AP CHEM WOOOOO (MCQ)
UNIT 5
UNIT 5
UNIT 6
UNIT 6
UNIT 7
UNIT 7
UNIT 8
UNIT 8
What is the standard enthalpy change for the reaction represented below? 3 C2H2 (g) --> C6H6 (g) deltaHC2H2 = 230 kJ mol-1 deltaHC6H6 = 83 kJ mol-1 a) -607 kJ b) -147 kJ c) -19 kJ d) +19 kJ
a) -607 kJ
A reaction was observed for 20 days and the percentage of the reactant remaining after each day was recorded in the table above. Which of the following best describes the order and the half-life of the reaction? a) 1st - 3 days b) 1st - 10 days c) 2nd - 3 days d) 2nd - 10 days
a) 1st - 3 days
In a saturated solution of Zn(OH)2 at 25°C, the value of [OH-] is 2.0 x 10-6 M. What is the value of the solubility-product constant, Ksp, for Zn(OH)2 at 25°C ? a) 4.0 x 10⁻¹⁸ b) 8.0 x 10⁻¹⁸ c) 1.6 x 10⁻¹⁷ d) 4.0 x 10⁻¹²
a) 4.0 x 10⁻¹⁸
A student mixes 50mL of 1.0MHCl and 50mL of 1.0MNaOH in a coffee-cup calorimeter and observes the change in temperature until the mixture reaches thermal equilibrium. The initial and final temperatures (°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? a) 5.5°C b) 5.50°C c) 5.800°C d) 6°C
a) 5.5°C
When the chemical reaction 2 NO (g) + O2 (g) --> 2 NO2 (g) is carried out under ceratin conditions, the rate of disappearance of NO (g) is 5.0 x 10⁻⁵ Ms⁻¹. What is the rate of disappearance of O2 (g) under the same conditions? a) Because two molecules of NO are consumed per molecule of O2, the rate of disappearance of O2 is 2.5 x 10⁻⁵ Ms⁻¹. b) Because two molecules of NO are consumed per molecule of O2, the rate of disapperance of O2 (g) is 1.0 x 10⁻⁴ Ms⁻¹. c) Because the rate depends on [NO]² and [O2], the rate of disappearance of O2 (g) is 2.5 x 10⁻⁹ Ms⁻¹. d) Because the O2 (g) is under the same experimental conditions as NO, it is consumed at the same rate of 5.0 x 10⁻⁵ Ms⁻¹.
a) Because two molecules of NO are consumed per molecule of O2, the rate of disappearance of O2 is 2.5 x 10⁻⁵ Ms⁻¹.
The oxidation of NO (g) is represented by the chemical equation below. 2 NO (g) + O2 (g) --> 2 NO2 (g) The initial concentrations of NO and O2 are given in the table below. The changes in concentration of NO (g) as a function of time are shown in the following graph. **negative exponential graph, time vs [NO]** Initial Concentration of NO = 0.0028 M Initial Concentration of O2 = 0.0014 M Under the same conditions, one of the following graphs represents the changes in concentration of O2 (g) over the same time interval. Which graph best represents the changes in [O2] and why? Graph 1 = **negative exponential graph, time vs [O2]** Graph 2 = **horizontal graph, time vs [O2]** a) Graph 1, because the rate of O2 consumption is half the rate at which NO is consumed; two molecules of NO react for each molecule of O2 that reacts. b) Graph 1, because O2 molecules are consumed at a slower rate at the beginning of the reaction when there are not as many molecules of NO2 produced. c) Graph 2, because there is a large excess of O2 molecules and its concentration will not change drastically over time. d) Graph 2, because a collision between three molecules to form a product has a low probability and the concentration of O2 will remain relatively small.
a) Graph 1, because the rate of O2 consumption is half the rate at which NO is consumed; two molecules of NO react for each molecule of O2 that reacts.
