AP chemistry Midterm MCQ

How many moles of Na+Na+ ions are in 100.mL100.mL of 0.100MNa3PO4(aq)0.100MNa3PO4(aq) ?

0.0300mol

A student uses visible spectrophotometry to determine the concentration of CoCl2(aq)CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq)CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. Question The original solution used to make the solutions for the standard curve was prepared by dissolving 2.60g2.60g of CoCl2CoCl2 (molar mass 130.g/mol130.g/mol) in enough water to make 100.mL100.mL of solution. What is the molar concentration of the solution? Responses

0.200M

How many grams of CaCl2CaCl2 (molar mass =111g/mol=111g/mol) are needed to prepare 100.mL100.mL of 0.100MCl−(aq)0.100MCl−(aq) ions?

0.555g

Which of the following is the ground-state electron configuration of the F−F− ion?

1s2 2s2 2p6

Which of the following ground-state electron configurations represents the atom that has the lowest first-ionization energy?

1s2 2s2 2p6 3s1

The complete photoelectron spectrum of an element is given above. Which of the following electron configurations is consistent with the spectrum?

1s2 2s2 2p6 3s2 3p3

Which of the following best represents the ground-state electron configuration for an atom of selenium?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4

Al(s)→Al3+(aq)+3e−Al(s)→Al3+(aq)+3e− Zn2+(aq)+2e−→Zn(s)Zn2+(aq)+2e−→Zn(s) The half-reactions for the oxidation-reduction reaction between Al(s)Al(s) and Zn2+(aq)Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s)Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients?

2

Which of the following numerical expressions gives the number of particles in 2.0g2.0g of NeNe?

2.0g/20.18g/mol(6.0×1023particles/mol)

An equimolar mixture of N2(g)N2(g) and Ar(g)Ar(g) is kept inside a rigid container at a constant temperature of 300 KK. The initial partial pressure of ArAr in the mixture is 0.75atm0.75atm. An additional amount of ArAr was added to the container, enough to double the number of moles of ArAr gas in the mixture. Assuming ideal behavior, what is the final pressure of the gas mixture after the addition of the ArAr gas?

2.25atm2.25atm, because doubling the number of moles of ArAr doubles its partial pressure.

Ni(s)→Ni2+(aq)+2e−Ni(s)→Ni2+(aq)+2e− Ag+(aq)+e−→Ag(s)Ag+(aq)+e−→Ag(s) Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag+(aq)Ag+(aq) and Ni(s)Ni(s) based on the half-reactions represented above?

2Ag+(aq)+Ni(s)→2Ag(s)+Ni2+(aq)

NO(g)NO(g) and O2(g)O2(g) react to form NO2(g)NO2(g). The rate law of the reaction is rate=k[NO]2[O2]rate=k[NO]2[O2]. If the reaction occurs in a single elementary step that is a three-body molecular collision, then which of the following is the equation for the elementary step?

2NO+O2→2NO2

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the proposed mechanism, what is the balanced chemical equation for the overall reaction?

2O3(g)→3O2(g)

A sample of carbonate rock is a mixture of CaCO3CaCO3 and MgCO3MgCO3. The rock is analyzed in a laboratory, and the results are recorded in the table above. Which columns in the table provide all the information necessary to determine the mole ratio of CaCa to MgMg in the rock?

3, 4, 6, 7

A student uses visible spectrophotometry to determine the concentration of CoCl2(aq)CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq)CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. Question A wavelength of 510nm510nm corresponds to an approximate frequency of 6×1014s−16×1014s−1. What is the approximate energy of one photon of this light? Responses

4×10−19J

The diagram above represents the photoelectric effect for a metal. When the metal surface is exposed to light with increasing frequency and energy of photons, electrons first begin to be ejected from the metal when the energy of the photons is 3.3×10−19J3.3×10−19J. Question Which of the following is closest to the frequency of the light with photon energy of 3.3×10−19J3.3×10−19J?

5.0×1014s−1

A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?

A cube of metal was changed into a flat sheet of metal.

A gas mixture at 0°C0°C and 1.0atm1.0atm contains 0.010mol0.010mol of H2H2, 0.015mol0.015mol of O2O2, and 0.025mol0.025mol of N2N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2)(H2) in the mixture? Responses

About 0.20atm0.20atm, because H2H2 comprises 20%20% of the total number of moles of gas.

