AP Chem Midterm Questions
Which of the following Lewis diagrams best represents the bonding in the N2ON2O molecule, considering formal charges?
** N(triple bond)N-O******
C(s)+H2O(g)→CO(g)+H2(g)ΔH°=+131kJ/molrxnC(s)+H2O(g)→CO(g)+H2(g)ΔH°=+131kJ/molrxn The reaction between C(s)C(s) and H2O(g)H2O(g) is represented by the balanced chemical equation above. Based on the enthalpy change of the reaction (ΔH°ΔH°) and the standard heats of formation (ΔH°fΔHf°) given in the table below, what is the approximate ΔH°fΔHf° for CO(g)CO(g) ?
-111 kJ/mol
Shown above are the equation representing the decomposition of H2O2(l) and a table of bond enthalpies. On the basis of the information, which of the following is the enthalpy of decomposition of 2 mol of H2O2(l) ?
-203 k/J
The mass spectrum of the element Sb is most likely represented by which of the following?
121 and 123 amu
In an experiment to determine the specific heat of a metal, a student transferred a sample of the metal that was heated in boiling water into room-temperature water in an insulated cup. The student recorded the temperature of the water after thermal equilibrium was reached. The data are shown in the table above. Based on the data, what is the calculated heat qq absorbed by the water reported with the appropriate number of significant figures?
1640J
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 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?
2.25atm, because doubling the number of moles of ArAr doubles its partial pressure.
For an experiment, 50.0g50.0g of H2OH2O was added to a coffee-cup calorimeter, as shown in the diagram above. The initial temperature of the H2OH2O was 22.0°C22.0°C, and it absorbed 300.J300.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 H2OH2O after thermal equilibrium was reached? Assume that the specific heat capacity of H2OH2O is 4.2J/(g⋅K)4.2J/(g⋅K).
23.4°C
In the following diagrams, elements are represented by XX and ZZ, which form molecular compounds with one another. Which diagram represents a molecule that has a bent molecular geometry?
4 electron pairs around X - Z
An equation representing the dissociation of O2(g)O2(g) and a table of bond enthalpies are shown above. Based on the information, which of the following is the enthalpy of dissociation for O2(g)O2(g) ?
495kJ/mol
A student mixes 50mL50mL of 1.0MHCl1.0MHCl and 50mL50mL of 1.0MNaOH1.0MNaOH in a coffee-cup calorimeter and observes the change in temperature until the mixture reaches thermal equilibrium. The initial and final temperatures (°C)(°C) of the mixture are shown in the diagram above of the laboratory setup. Based on the results, what is the change in temperature reported with the correct number of significant figures?
5.5°C
The particle-level diagram above represents the structure of solid KF. Although the molar mass of KCl is greater than that of KF, the density of KCl is actually less than that of KF. Which of the following representations of the structure of KCl best helps to explain this phenomenon?
A - (left to right) + - + - + - + - +
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.
The elements C and Se have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from C and Se is most likely to be true?
A molecule of the compound will have a partial negative charge on the carbon atom.
A gas mixture at 0°C and 1.0atm contains 0.010mol of H2, 0.015mol of O2, and 0.025mol of N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture?
About 0.20atm, because H2 comprises 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 20.0g
If Na reacts with chlorine to form NaCl, which of the following elements reacts with Na to form an ionic compound in a one-to-one ratio, and why?
Br, because it has the same number of valence electrons as Cl
Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°?
C2H4O2 (as a picture)
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?
Cl2(g) reacts with metal atoms to form strong, covalent double bonds.
RbCl has a high boiling point. Which of the following compounds is also likely to have a high boiling point, and why?
CsCl, because its elements have very different electronegativities and it is an ionic compound.
The diagrams above represent solutes present in two different dilute aqueous solutions before they were mixed. Water molecules are not shown. When the solutions were combined, a precipitation reaction took place. Which of the diagrams below is the best particle representation of the mixture after the precipitation reaction occurred?
D; free- floating Na+ and NO3- ions, clumped Ag+ and Cl- ions
Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?
F−(aq)+H+(aq)→HF(aq)
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
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 C6H6 molecule, all the bonds between the carbon atoms have the same length.
Two pure elements react to form a compound. One element is an alkali metal, X, and the other element is a halogen, Z. 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.
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 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?
Mg with 14 neutrons
Which of the following elements has the mass spectrum represented above?
Mo
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
When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. The reaction is correctly classified as which of the following types?
Oxidation-reduction, because H2(g) is oxidized
I2(aq)+C6H8O6(aq)→C6H6O6(aq)+2I−(aq)+2H+(aq)I2(aq)+C6H8O6(aq)→C6H6O6(aq)+2I−(aq)+2H+(aq) The compound C6H8O6C6H8O6 reacts with I2I2 according to the reaction represented by the equation above. The reaction is correctly classified as which of the following types?
Oxidation-reduction, because I2I2 is reduced.
Equal volumes of 0.2M solutions of lead(II) nitrate and potassium bromide are combined to form lead(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)
Equal volumes of 0.2M0.2M 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)
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)
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) produced is halved.
A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. 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 HF is most likely to be true?
The bond is highly polar
The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaF and MgF2 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 NaF and MgF2 ? Responses
The charge of the Mg cation is larger than that of the Na cation
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 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 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 2p sublevel have the smallest binding energy
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 C6H12O6 in the container must have been 0.10mol.
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=1/2 mv2.
Which of the following statements, if true, would support the claim that the NO3− ion, represented above, has three resonance structures?
The oxygen-to-nitrogen-to-oxygen bond angles are 90°.
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.
A student was asked to formulate a hypothesis about what would happen if 100.mL of 0.1MNaOH(aq) at 25°C was combined with 100.mL of 0.1MMgCl2(aq) at 25°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.
HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l) A student had two dilute, colorless solutions, HCl(aq) and 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.
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) and twice the volume of NaOH(aq)
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) ?
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) ?
Steel is an alloy containing FeFe atoms and CC atoms. Which of the following diagrams best represents the particle-level structure of steel? Responses
diagram showing large white circles for FE and small grey circles for C in the gaps of the white circles
Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms?
diagram with many white circles and a few grey circles - all the same size circles
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
The oxidation of carbon monoxide can be represented by the chemical equation 2 CO(g)+O2(g)→2 CO2(g). The table above provides the average bond enthalpies for different bond types. Based on the information in the table, which of the following mathematical expressions is correct for the estimated enthalpy change for the reaction?
ΔHrxn=[2(1072kJmol)+(498kJmol)]−4(799kJmol).
Based on the information in the table above, which of the following expressions gives the approximate ΔH°ΔH° for the reaction represented by the following balanced chemical equation? Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g)
ΔH°rxn=[2(0kJ/mol)+3(−394kJ/mol)]−[(−826kJ/mol)+3(−111kJ/mol)]
The enthalpy change for the reaction 2Al(s)+Fe2O3(s)→2Fe(s)+Al2O3(s)2Al(s)+Fe2O3(s)→2Fe(s)+Al2O3(s) is −860kJ/mol−860kJ/mol. Based on the standard enthalpies of formation ΔH∘fΔHf° provided in the table, what is the approximate ΔH∘fΔHf° for Fe2O3(s)Fe2O3(s) ?
−820kJ/mol