The table below lists some equilibrium systems and their equilibrium constants. Which of the following identifies the correct mathematical relationship that uses the information to calculate K5? **sorry not showing every option :(**
a) K5 = (K1)(K2)/K4
2NO(g) + O2(g)→N2O2(g) A possible mechanism for the overall reaction represented above is the following. NO(g) + NO(g) → N2O2(g) slow step N2O2(g) + O2(g) → 2NO2(g) fast step Which of the following rate expressions agrees best with this possible mechanism? a) Rate = k[NO]² b) Rate = k[NO]/[O2] c) Rate = k[NO]²[O2] d) Rate = k[N2O2][O2]
a) Rate = k[NO]²
A student adds 50.0g of liquid water at 25.0°C to an insulated container fitted with a temperature probe. The student then adds 10.0g of ice at 0.0°C, closes the container, and measures the temperature at different intervals. Part of the data is shown in the graph above. The student predicts that the temperature will continue to decrease then level out to a constant temperature. Which of the following best explains why the student's prediction is correct? **too much to write :(**
a) The H2O molecules initially in the ice and the molecules initially in the liquid will have the same average kinetic energy.
Which of the following best describes what happens to the substance between t4 and t5? a) The molecules are leaving the liquid phase. b) The solid and liquid phases coexist in equilibrium. c) The vapor pressure of the substance is decreasing. d) The average intermolecular distance is decreasing.
a) The molecules are leaving the liquid phase.
The oxidation of iodide ions by arsenic acid in acidic aqueous solution occurs according to the stoichiometry shown below. H3AsO4 + 3 I⁻ + 2 H3O⁺ --> H3AsO3 + 3 I + H2O According to the rate law for the reaction, an increase in the concentration of hydronium ions (H3O⁺) has what effect on this reaction? a) The rate of the reaction increases. b) The rate of reaction decreases. c) The value of the equilibrium constant increases. d) Neither the rate nor the value of the equilibrium constant is changed.
a) The rate of the reaction increases.
A → X The enthalpy change for the reaction represented above is ΔHT . This reaction can be broken down into a series of steps as shown in the diagram. What relationship must exist among the various enthalpy changes? a) ΔHT - ΔH1 - ΔH2 - ΔH3 = 0 b) ΔHT + ΔH1 + ΔH2 + ΔH3 = 0 c) ΔH3 - (ΔH1 + ΔH2 ) = ΔHT d) ΔH2 - (ΔH3 + ΔH1 ) = ΔHT
a) ΔHT - ΔH1 - ΔH2 - ΔH3 = 0
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 q absorbed by the water reported with the appropriate number of significant figures? a) 1600J b) 1640J c) 1642J d) 1642.3J
b) 1640J
NO (g) and O2 (g) react to form NO2 (g). The rate law of the reaction is rate = k[NO]²[O2]. If the reaction occurs in a single elementary step, then which of the following is the equation for the elementary step? a) N + O + O --> NO2 b) 2 NO + O2 --> 2 NO2 c) N + O2 --> NO2 d) N2 + 2 O2 --> 2 NO2
b) 2 NO + O2 --> 2 NO2
At a certain temperature, the value of the equilibrium constant K, for the reaction represented below is 2.0 x 10. What is the value of K for the reverse reaction at the same temperature? H2 (g) + Br2 (g) ⇌ 2 HBr (g) a) -2.0 x 10⁻⁵ b) 5.0 x 10⁻⁶ c) 2.0 x 10⁻⁵ d) 5.0 x 10⁻⁴
b) 5.0 x 10⁻⁶
The isomerization of cyclopentane to propylene is a 1st-order process with a half-life of 19 minutes at 500 C. The time it takes for the partial pressure of cyclopentane to decrease from 1.0 atom to 0.125 atm at 500 C is closest to which of the following? a) 38 minutes b) 57 minutes c) 76 minutes d) 152 minutes
b) 57 minutes.
The half-life of ⁵⁵Cr is about 2.0 hours. The delivery of a sample of this isotope from the reactor to a certain laboratory requires 12 hours. About what mass of such material should be shipped in order that 1.0 mg of ⁵⁵Cr is delivered to the laboratory? a) 130 mg b) 64 mg c) 32 mg d) 11 mg
b) 64 mg
HgO(s) + 4 I− + H2O ⇄ HgI42− + 2 OH− Consider the equilibrium above. Which of the following changes will increase the concentration of HgI42−? a) Increasing the concentration of OH− b) Adding 6 M HNO3 c) Increasing the mass of HgO present d) Adding a catalyst
b) Adding 6 M HNO3
Addition Cl2(g) is injected into the system at equilibrium. Which of the following graphs best shows the rate of the reverse reaction as a function of time? **idk how to list the graphs so...**
b) Answer will be Option B (Graph B).
