Thomas 2018 Chemistry MCQ

which of the following Lewis electron-dot diagram represents the molecule that is the most polar?

B. B-F

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

B. Low temperatures only

The masses of the carbon and hydrogen in samples of four pure hydrocarbons are given above. The hydrocarbon in which sample has the same empirical formula as propene, C3H6?

B. Sample B

The temperature of the CH3OH is increased from 300K to 400K to vaporize all the liquid, which increases the pressure on the vessel to 0.30atm. The experiment is repeated under identical conditions but this time using half the mass of CH3OH that was use originally. What will be the pressure in the vessel at 400K?

A. 0.15 atm

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

A. PCl5(g) <-> PCl3(g) + Cl2(g)

AgNO3(aq) + NaCl(aq) -> AgCl(s) +NaNO3(aq) In an experiment a student mixes a 50.0 mL sample of 0.100M AgNO3(aq) with a 50.0mL sample of 0.100 NaCl(aq) at 20 degrees Celsius in a coffee-cup calorimeter. Which of the following is the enthalpy change of the precipitation reaction represented above if the final temperature of the mixture is 21.0 degrees Celsius? (Assume that the total mass of the mixture is 100g and that the specific heat capacity of the mixture is 4.2 J/(gC)

A. -84 Kj/mol (q=mcdeltaT)

When a small amount of 12 M HNO3(aq) is added to a buffer solution made by mixing CH3NH2(aq) and the CH3NH3Cl(aq), 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(aq) is added?

A. CH3NH2(aq) + H+(aq) <-> CH3NH3+(aq)

The Maxwell-Boltzmann distributions of molecular speeds in the samples of two different gases at the same temperature are shown above. Which gas has the greater molar mass?

A. Gas A

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

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

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

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

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

C. K2 = 1/(k1)^2

Equimolar samples of each of the three gases, H2(g), I2(g), and HI(g), are introduced into a 3.o L container that is heated to 600 degrees Celsius. According to the information above, which of the following will occur as the system approaches equilibrium?

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

The rate of reaction increases significantly in the presence of Pd(s). Which of the following best explains this observation?

C. One of the reactants binds on the surface of Pd, which introduces an alternative reaction pathway with a lower activation energy.

"2NOBr(g) -> 2NO(g)+Br2(g)" 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?

C. Rate = k[NOBr]^2

Based on the Coulomb's Law and the information in the table above, which of the following anions is most likely to have the strongest interactions with nearby water molecules in an aqueous solution?

C. S^2-

Equimolar samples of Pb(OH)2(s), PbI2(s), and PbF2(s) are placed in three separate beakers, each containing 250mL of water at 25 degrees Celsius. 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 above, a solution of which compounds will have the lowest [Pb2+]?

A. Pb(OH)2(s)

A student studied the kinetics of the reaction represented above by measuring the concentration of reactant, X, over time. Which of the following procedures will allow the student to determine the rate constant, K, for the reaction?

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

A balloon filled with 0.25 mol of He(g) at 273K and 1 atm is allowed to rise through the atmosphere. Which of the following explains what happens to the volume of the balloon as it rises from the ground level to an altitude where the air temperature is 220K and the air pressure is 0.1 atm?

A. The volume will increase because the decrease in air pressure will have a greater effect than the decrease in the temperature.

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

B. increasing the temperature and decreasing the pressure by increasing the volume.

The pH of a solution made by combining 150mL of 0.10 M KOH(aq) with 50mL of 0.20M HBr(aq) is closest to which of the following?

B.4

The mass of the Cu(s) produced in step 3 was slightly more than the mass predicted from the 3.8g of Cu3(PO4)2(s) recovered from step 1. Which of the following could account for the discrepancy in the yield of Cu(s) from step 3?

C. Some unreacted Zn(s) was mixed in the with the Cu(s).

What can be concluded regarding the strength of the C-H, N-H, and O-H bonds in the molecules shown?

C. The O-H bond is the strongest.

The ionization energies of an unknown element, X are listed in the table above. Which of the following is most likely empirical formula of a compound formed from element X and phosphorus, P?

C. X3P2

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

C. are attracted to the sides of the container and strike the container walls with more force than expected

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

C. lower, because LDF among C2H5OH molecules are greater than those among CH3OH molecules.

The reaction between NO(g) and NO3(g) is represented by NO(g)+ NO3(g) -> 2NO2(g). Which of the following orientations of collisions between NO(g) and NO3(g) is most likely to be effective?

D.

Which of the following particle diagrams best represents the products when four molecules of H2O2(l) decompose into water and oxygen gas at room temperature?

D. Diagram with 4 water molecules and 2 pairs of oxygen molecules

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

D. Propanoic acid, because it can form intermolecular hydrogen bonds

The step-wise dissociation of selenous acid, H2SeO3(aq), is represented by the equation above. Which of the following best helps explain why the value of Ka@ is so much smaller than the value of Ka>

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

A 50g sample of Fe at 100 degrees Celsius to 500mL of water at 35 degrees Celsius in a perfectly insulated container. Which of the following statements is true?

D. The heat energy lost by the Fe will be equal to the heat energy gained by the water.

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 degrees Celsius?

C. the reaction has a high activation energy.

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

D.

Based of the values of deltaG for the three reactions represented above, what is the value of deltaG for the reaction represented below?

D. -1320 kj/mol

A 0.0300 mol sample of NO2(g) is placed in a rigid 1L 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 N204(g) is present at equilibrium?

D. 12.5

"HNO2 <-> H(aq) + NO2(aq), Ka = 4.0x10^-4" On the basis of the information above, what is the approximate percent ionization of HNO2 in a 1.0 M HNO2 (aq) solution?

D. 2.0%

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

D. A physical change takes place because intermolecular attractions are overcome.

CaF2(s) <-> Ca2+(aq) + 2F-(aq) deltaH > 0 Dissolution of the slightly soluble salt CaF2 is shown by the equation above. Which of the following changes will decrease [Ca2+] in a saturated solution of CaF2, and why? (Assume that after each change some CaF2(s) remains in contact with the solution.)

D. Adding NaF(s), because the reaction will proceed towards reactants

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?

D. The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does.

HCHO2(aq) + H2O <-> H3O+(aq) + CHO2-(aq) HCHHO2(aq), is 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 0.5 M HCHO2(aq) and identifies the species at the highest concentration (excluding the H20) in the solution?

D. pH 2 / Species at highest Concentration HCHO2(aq)

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

D. Network Covalent/Metallic/Ionic

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.

D. PO4^3-(aq)

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

D. Spectrophotometry

Which of the following best helps to explain why CCl4 us a liquid whereas Cl4 is a solid when both are at 25 degrees Celsius?

D. The LDF are stronger in Cl4 because Cl4 has a more polarizable electron cloud than CCl4.

When 70 g of Li3(s) (molar mass 35 g/mol) reacts with excess H2(g), 8g of LiH(s) is produced. The percent yield is closest to...

B. 25%

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

B. 0.2

If 3.8g of Cu3(PO4)2(s) was recovered from step 1, what was the approximate [Cu2+] in the original solution? (The molar mass of Cu3(PO4)2 is 381 g/mol.)

B. 0.30 M

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

C. HC2H3O2(aq) + OH(aq) -> C2H3O2 (aq) + H2O(l)

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

C. H atoms are both oxidized and reduced.

Equal volumes of solutions in two different vessels are represented above. If the solution represented in vessel 1 is KCl(aq), then the solution represented in vessel 2 could be an aqueous solution of..

D. CaCl2 with twice the molarity of the solution in vessel 1

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

D. E = +0.02V (-0.74)-(0.76)