A student mixes 20.0g20.0g of white KClKCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?

After the water has evaporated, the white crystals in the beaker have a mass of 20.0g20.0g.

When the chemical reaction 2NO(g)+O2(g)→2NO2(g)2NO(g)+O2(g)→2NO2(g) is carried out under certain conditions, the rate of disappearance of NO(g)NO(g) is 5.0×10−5 Ms−15.0×10−5 Ms−1. What is the rate of disappearance of O2(g)O2(g) under the same conditions?

Because two molecules of NONO are consumed per molecule of O2O2, the rate of disappearance of O2(g)O2(g) is 2.5×10−5 Ms−12.5×10−5 Ms−1.

The structure of one form of boron nitride is represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

If NaNa reacts with chlorine to form NaClNaCl, which of the following elements reacts with NaNa to form an ionic compound in a one-to-one ratio, and why?

BrBr, because it has the same number of valence electrons as ClCl.

The initial rate of formation of CO2(g)CO2(g) from the chemical reaction represented by the equation above was studied in two separate experiments. The table above provides the experimental conditions used. If both experiments are carried out with finely powdered samples of the solid and 50.0mL50.0mL of HCl(aq)HCl(aq), which experiment, if any, will have the faster initial rate of formation of CO2(g)CO2(g) and why?

CO2(g)CO2(g) will be formed at a faster rate in experiment 2 because more H+H+ particles can react per unit time.

RbClRbCl has a high boiling point. Which of the following compounds is also likely to have a high boiling point, and why?

CsClCsCl, because its elements have very different electronegativities and it is an ionic compound.

The ionic compounds NaClNaCl and MgSMgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why?

Diagram 1 represents NaClNaCl; it has a lower melting point than MgSMgS because the coulombic attractions between its singly charged Na+Na+ ions and the Cl−Cl− ions are weaker than those between the ions in MgSMgS.

The survival of aquatic organisms depends on the small amount of O2O2 that dissolves in H2OH2O. The diagrams above represent possible models to explain this phenomenon. Which diagram provides the better particle representation for the solubility of O2O2 in H2OH2O, and why?

Diagram 2, because the polar H2OH2O molecules can induce temporary dipoles on the electron clouds of O2O2 molecules.

Which graph best represents the changes in concentration of O2(g)O2(g), and why

Graph 1, because the rate of O2O2 consumption is half the rate at which NONO is consumed; two molecules of NONO react for each molecule of O2O2 that reacts.

A student places a piece of I2(s)I2(s) in 50.0 mL50.0 mL of H2O(l)H2O(l), another piece of I2(s)I2(s) of the same mass in 50.0 mL 50.0 mL of C6H14(l)C6H14(l), and shakes the mixtures. The results are shown above. What do the results indicate about the intermolecular interactions of the substances?

I2I2 and C6H14C6H14 have similar intermolecular interactions, and I2I2 and H2OH2O do not.

BrBr, because it has the same number of valence electrons as ClCl.If NaNa reacts with chlorine to form NaClNaCl, which of the following elements reacts with NaNa to form an ionic compound in a one-to-one ratio, and why?

If NaNa reacts with chlorine to form NaClNaCl, which of the following elements reacts with NaNa to form an ionic compound in a one-to-one ratio, and why?

The complete photoelectron spectrum for an element is shown above. Which of the following observations would provide evidence that the spectrum is consistent with the atomic model of the element?

In its compounds, the element tends to form ions with a charge of +1+1.

The diagram above shows two resonance structures for a molecule of C6H6C6H6. The phenomenon shown in the diagram best supports which of the following claims about the bonding in C6H6C6H6 ?

In the C6H6C6H6 molecule, all the bonds between the carbon atoms have the same length.

A student has a 1g1g sample of each of the following compounds: NaClNaCl, KBrKBr, and KClKCl. Which of the following lists the samples in order of increasing number of moles in the sample?

KBr<KCl<NaCl

The electron cloud of HFHF is smaller than that of F2F2 , however, HFHF has a much higher boiling point than F2F2 has. Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HFHF?

Liquid F2F2 has weak dispersion force attractions between its molecules, whereas liquid HFHF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.

The table above summarizes data given to a student to evaluate the type of change that took place when substance XX was mixed with water. The student claimed that the data did not provide enough evidence to determine whether a chemical or physical change took place and that additional tests were needed. Which of the following identifies the best way to gather evidence to support the type of change that occurred when water and XX were mixed?