Step 1: Ce4+ + Mn2+ → Ce3+ + Mn3+ Step 2: Ce4+ + Mn3+ → Ce3+ + Mn4+ Step 3: Mn4+ + Tl+ → Tl3+ + Mn2+ The proposed steps for a catalyzed reaction between Ce4+ and Tl+ are represented above. The products of the overall catalyzed reaction are...? a) Ce⁴⁺ + Tl⁺ b) Ce³⁺ + Tl³⁺ c) Ce³⁺ + Mn³⁺ d) Ce³⁺ + Mn⁴⁺
b) Ce³⁺ + Tl³⁺
Which of the following changes alone would cause a decrease in the value of Keq for the reaction represented below? a) Decreasing the temperature b) Increasing the temperature c) Decreasing the volume of the reaction vessel d) Increasing the volume of the reaction vessel
b) Increasing the temperature
The graph below shows the results of a study of the reaction of X with a large excess of Y to yield Z. The concentrations of X and Y were measured over a period of time. According to the results, which of the following can be concluded about the rate law for the reaction under the conditions studied? a) It is zero-order in [X]. b) It is first-order in [X]. c) It is second-order in [X]. d) The overall reaction order is 2.
b) It is first-order in [X].
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? a) It is not possible to determine that the system has reached equilibrium by 300s because the stoichiometry of the reaction is not known. b) It is not possible to determine that the system has reached equilibrium by 300s because the amounts of X, Y, and XY have continued to change. c) The system has reached equilibrium by 300s because the rate of formation of XY is constant. d) The system has reached equilibrium by 300s because the rates of consumption of X and Y are equal.
b) It is not possible to determine that the system has reached equilibrium by 300s because the amounts of X, Y, and XY have continued to change.
Which of the following statements about Kp, the equilibrium constant for the reaction, is correct? a) Kp > 1 b) Kp < 1 c) Kp = 1 d) It cannot be determined without additional information.
b) Kp < 1
The initial-rate data in the table above were obtained for the reaction represented below. What is the experimental rate law for the reaction? 2 NO (g) + O2 (g) → NO2 (g) a) Rate = k[NO][O2] b) Rate = k[NO][O2]² c) Rate = k[NO]²[O2] d) Rate = k[NO]²[O2]²
b) Rate = k[NO][O2]²
An experiment was conducted to determine the rate law for the reaction below. A2 (g) + B (g) --> A2B(g) The table shows the data collected. Based on the data in the table, which statement is correct? a) Since the rate law can be expressed as rate = k[A2]², tripling the concentration of A2 will cause a 9-fld increase in the rate of reaction. b) Since the rate law can be expressed as rate = k[A2][B], doubling the concentrations of A2 and B will quadruple the rate of reaction. c) Since the rate law can be expressed as rate = k[A2]²[B], tripling the concentration of A2 while keeping the concentration of B constant will triple the rate of reaction. d) Since the rate law can be expressed as rate = k[A2][B]². doubling the concentration of B while keeping the concentration of A2 constant will double the rate of reaction.
b) Since the rate law can be expressed as rate = k[A2][B], doubling the concentrations of A2 and B will quadruple the rate of reaction.
2 N2O5 (g) → 4 NO2 (g) + O2 (g) A sample of N2O5 was placed in an evacuated container, and the reaction represented above occurred. The value of PN2O5, the partial pressure of N2O5(g), was measured during the reaction and recorded in the table below. Which of the following correctly describes the reaction? a) The decomposition of N2O5 is a zero-order reaction. b) The decomposition of N2O5 is a first-order reaction. c) The decomposition of N2O5 is a second-order reaction. d) The overall reaction is 3.
b) The decomposition of N2O5 is a first-order reaction.
A 100 g sample of a metal was heated to 100C° and then quickly transferred to an insulated container holding 100 g of water at 22C°. The temperature of the water rose to reach a final temperature of 35C°. Which of the following can be concluded? a) The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained. b) The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained. c) The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water. d) The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.
b) The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.
