AP CHEM QUIZ 2

2H2O2(l) >> 2H2O (l) + O2 (g) bond ||| average bond enthalpy O-H ||| 463 O-O ||| 146 O=O ||| 495 shown above is the equation representing the decomposition of H2O2 (l) & a table of bond enthalpies. on the basis of the info, which is the enthalpy of decomposition of 2 mol of H2O2 (l)?

-203 kJ

Which ground state electron configuration represents the atom that has the lowest first-ionization energy?

1s^2 2s^2 2p^6 3s^1

Al(s) >> Al^3+ (aq) + 3e- Zn^2+ (aq) + 2e- >> Zn(s) The hald-rxns for the oxidation-reduction rxn between Al(s) & Zn^2+ (aq) are represented above. Based on the half-rxns, what is the coefficient for Al(s) if the equation for the oxidation-reduction rxn is balanced w/ the smallest whole # coefficients?

2

which numerical expression gives the # of particles in 2.0g of Ne?

2.0g/20.18 g/mol x (6.0x10^23) particles/mol)

Ni(s) >> Ni^2+ (aq) + 2e- Ag+ (aq) + e- >> Ag(s) Which of the following is the balanced net ionic equation for an oxidation-rxn between Ag+ (aq) & Ni (s) based on the half-rxns represented above?

2Ag+ (aq) + Ni (s) >> 2Ag(s) + Ni^2+ (aq)

O2(g) >> 2O(g) bond ||| average bond enthalpy O=O ||| 495 O-O ||| 146 an equation representing the dissociation of O2(g) & a table of bond enthalpies are shown above. based on the info, which is the enthalpy of dissociation for O2(g)?

495 kJ/mol

if Na reacts with Cl to form NaCl, which element reacts with Na to form an ionic compound in a 1:1 ratio, & why?

Br, b/c it has the same # of ve- as Cl.

RbCl has a high bp. Which compound is also likely to have a high bp, & why?

CsCl, b/c its elements have very different electronegativities & it is an ionic compound.

Which is the net ionic equation for the reaction between aqueous sodium fluoride & hydrochloric acid?

F- (aq) + H+ (aq) >> HF (aq)

which complete lewis diagrams represents a molecule containing a bond angle that is closes to 120*?

H O: H : C : C : O : H H

HCl(aq) + H2O(l) >> H3O+(aq) + Cl-(aq) for the dissolution of HCl in water represented above, which of the following pairs includes the Bronsted-Lowry bases?

H2O(l) & Cl-(aq)

graph in order: 100, 94, 97, 92, 95, 96, 98 which element has the mass spectrum represented above?

Mo

equal volumes of 0.2 M solutions of lead (II) nitrate & potassium bromide are combined to form lead (II) bromide as a yellow precipitate. which is the correct net ionic equation for the rxn?

Pb^2+ (aq) + 2Br- (aq) >> PbBr2(s)

the rxn between aqueous strontium chloride & aqueous potassium sulfate forms a precipitate of strontium sulfate. which represents the net ionic equation for the rxn?

Sr^2+ (aq) + SO4^2- (aq) >> SrSO4 (s)

2F2(g) + 2NaOH(aq) >> OF2(g) + 2NaF(aq) + H2O(l) A 2 mol sample of F2(g) reacts w/ excess NaOH(aq) according to the equation above. If the rxn is repeated w/ excess NaOH(aq) but w/ 1 mol of F2(g), which of the following is correct?

The amount of OF2(g) produced is halved.

The diagrams above represent solutes present in 2 different dilute aqueous solutions before they were mixed. Water molecules are not shown. When the solutions were combined, a precipitation rxn took place. Which of the diagrams below is the best particle representation of the mixture after the precipitation rxn occurred?

The box with all Ag- and Cl- at the bottom and most NO3- and Na+ at the top.

HCl(aq) + NaOH(aq) >> NaCl(aq) + H2O(l) a student has 2 dilute, colorless, solutions, HCl(aq) & NaOH(aq), which were at the same temp. the student combined the solutions, & the rxn represented above occurred. Which of the following results would be evidence that a chemical rxn took place?

The temp of the rxn mixture increases.

At night, an equilibrium reaction between two different nitrogen compounds generates N2O5 in the atmosphere, as represented below. Reaction 1: NO3(g)+NO2(g)⇄N2O5(g) K=2.6×10−11 during the day, solar radiation is absorbed by NO3(g), resulting in its decomposition. which best explains whether the equilibrium concentration of N2O5(g) in the atmosphere in the daytime is different from that in the nighttime, & why?