Measuring the electrical conductivities of XX and the mixture of water and X

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 26amu26amu represents an isotope of which of the following elements?

MgMg with 14 neutrons

Which statement correctly compares what occurs when molecules absorb photons in the microwave region with what occurs when molecules absorb photons in the infrared region?

Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states.

Which of the following elements has the mass spectrum represented above?

Mo

Equal volumes of 0.2M0.2⁢M solutions of lead(II)(II) nitrate and potassium bromide are combined to form lead(II)(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

Pb2+(aq)+2Br−(aq)→PbBr2(s)

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)H2(g)⁢+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)HI(g)⁢+ICl(g)→HCl(g)+I2(g)(fast) Which of the following represents a rate law for the overall reaction that is consistent with the proposed mechanism?

Rate=k[H2][ICl]

2HBr(g)+O2(g)→H2O2(g)+Br2(g)2HBr(g)+O2(g)→H2O2(g)+Br2(g) Based on a kinetics study of the reaction represented by the equation above, the following mechanism for the reaction is proposed. Step 1:HBr(g)+O2(g)→HO2Br(g)HBr(g)+O2(g)→HO2Br(g)(slow)Step 2:HO2Br(g)+HBr(g)→2HOBr(g)HO2Br(g)+HBr(g)→2HOBr(g)(fast)Step 3:2HOBr(g)→H2O2(g)+Br2(g)2⁢HOBr(g)→H2O2(g)+Br2(g)(fast) Which of following rate laws is consistent with the proposed mechanism?

Rate=k[HBr][O2]

2HO2(g)→H2O2(g)+O2(g)2HO2(g)→H2O2(g)+O2(g) The reaction represented by the chemical equation shown above occurs in Earth's atmosphere. In an experiment, [HO2][HO2] was monitored over time and the data plotted as shown in the following graph. Based on the information, which of the following is the rate law expression for the reaction?

Rate=k[HO2]2

The initial rates of the reaction represented by the equation shown above were measured for different initial concentrations of NO(g)NO(g) and Cl2(g)Cl2(g). Based on the data given in the table above, which of the following is the rate law expression for the reaction, and why?

Rate=k[NO]2[Cl2]Rate=k[NO]2[Cl2], because the initial rate quadrupled when [NO][NO] was doubled and doubled when [Cl2][Cl2] was doubled.

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the proposed mechanism, which of the following is the rate-law expression for the destruction of O3O3 ?

Rate=k[O3][Cl]

An experiment was conducted to determine the rate law for the reaction A2(g)+B(g)→A2B(g)A2(g)+B(g)→A2B(g). The table above shows the data collected. Based on the data in the table, which statement is correct?

Since the rate law can be expressed as rate=k[A2][B]rate=k[A2][B], doubling the concentrations of A2A2 and BB will quadruple the rate of the reaction.

The reaction between aqueous strontium chloride (SrCl2)(SrCl2) and aqueous potassium sulfate (K2SO4)(K2SO4) forms a precipitate of strontium sulfate (SrSO4)(SrSO4). Which of the following represents the net ionic equation for the reaction?

Sr2+(aq)+SO42−(aq)→SrSO4(s)

Which of the following statements, if true, would support the claim that the NO3−NO3− ion, represented above, has three resonance structures?

The NO3−NO3− ion is not a polar species.

2F2(g)+2NaOH(aq)→OF2(g)+2NaF(aq)+H2O(l)2F2(g)+2NaOH(aq)→OF2(g)+2NaF(aq)+H2O(l) A 2mol2mol sample of F2(g)F2(g) reacts with excess NaOH(aq)NaOH(aq) according to the equation above. If the reaction is repeated with excess NaOH(aq)NaOH(aq) but with 1 mol1 mol of F2(g)F2(g), which of the following is correct?

The amount of OF2(g)OF2(g) produced is halved.

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)H2(g)⁢+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)HI(g)⁢+ICl(g)→HCl(g)+I2(g)(fast) Question The reaction is carried out at constant temperature inside a rigid container. Based on this mechanism, which of the following is the most likely reason for the different rates of step 1 and step 2 ?

The amount of energy required for a successful collision between H2H2 and IClICl is greater than the amount of energy required for a successful collision between HIHI and IClICl.