X(g)+Y(g)⇄XY(g) In an experiment, X(g) and Y(g) were combined in a rigid container at constant temperature and allowed to react as shown in the equation above. The table provides the data collected during the experiment. Based on the data, which of the following claims is most likely correct? a) The reaction was about to reach equilibrium 15 minutes after the reactants were combined because the concentrations of X and XY were almost the same. b) The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations of X and Y remained constant. c) The reaction did not reach equilibrium because only 86% of the initial concentration of X was consumed. d) The reaction did not reach equilibrium because initially there was no XY inside the container.
b) The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations of X and Y remained constant.
The diagram above represents the equilibrium between the two isomers of C2H2Cl2, and the table provides the data collected in an experiment to determine its equilibrium constant, Kc, at 490K. In a second experiment done at the same temperature, [Z]eq≈1.0 M. Which of the following is the approximate equilibrium concentration of Y in the second experiment, and why? a) [Y]eq≈1.4 M because [Y]eq−[Z]eq should be the same for the same reaction. b) [Y]eq≈1.5 M because the ratio [Z]eq[Y]eq should remain constant when the reaction is done at the same temperature. c) [Y]eq≈1.6 M because the ratio [Y]initial[Y]eq should remain constant when the reaction is done at the same temperature. d) [Y]eq≈2.0 M because ([Y]initial−[Y]eq)=([Z]initial−[Z]eq) should be the same for the same reaction.
b) [Y]eq≈1.5 M because the ratio [Z]eq/[Y]eq should remain constant when the reaction is done at the same temperature.
The substance is at its normal freezing point at which time? a) t1 b) t2 c) t3 d) t4
b) t2
Which of the values of ∆H o for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)? a) z only b) y and z only c) x, y, and z only d) w, x, y, and z
b) y and z only
The rate constant (k) for the decay of the radioactive isotope I-131 is 3.6 x 10⁻³ hours⁻¹. The slope of which of the following graphs is correct for the decay and could be used to confirm the value of k? a) **positive linear graph, time vs 1/[1-131]** b) **negative linear graph, time vs 1/[I-131]²** c) **negative linear graph, time vs ln[I-131]** d) **negative linear graph, time vs [I-131]
c) **negative linear graph, time vs ln[I-131]**
How much heat is released or absorbed when 0.050 mol of Cl2 (g) is formed from KCl(s)? a) 87.4 kJ is released b) 43.7 kJ is released c) 43.7 kJ is absorbed d) 87.4 kJ is absorbed
c) 43.7 kJ is absorbed
The rate of a certain chemical reaction between substances M and N obeys the rate law above. The reaction is first studied with [M] and [N] each 1 x 10⁻³ molar. If a new experiment is conducted with [M] and [N] each 2 x 10⁻³ molar, the reaction rate will increase by a factor of...? Rate = k[M][N]² a) 2 b) 4 c) 8 d) 16
c) 8
Which of the following changes to the equilibrium system will increase the quantity of HI (g) in the equilibrium mixture? H2 (g) + I2 (g) ⇄ 2 HI (g) deltaH > 0 I. Adding H2(g) II. Increasing the temperature III. Decreasing the pressure a) I only b) III only c) I and II only d) I, II, and III
c) I and II only
How is the rate of the forward reaction affected as the reaction progresses toward equilibrium? a) It increases until it becomes the same as the reverse reaction rate at equilibrium b) It stays constant before and after equilibrium is reached c) It decreases to become a constant nonzero rate at equilibrium d) It decreases to become zero at equilibrium
c) It decreases to become a constant nonzero rate at equilibrium
2HI(g)⇄H2(g)+I2(g) Kp= (PH2)(PI2)/PHI)² =0.0016 The decomposition of HI(g) at 298K is represented by the equilibrium equation above. When 100.torr of HI(g) is added to a previously evacuated, rigid container and allowed to reach equilibrium, the partial pressure of I2(g) is approximately 3.7torr. If the initial pressure of HI(g) is increased to 200.torr and the process is repeated at the same temperature, which of the following correctly predicts the equilibrium partial pressure of I2(g), and why? a) PI2≈14 torr, because it is directly proportional to the square of the initial pressure of HI. b) PI2≈0.073 torr, because it is inversely proportional to the square of the initial pressure of HI. c) PI2≈7.4 torr, because it is directly proportional to the initial pressure of HI. d) PI2≈1.9 torr, because it is inversely proportional to the initial pressure of HI.
c) PI2≈7.4 torr, because it is directly proportional to the initial pressure of HI.
