will decrease Will decrease

(D) Will decrease Will decrease

Of the following diagrams, which best represents the structure of solid KF ?

B) The completely dispersed one.