A 1L1L sample of helium gas at 25°C25°C and 1atm1atm is combined with a 1L1L sample of neon gas at 25°C25°C and 1atm1atm. The temperature is kept constant. Which of the following statements about combining the gases is correct?

The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.

Which of the following scientific claims about the bond in the molecular compound HFHF is most likely to be true?

The bond is highly polar.

The elements CC and SeSe have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from CC and SeSe is most likely to be true?

The carbon-to-selenium bond is nonpolar covalent.

The diagrams above represent two samples of XeXe gas in containers of equal volume at 280K280K. Which of the following correctly compares the two samples in terms of their deviation from ideal gas behavior and explains why?

The gas in sample 2 would deviate more from ideal behavior because the average speed of the XeXe atoms is less, leading to an increase in intermolecular attractions.

C6H12O6+6O2→6CO2+6H2OC6H12O6+6O2→6CO2+6H2O The reaction between C6H12O6C6H12O6 and O2O2 is represented by the balanced equation above. In an experiment, 0.30mol0.30mol of CO2CO2 was produced from the reaction of 0.05mol0.05mol of C6H12O6C6H12O6 with excess O2O2. The reaction was repeated at the same temperature and in the same container, but this time 0.60mol0.60mol of CO2CO2 was produced. Which of the following must be true?

The initial amount of C6H12O6C6H12O6 in the container must have been 0.10mol0.10mol.

The gas-phase reaction A2(g)+B2(g)→2 AB(g) is assumed to occur in a single step. Two experiments were done at the same temperature inside rigid containers. The initial partial pressures of A2 and B2 used in experiment 1 were twice the initial pressures used in experiment 2. Which statement provides the best comparison of the initial rate of formation of AB in experiments 1 and 2 ?

The initial rate of formation of AB is faster in experiment 1 than in experiment 2 because at a higher pressure the collisions between A2 and B2 molecules would have been more frequent, increasing the probability of a successful collision.

A student is given two 10g10g samples, each a mixture of only NaCl(s)NaCl(s) and KCl(s)KCl(s) but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of KCl(s)KCl(s) ?

The mass of ClCl in each mixture

A 5.0g5.0g sample of MgCl2MgCl2 may contain measurable amounts of other compounds as impurities. Which of the following quantities is (are) needed to determine that the sample is pure MgCl2MgCl2 ?

The mass of MgMg and the mass of ClCl in the sample

Diagram 1 above shows equimolar samples of two gases inside a container fitted with a removable barrier placed so that each gas occupies the same volume. The barrier is carefully removed as the temperature is held constant. Diagram 2 above shows the gases soon after the barrier is removed. Which statement describes the changes to the initial pressure of each gas and the final partial pressure of each gas in the mixture and also indicates the final total pressure?

The partial pressure of each gas in the mixture is half its initial pressure; the final total pressure is half the sum of the initial pressures of the two gases.

Ar(g)Ar(g) deviates more from ideal behavior at extremely high pressures than Ne(g)Ne(g) does. Which of the following is one reason for this difference?

The particle volume of ArAr is greater than that of NeNe.

S2O82−(aq)+3I−(aq)→2SO42−(aq)+I3−(aq)S2O82−(aq)+3I−(aq)→2SO42−(aq)+I3−(aq) In aqueous solution, the reaction represented by the balanced equation shown above has the experimentally determined rate law: rate=k[S2O82−][I−]rate=k[S2O82−][I−]. If the concentration of [S2O82−][S2O82−] is doubled while keeping [I−][I−] constant, which of the following experimental results is predicted based on the rate law, and why? Responses

The rate of reaction will double, because the rate is directly proportional to [S2O82−][S2O82−].

A student was asked to formulate a hypothesis about what would happen if 100.mL100.mL of 0.1MNaOH(aq)0.1MNaOH(aq) at 25°C25°C was combined with 100.mL100.mL of 0.1MMgCl2(aq)0.1MMgCl2(aq) at 25°C25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?

The resulting solution would contain a precipitate.

Lewis diagrams of molecules of three different hydrocarbons are shown above. Which of the following claims about the molecules is best supported by the diagrams?

The strongest carbon-to-carbon bond occurs in molecule 3.