Step 1. N2H2O2 ⇄ N2HO2- + H+ (fast equilibrium) Step 2. N2HO2- → N2O + OH- (slow) Step 3. H+ + OH- → H2O (fast) Nitramide, N2H2O2, decomposes slowly in aqueous solution. This decomposition is believed to occur according to the reaction mechanism above. The rate law for the decomposition of nitramide that is consistent with this mechanism is given by which of the following? a) Rate = k[N2H2O2] b) Rate = k[N2H2O2][H+] c) Rate = k[N2H2O2]/[H+] d) Rate = k[N2H2O2]/[N2HO2]
c) Rate = k[N2H2O2]/[H+]
When the concentration of substance B in the reaction below is doubled, all other factors being held constnat, it is found that the rate of the reaction remains unchanged. What is the most probable explanation for this observation? 2 A (g) + B (g) --> 2 C (g) a) The order of the reaction with respect to substance B is 1. b) Substance B is not involved in any of the steps in the mechanism of the reaction. c) Substance B is not involved in the rate-determing step of the mechanism, but it is involved in subsequent steps. d) Substance B is probably a catalyst, and as such, its effect on the rate of the reaction does not depend on its concentration.
c) Substance B is not involved in the rate-determing step of the mechanism, but it is involved in subsequent steps.
HCl(aq)+H2O(l)⇄H3O+(aq)+Cl−(aq) In 1.0MHCl(aq), HCl is nearly 100 percent dissociated, as represented by the equation above. Which of the following best helps to explain why, in 0.01MHCN(aq), less than 1 percent of HCNis dissociated? a) The CN− ion is not very soluble in water, and a solid precipitate would form if more of the HCN dissociated. b) Compared to the HCl(aq) solution, the concentration of the HCN(aq) solution is much too dilute to achieve 100 percent dissociation. c) The equilibrium constant for the dissociation of HCN(aq) is much smaller than that for the dissociation of HCl(aq). d) HCN(aq) reacts with water to form a basic solution, and the high concentration of OH−(aq) interferes with the dissociation process.
c) The equilibrium constant for the dissociation of HCN(aq) is much smaller than that for the dissociation of HCl(aq).
The gas-phase reaction A2 (g) + B2 (g) --> 2 AB (g) is assumed to occur in a single step. Two experiments were performed 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? a) The initial rate of formation of AB is the same in both experiments because they were performed at the same temperature and the frequency and energy of the collisions between A2 and B2 would have been about the same. b) The initial rate of formation of AB is slower in Experiment 1 than in Experiment 2 because at the same temperature, a higher pressure would reduce the volume available for A2 and B2 molecules to achieve the proper orientation for a successful collision. c) The initial rate of formation of AB is faster in Experiment 1 than in Experiment 2 because at a higher pressure collisions between A2 and B2 molecules would have been more frequent, increasing the probability of a successful collision. d) The initial rate of formation of AB is faster in Experiment 1 than in Experiment 2 because at a higher pressure a larger fraction of A2 and B2 molecules would have the minimum energy required to overcome the activation energy barrier.
c) The initial rate of formation of AB is faster in Experiment 1 than in Experiment 2 because at a higher pressure collisions between A2 and B2 molecules would have been more frequent, increasing the probability of a successful collision.
The table above shows data for two reactions carried out in two separate evacuated 1.0-liter rigid containers at constant temperature of 298K. To each container 0.50mol of the appropriate reactants was added, and the reaction was allowed to reach equilibrium. Based on this information, which of the following correctly compares the relative concentrations of BrCl and NO present inside their respective containers at equilibrium? a) [BrCl]eq=[NO]eq because equimolecular mixtures of the reactants were allowed to reach equilibrium at the same constant temperature. b) [BrCl]eq>[NO]eq because Br2 and Cl2 are larger molecules that can collide more frequently to form products. c) [BrCl]eq>[NO]eq because the much larger Keq for reaction 1 means that a much higher concentration of products will be present at equilibrium for reaction 1 compared with reaction 2. d) [BrCl]eq<[NO]eq because the much larger Keq for reaction 1 means that hardly any products will be present at equilibrium compared with reaction 2.
c) [BrCl]eq>[NO]eq because the much larger Keq for reaction 1 means that a much higher concentration of products will be present at equilibrium for reaction 1 compared with reaction 2.