[N2O5] will be higher at night, b/c the decomposition of NO3(g) in the daytime will result in an increase in the rate of consumption of N2O5(g) to reform NO3(g).

A student mixes 20g of which KCl crystals w/ distilled water in a beaker. after the mixture was stirred, no crystals are visible & the solution is clear. after several days, all of the water evaporates & white crystals are found in the beaker. Which of the following pieces of experimental evidence would best help the student to confirm that a new compound hadn't been made& that only a physical change occurred?

after the water has evaporated, the white crystals in the beaker have a mass of 20.0g

For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation?

an endothermic chemical change occurred b/c the temp of the beaker & the water on the board decreases as heat was absorbed by the rxn.

a sample of N2O4(g) is placed into an evacuated container at 373K & allowed to undergo the reversible rxn N2O4 <> NO2. the concentration of each species is measured over time, & the data is used to make the graph shown above. which identifies when equilibrium is 1st reached & provides a correct explanation?

at 60 secs, b/c [NO2] & [N2O4] remain constant, indicating that the forward & reverse rxn rates are equal.

Bond type ||| average bond enthalpy C-C 360 C=O 799 C=-O 1072 O-O 142 O=O 498 the oxidation of carbon monoxide can be represented by the chemical equation 2CO(g) + O2(g) >> 2CO2(g). the table above provides the average bond enthalipies for different bond types. based on the info in the table, which mathematical expression is correct for the estimated enthalpy change for the rxn?

change in H rxn = [2(1072kj/mol) + (498kj/mol)] - 4(799kj/mol)

the mass spectrum of the element Sb is most likely represented by which of the following?

graph: high at 121 amu, little lower at 123 amu

An equimolar mixture of X(g) and Y(g) is placed inside a rigid container at constant temperature. The particle diagram above represents the changes that occur over time. Based on the particle diagram, which of the following best predicts whether or not the system has reached equilibrium by 300s?

it is not possible to determine that the system has reached equilibrium by 300s b/c the amounts of X,Y & XY have continued to change.

metal ||| Be ||| Mg ||| Ca ||| Sr ||| Ba ||| Ra formula ||| BeCl2 ||| MgCl2 ||| CaCl2 ||| SrCl2 ||| BaCl2 ||| RaCl2 of metal Cl all the Cl's of the alkaline earth metals have similar empirical formulas, as shown in the table above. Which best helps to explain this observation?

the 2 ve- of alkaline earth metal atoms are relatively easy to remove.

which scientific claim about the bond in the molecular compound HF is most likely to be true?

the bond is highly polar

A 5.0g sample of MgCl2 may contain measurable amounts of other compounds as impurities. Which of the following quantities is (are) needed to determine that the sample is pure MgCl2?

the mass of Mg & the mass of Cl in the sample.

mass of empty crucible - 12.0g mass of crucible & sample before heating - 14.4g mass of crucible & sample after heating - 16.0g a student places a sample of a pure metal in a crucible & 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 temp. Which statement is correct?

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

the particle diagram above illustrates the changes that take place when X(g) & Y(g) are placed inside a rigid container at constant temp. Which is a characteristic of a system at equilibrium this is best represented by the particle diagram?

the particle diagram shows that after 200s there are no observable changes in the amounts of reactants & products, which is a characteristic of a system at equilibrium.

a student was asked to formulate a hypothesis about what would happen if 100mL of 0.1 M NaOH(aq) at 25*C was combined w/ 100mL of 0.1 M MgCl2(aq) at 25*C. Which of the following hypothesis indicated that the student thought a chemical change would occur?

the resulting solution would contain a precipitate.

time ||| [X] ||| [XY] 0 ||| 5.0 x 10^-2 ||| 0.0 5 ||| 4.1 x 10^-2 ||| 9.0 x 10^-3 15 ||| 2.9 x 10^-2 ||| 2.1 x 10^-2 35 ||| 1.0 x 10^-2 ||| 4.0 x 10^-2 75 ||| 8.0 x 10^-3 ||| 4.2 x 10^-2 155 ||| 7.0 x x 10^-3 ||| 4.3 x 10^-2 375 ||| 7.0 x x 10^-3 ||| 4.3 x 10^-2 500 ||| 7.0 x x 10^-3 ||| 4.3 x 10^-2 in an experiment, X(g) & Y(g) were combined in a rigid container at constant temp & allowed to react as shown in the equation above. the table provides the data collected during the experiment. based on the data, which claim is most likely correct?

the rxn reached quilibrium between 75 mins & 155 mins after the reactant were combines b/c the concentrations of X & XY remained constant.