The diagrams above show the ultraviolet absorption spectra for two compounds. Diagram 1 is the absorption spectrum of pure acetone, a solvent used when preparing solutions for an experiment. Diagram 2 is the absorption spectrum of the solute for which the absorbance needs to be measured to determine its concentration. When the student reads the absorbance of the solution at 280nm280nm, the result is too high. Which of the following is most likely responsible for the error in the measured absorbance?

The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone.

HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l) A student had two dilute, colorless solutions, HCl(aq)HCl(aq) and NaOH(aq)NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?

The temperature of the reaction mixture increases.

Beta-carotene is an organic compound with an orange color. The diagram above shows the ultraviolet spectrum of beta-carotene. Which of the following statements is true about the absorption bands in the spectrum?

The two main absorption bands are associated with transitions in electronic energy levels. The band in the region corresponding to shorter wavelengths shows a lower absorbance than the band in the region corresponding to longer wavelengths.

MgCl2(aq)+2NaOH(aq)→2NaCl(aq)+Mg(OH)2(s)MgCl2(aq)+2NaOH(aq)→2NaCl(aq)+Mg(OH)2(s) A 100mL100mL sample of 0.1MMgCl2(aq)0.1MMgCl2(aq) and a 100mL100mL sample of 0.2MNaOH(aq)0.2MNaOH(aq) were combined, and Mg(OH)2(s)Mg(OH)2(s) precipitated, as shown by the equation above. If the experiment is repeated using solutions of the same molarity, which of the following changes in volume will double the amount of Mg(OH)2(s)Mg(OH)2(s) produced?

Using twice the volume of MgCl2(aq)MgCl2(aq) and twice the volume of NaOH(aq)NaOH(aq)

Two different ionic compounds each contain only copper and chlorine. Both compounds are powders, one white and one brown. An elemental analysis is performed on each powder. Which of the following questions about the compounds is most likely to be answered by the results of the analysis?

What is the formula unit of each compound?

Which of the following best helps explain why the electronegativity of ClCl is less than that of FF?

When ClCl and FF form bonds with other atoms, the ClCl bonding electrons are more shielded from the positive ClCl nucleus than the FF bonding electrons are shielded from the positive FF nucleus.

A student has samples of two pure compounds, XClO3XClO3 and ZClO3ZClO3, which contain unknown alkali metals XX and ZZ. The student measures the mass of each sample and then strongly heats the samples to drive off all the oxygen, leaving solid residues of XClXCl and ZClZCl. The student measures the mass of the solid residue from each sample. Which of the following questions can be answered from the results of the experiment?

Which has the greater molar mass, X or Z?

A student has two samples of NaClNaCl, each one from a different source. Assume that the only potential contaminant in each sample is KClKCl. The student runs an experiment to determine the percent by mass of chlorine in each sample. From the results of this experiment alone, which of the following questions is most likely to be answered?

Which sample has the higher purity?

A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are

equally shared and form nondirectional bonds

H2O2→H2O+12O2H2O2→H2O+12O2 Hydrogen peroxide decomposes to produce water and oxygen according to the equation above. An experimentally determined graph for the first-order decomposition of hydrogen peroxide is provided below. Which of the following best identifies the rate constant kk for the reaction based on the information in the plot of ln[H2O2]ln[H2O2] versus time (tt) ?

k=−(slope of plot)

The diagram above represents the photoelectric effect for a metal. Using the wavelength information provided above, what is the color of the light?

orange

Two pure elements react to form a compound. One element is an alkali metal, XX, and the other element is a halogen, ZZ. Which of the following is the most valid scientific claim that can be made about the compound?

It contains ionic bonds.

Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not?

It does not conduct electricity because its ions cannot move freely within the solid.

The diagram above is a molecular model of a gaseous diatomic element that is just above its boiling point. Intermolecular forces between the gas molecules will cause them to condense into the liquid phase if the temperature is lowered. Which of the following best describes how the model is limited in its depiction of the phenomenon?

It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

Molar mass of the compound, mass of the sample

Which statement best helps to explain the observation that NH3(l)NH3(l) boils at −28°C−28°C, whereas PH3(l)PH3(l) boils at −126°C−126°C?

NH3NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3PH3.

Which of the following best helps explain why the pressure of a sample of CH4(g)CH4(g) (molar mass 16g/mol16g/mol) is closer to the pressure predicted by the ideal gas law than a sample of NH3(g)NH3(g) (molar mass 17g/mol17g/mol) ?