Hydrogen peroxide decomposes to produce water and oxygen according to the equation below. H2O2 --> H2O = O2 An experiementally determined graph for the 1st order decomposition of hydrogen peroxide is provided below. Which of the following best identifies the rate constant (k) for the reaction based on the information in the plot of ln[H2O2] versus time? **negative linear graph** a) k = ln[H2O2] at t = 0s b) k = ln[H2O2] at t = 500s c) k = -(slope of plot) d) k = -1/(slope of plot)
c) k = -(slope of plot)
The reaction represented by the chemical equation below occurs in the Earth's atmosphere. 2 HO2 (g) --> H2O2 (g) + O2 (g) In an experiment, [HO2] was monitored over time and the data plotted as shown in the graph below. **positive linear graph, time vs 1/[HO2]** Based on the information, which of the following is the rate law expression for the reaction? a) rate = k b) rate = k[HO2] c) rate = k[HO2]² d) rate = k[H2O2][O2]
c) rate = k[HO2]²
Which of the following expressions is equivalent to ΔH o for the reaction represented below? Cl2 (g) + 2e- → 2Cl- (g) a) x + y b) x - y c) x + 2y d) x/2 - y
c) x + 2y
A 2 mol sample of C2H5OH undergoes the phase transition illustrated in the diagram above. The molar enthalpy of vaporization, deltaHvap of C2H5OH is +38.6kj/mol. Which of the following best identifies the change in enthalpy in the phase transition shown in the diagram? a) +19.3 kJ b) +77.2 kJ c) -19.3 kJ d) -77.2 kJ
d) -77.2 kJ
The diagram above represents the melting of H2O(s). A 2.00mole sample of H2O(s) at 0°C melted, producing H2O(l) at 0°C. Based on the diagram, which of the following best describes the amount of heat required for this process and the changes that took place at the molecular level? a) 3.01kJ of heat was absorbed to decrease the average speed of the water molecules in the liquid, which decreases the distance between molecules. b) 6.02kJ of heat was absorbed to increase the number of hydrogen bonds between water molecules in the liquid compared to the solid. c) 12.0kJ of heat was absorbed to decrease the polarity of the water molecules, which increases the density of the liquid compared to the solid. d) 12.0kJ of heat was absorbed to overcome some of the hydrogen bonding forces holding the water molecules in fixed positions in the crystalline structure.
d) 12.0kJ of heat was absorbed to overcome some of the hydrogen bonding forces holding the water molecules in fixed positions in the crystalline structure.
For an experiment, 50.0g of H2O was added to a coffee-cup calorimeter, as shown in the diagram above. The initial temperature of the H2O was 22.0°C, and it absorbed 300.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 H2O after thermal equilibrium was reached? Assume that the specific heat capacity of H2O is 4.2J/(g⋅K). a) 21.3 C b) 22.0 C c) 22.7 C d) 23.4 C
d) 23.4 C
The reaction mixture represented below is at equilibrium at 298 K, and the molar concentrations are [X] = 2.0 M, [Y] = 0.5 M, and [Z] = 4.0 M. What is the value of the equilibrium constant for the reaction at 298 K? 2 X (g) + Y (g) ⇌ 3 Z (g) a) 2.0 b) 4.0 c) 16 d) 32
d) 32
Factors that affect the rate of a chemical reaction include which of the following? a) Frequency of collisions of reactant particles. b) Kinetic energy of collisions of reactant particles. c) Orientation of reactant particles during collisions. d) All three affect the rate of a chemical reaction.
d) All three affect the rate of a chemical reaction.
For a classroom demonstration, a chemistry teacher puts sample 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? a) An exothermic chemical change occurred because heat flowed from the contents of the beaker to the room. b) An exothermic physical change occurred because heat flowed from the contents of the beaker and the water on the board to the room. c) An endothermic physical change occurred because the freezing of the water is an endothermic process. d) An endothermic chemical change occurred because the temperature of the beaker an the water on the board decreased as heat was absorbed by the reaction.
d) An endothermic chemical change occurred because the temperature of the beaker an the water on the board decreased as heat was absorbed by the reaction.
A sample of N2O4(g) is placed into an evacuated container at 373K and allowed to undergo the reversible reaction N2O4(g)⇄2NO2(g). The concentration of each species is measured over time, and the data are used to make the graph shown above. Which of the following identifies when equilibrium is first reached and provides a correct explanation? a) At 14 seconds, because [N2O4] is twice [NO2], which implies that the forward and reverse reaction rates are equal. b) At 23 seconds, because [NO2] equals [N2O4], which shows that equal concentrations are present at equilibrium. c) At 40 seconds, because [NO2] is twice [N2O4], which matches the stoichiometry of the balanced chemical equation. d) At 60 seconds, because [NO2] and [N2O4] remain constant, indicating that the forward and reverse reaction rates are equal.
d) At 60 seconds, because [NO2] and [N2O4] remain constant, indicating that the forward and reverse reaction rates are equal.
A piece of Fe(s) at 25°C is placed into H2O(l) at 75°C in an insulated container. A student predicts that when thermal equilibrium is reached, the Fe atoms, being more massive than the H2O molecules, will have a higher average kinetic energy than the H2O molecules. Which of the following best explains why the student's prediction is incorrect? *too much to write :(**
d) At thermal equilibrium, the average kinetic energy of the Fe atoms cannot be greater than that of the H2O molecules; the average kinetic energies must be the same according to the definition of thermal equilibrium.
The energy diagram for the reaction X + Y --> Z is shown below. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences? a) I only b) II only c) III only d) I and II only
d) I and II only
Which of the following phase changes involves the transfer of heat from the surroundings to the system? **too much to write :(**
d) NH3(l)-- NH3(g), because NH3 molecules in the liquid phase must absorb energy in order to overcome their intermolecular attractions and become free gas molecules.
The initial rates of reaction represented by the equation below were measured for different initial concentrations of NO (g) and Cl2 (g). 2 NO(g) + Cl2 (g) --> 2 NOCl (g) Based on the data given in the table below, which of the following is the rate law expression for the reaction and why? a) Rate = k[NO]², because the intiial rate quadrupled when [NO] was doubled but remained constant when [Cl2] was doubled. b) Rate = k[NO][Cl2], because the initial rate doubled when either [NO] or [Cl2] was doubled. c) Rate = k[NO][Cl2]², because the initial rate doubled when [NO] was doubled and quadrupled when [Cl2] was doubled. d) Rate = k[NO]²[Cl2], because the initial rate quadrupled when [NO] was doubled and doubled when [Cl2] was doubled.
d) Rate = k[NO]²[Cl2], because the initial rate quadrupled when [NO] was doubled and doubled when [Cl2] was doubled.
2SO(g) <-> 2SO2(g) + O2(g) After the equilibrium represented above is established, some pure O2(g) is injected into the reaction vessel at a constant temperature. After equilibrium is reestablished, which of the following has a lower value compared to its value at the original equilibrium? a) Keq for the reaction b) The amount of SO3(g) in the reaction vessel c) The amount of O2(g) in the reaction vessel d) The amount of SO2(g) in the reaction vessel.
d) The amount of SO2(g) in the reaction vessel.
A sample of CHCI3 (s) was exposed to a constant source of heat for a period of time. The graph above shows the change in the temperature of the sample as heat is added. Which of the following best describes what occurs at the particle level that makes segment D longer than segment B? a) The specific heat capacity of the liquid is significantly higher than that of the solid, because the particles in the liquid state need to absorb more thermal energy to increase their average speed. b) The specific heat capacity of the solid is significantly higher than that of the gas, because the particles in the solid state need to absorb more thermal energy to increase their average speed. c) The enthalpy of fusion is greater than the enthalpy of vaporization, because separating molecules in their bound crystalline state requires more energy than separating molecules completely from the liquid state. d) The enthalpy of vaporization is greater than the enthalpy of fusion, because separating molecules completely from the liquid to form a gas requires more energy than separating molecules from their bound crystalline state to a liquid state.
d) The enthalpy of vaporization is greater than the enthalpy of fusion, because separating molecules completely from the liquid to form a gas requires more energy than separating molecules from their bound crystalline state to a liquid state.