NH3NH3 molecules are polar while CH4CH4 molecules are not, and the greater attractions between NH3NH3 molecules cause the molecules to collide with the walls of the container with less force.

The proposed rate-determining step for a reaction is 2 NO2(g)→NO3(g)+NO(g). The graph above shows the distribution of energies for NO2(g) molecules at two temperatures. Based on the graph, which of the following statements best explains why the rates of disappearance of NO2(g) are different at temperature 2 and temperature 1 ?

NO2(g) is consumed at a faster rate at temperature 2 because more molecules possess energies at or above the minimum energy required for a collision to lead to a reaction compared to temperature 1.

The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaFNaF and MgF2MgF2 is shown in the table above. On the basis of Coulomb's law, which of the following best helps to explain the large difference between the lattice energies of NaFNaF and MgF2MgF2 ?

The charge of the MgMg cation is larger than that of the NaNa cation.

Step 1:??(slow)Step 2:NO3(g)+CO(g)→NO2(g)+CO2(g)NO3(g)+CO(g)→NO2(g)+CO2(g)(fast)Overall:NO2(g)+CO(g)→NO(g)+CO2(g)NO2(g)+CO(g)→NO(g)+CO2(g) A two-step reaction mechanism is proposed for a gas-phase reaction, as represented above. Which of the following correctly identifies both the chemical equation for step 1 and the rate law for the overall reaction?

The chemical equation for step 1 is 2NO2(g)→NO(g)+NO3(g)2NO2(g)→NO(g)+NO3(g), and the rate law is rate=[NO2]2rate=[NO2]2.

Based on the proposed mechanism, which of the following best describes the concentration of the species represented above as the reaction occurs?

The concentration is very low for the duration of the reaction.

The photoelectron spectrum for the element nitrogen is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom?

The electrons in the 2p2p sublevel have the smallest binding energy.

Infrared spectroscopy is a useful tool for scientists who want to investigate the structure of certain molecules. Which of the following best explains what can occur as the result of a molecule absorbing a photon of infrared radiation?

The energies of infrared photons are in the same range as the energies associated with different vibrational states of chemical bonds. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the types and strengths of different bonds in the molecules.

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?

The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.

The graph above shows the distribution of molecular speeds for four different gases at the same temperature. What property of the different gases can be correctly ranked using information from the graph, and why?

The molecular masses of the gases, because the gas molecules have the same average kinetic energy and mass can be calculated using the equation KEavg=12mv2KEavg=12mv2.

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)H2(g)⁢+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)HI(g)⁢+ICl(g)→HCl(g)+I2(g)(fast) Which of the following represents the overall chemical equation for the reaction and the rate law for elementary step 2 ?

The overall reaction is H2(g)+2ICl(g)→2HCl(g)+I2(g)H2(g)+2ICl(g)→2HCl(g)+I2(g); the rate law for step 2 is rate=k[HI][ICl]rate=k[HI][ICl].

Using a spectrophotometer, a student measures the absorbance of four solutions of CuSO4CuSO4 at a given wavelength. The collected data is given in the table above. Which of the following is the most likely explanation for the discrepant data in trial 4 ?

The solution was saturated and the flow of light through the solution was restricted.

Four different liquid compounds in flasks at 20°C20°C are represented above. The table below identifies the compounds. Flask C shows the most particles in the vapor phase. Which of the following is not shown in the model but best helps to explain why flask C must contain pentane?

The strength of the intermolecular forces between the particles in the liquids

All the chlorides of the alkaline earth metals have similar empirical formulas, as shown in the table above. Which of the following best helps to explain this observation?

The two valence electrons of alkaline earth metal atoms are relatively easy to remove.

Which of the following best helps to explain why the electron affinity of BrBr has a greater magnitude than that of II?

There is a greater attraction between an added electron and the nucleus in BrBr than in II.

A student uses visible spectrophotometry to determine the concentration of CoCl2(aq)CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq)CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. The student made the standard curve above. Which of the following most likely caused the error in the point the student plotted at 0.050MCo2+(aq)0.050MCo2+(aq) ?

There was distilled water in the cuvette when the student put the standard solution in it.

Which of the following represents an electron configuration that corresponds to the valence electrons of an element for which there is an especially large jump between the second and third ionization energies? (Note: nn represents a principal quantum number equal to or greater than 2.)

ns2