In the spring, blossoms on cherry trees can be damaged when temperature fall below -2 degree. When the forecast calls for air temperatures to be below -5 degree for a few hours one night, a farmer sprays his blossoming cherry trees with water, claiming that the blossoms will be protected by the water as it freezes. Which of the following is a correct scientific justification for spraying water on the blossoms to protect them from temperatures below -2? a) Water on the blossoms will not freeze unless the air temperature falls significantly below -5 C. b) Water is a good thermal conductor that transfers heat from the cold air to the blossoms, keeping the blossoms from going below -2 C. c) The freezing of water is an endothermic process; thus, water that freezes on the blossoms absorbs heat from the atmosphere, which in turn keeps the blossoms above 0 C. d) The freezing of water is an exothermic process; thus, water that freezes on the blossoms releases heat to keep the blossoms at or above -2.
d) The freezing of water is an exothermic process; thus, water that freezes on the blossoms releases heat to keep the blossoms at or above -2.
Which of the following represents the overall chemical equation for the reaction and the rate law for elementary Step 2? Step 1: H2 (g) + ICl (g) --> HI (g) + HCl (g) Step 2: HI (g) + ICl (g) --> HCl (g) + I2 (g) a) The overall reaction is H2 (g) + 2 ICl (g) --> HCl (g) + I2 (g). The rate law for Step 2 is rate = k[H2][HI][ICl] b) The overall reaction is H2 (g) + 2 ICl (g) --> 2 HCl (g) + I2 (g). The rate law for Step 2 is rate = k[H2][ICl]² c) The overall reaction is H2 (g) + ICl (g) --> HCl (g) + I2 (g). The rate law for Step 2 is rate = k[H2][ICl] d) The overall reaction is H2 (g) + 2 ICl (g) --> 2 HCl (g) + I2 (g). The rate law for Step 2 is rate = k[HI][ICl]
d) The overall reaction is H2 (g) + 2 ICl (g) --> 2 HCl (g) + I2 (g). The rate law for Step 2 is rate = k[HI][ICl]
The graphs above show Maxwell-Boltzmann distributions for one-mole samples of Ar (g). Graph 1 shows the distribution of particle energies at 300K and graph 2 shows the distribution of particle energies at 600K. A student predicts that if the samples are combined in an insulated container and thermal equilibrium is attained, then the most probable particle energy will be between the most probable energy shown in graph 1 and the most probable energy shown in graph 2. Which of the following is the best justification for the student's claim? a) When the samples are combined, the gas particles will collide with one another, with the net effect being that the speed of the lowest energy particles decreases while the speed of the highest energy particles increases, leaving the average speed of the particles in the original samples unchanged. b) When the samples are combined, the gas particles from each sample will collide with the gas particles from the other sample until every particle in the mixture has the same speed, which is between the average speed of the particles in the hotter sample and the average speed of the particles in the cooler sample. c) When the samples are combined, the gas particles collide with one another until every particle in the mixture has the same kinetic energy, which is between the average kinetic energy of the particles in the hotter sample and the average kinetic energy of the particles in the cooler sample. d) When the samples are combined, the gas particles will collide with one another, with the net effect being that energy will be transferred from the more energetic particles to the less energetic particles until a new distribution of energies is achieved at a temperature between 300K and 600K.
d) When the samples are combined, the gas particles will collide with one another, with the net effect being that energy will be transferred from the more energetic particles to the less energetic particles until a new distribution of energies is achieved at a temperature between 300K and 600K.
What is the molar solubility in water of Ag2CrO4? (The Ksp for Ag2CrO4 is 8 X 10⁻¹².) a) 2 x 10⁻¹² M b) sqrt(4 x 10⁻¹²) M c) cbrt(4 x 10⁻¹²) M d) cbrt( 2 x 10⁻¹²) M
d) cbrt( 2 x 10⁻¹²) M
The cooling curve above shows how the temperature of a sample varies with time as the sample goes through phase changes. The sample starts as a gas, and heat is removed at a constant rate. At which time does the sample contain the most liquid? a) t1 b) t2 c) t3 d) t4
d) t4
