AP Chem Midterm

Consider the following processes: 2A → (1/2)B + C △H1 = 5 kJ/mol (3/2)B + 4C → 2A + C + 3D △H2 = -15 kJ/mol E + 4A →C △H3 = 10 kJ/mol Calculate △H for: C → E + 3D A) 0 kJ/mol B) 10 kJ/mol C) -10 kJ/mol D) -20 kJ/mol E) 20 kJ/mol

-10 kJ/mol

2NH3 (g) → 3H2 (g) + N2 (g) Consider the decomposition of NH3 gas in the equation above at constant room temperature and pressure. Compared to initial pressure, the final pressure exerted by the products will be A) 2 times greater B) 3 times greater C) the same as the initial pressure D) one-half the initial pressure

2 times greater

The figure above represents three sealed 1.0 L vessels, each containing a different inert gas at 298 K. The pressure of Ar in the first vessel is 2.0 atm. The ratio of the numbers of Ar, Ne, and He atoms in the vessels is 2:1:6, respectively. After all the gases are combined in a previously evacuated 2.0 L vessel, what is the total pressure of the gases at 298 K? A) 3.0 atm B) 4.5 atm C) 9.0 atm D) 19 atm

4.5 atm

The temperature of 36.0 mL of CH4 gas is raised from 27.0°C to 327°C at constant pressure. What is the final volume of the CH4 gas after heating? A) 18.0 mL B) 36.0 mL C) 72.0 mL D) 327 mL

72.0 mL

C2H6 (g) + 7/2 O2(g) → 2 CO2 (g) + 3H2O (g) If 6.00 g ethane, C2H6 (g) burn, what volume of CO2 (g) will be formed at STP? A) 0.200 L B) 2.20 L C) 9.00 L D) 22.4 L

9.00 L

2H2O2 (aq) --> 2H2O (l) + O2 (g) △H = -196 kJ/mol The decomposition of H2O2 (aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2 (aq) at a constant temperature of 300K and recorded the concentration of H2O2 as a function of time. The results are given in the table below Time(s) [H2O2] 0 2.7 200. 2.1 400. 1.7 600. 1.4 The O2 (g) produced from the decomposition of the 1.0 L sample of H2O2 (aq) is collected in a previously evacuated 10.0 L flask at 300 K. What is the approximate pressure in the flask after 400. s? A) 1.2 atm B) 2.4 atm C) 12 atm D) 24 atm

A) 1.2 atm

2H2S (g) + CH4 (g) ⇄ CS2 (g) + 4H2 (g) Kc = 3.4 x 10^-4 A 0.10 mol sample of each of the four species in the rxn represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest [ ] when the system reaches equilibrium? A) H2S (g) B) CH4 (g) C) CS2 (g) D) H2 (g)

A) H2S (g)

Cl (g) + O3 (g) ---> ClO (g) + O2 (g) slow step ClO (g) + O3 (g) ----> Cl (g) + 2 O2 (g) fast step 2 O3 (g) ---> 3 O2 (g) overall rxn which of the following rate laws for the overall rxn corresponds to the proposed mechanism? A) rate=k[O3]^2 B) rate=k[Cl][O3] C) rate=k[ClO][O3]^2 D)rate= k[O2]^3/[O3]^2

B) rate=k[Cl][O3]

N2O4 (g) <---> 2NO2 (g) Kp=2.0 at 70C colorless brown A mixutre of NO2 (g) and N2O4 (g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath? A) the forward rxn is exothermic B) the forward rxn is endothermic C) the ice bath lowered the activation energy D) the ice bath raised the activation energy

B) the forward rxn is endothermic

Cr2O7^2-(aq) + 3H2O(l)<--->2CrO4^2-(aq)+2H3O+(aq) orange yellow The equilibrium system represented by the equation above initially contains equal [ ]s of CrO7^2- (aq) and CrO4^2- (aq). Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH (aq) to the system and provides an explanation? A) The mixture will become more orange because OH-(aq) will oxidize the Cr in CrO4^2- (aq) B) The mixture will become more yellow because OH- (aq) will reduce the Cr in CrO7^2- (aq) C) The mixture will become more yellow because OH- (aq) will shift the equilibrium toward products D) The color of the mixture will not change because OH- (aq) does not appear in the equilibrium expression

C) The mixture will become more yellow because OH- (aq) will shift the equilibrium toward products

CO (g) + H2O(g) <--> CO2(g) +H2(g) Kc = 1.5 x 10^3 A 2.0 mol sample of CO(g) and a 2.0 mol sample of H2O(g) are introduced into a previously evacuated 100 L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium? A) [H20] > [CO] and [CO2] > [H2] B) [H20] > [H2] C) [CO2] > [CO] D) [CO] = [H2O] = [CO2] = [H2]

C) [CO2] > [CO]

X (g) + 2 Q (g) ⇄ R (g) + Z (g) Kc= 1.3 x 10^5 at 50C A 1.0 mol sample of X (g) and a 1.0 mol sample of Q (g) are introduced into an evacuated, rigid 10.0 L container and allowed to reach equilibrium at 50C according to the equation above. At equilibrium, which of the following is true about the concentrations of the gases? A) [R]= 1/2[Q] B) [Q] = 1/2 [X] C) [R]=[Z]>[Q] D)[X]=[Q]=[R]=[Z]

C) [R]=[Z]>[Q]

Cl-(aq) + ClO-(aq) + 2H+ ---> Cl2 (g) + H20 (l) what effect will increasing the [H+] at constant temp have on the rxn represented above? A) The activation energy of the rxn will increase B) the activation energy of the rxn will decrease C) the frequency of collisions btwn H+ (aq) ions and ClO- (aq) ions will increase D) the value of the rate constant will increase

C) the frequency of collisions btwn H+ (aq) ions and ClO- (aq) ions will increase

The sample below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4 On the basis of the data provided above, the gas in container 3 could be A) CH4 B) O2 C) Ar D) CO2

CH4

The sample below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4 Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is A) greatest in container 1 B) greatest in container 2 C) greatest in container 4 D) the same in containers 1, 2, and 4

Greatest in container 1

The ideal gas law best describes the properties of which of following gases at 0°C and 1 atm A) PH3 B) HBr C) SO2 D) N2

N2

When water is heated to boiling in an open soda can and the can is then inverted into a bucket containing cold water, A) the cab expands due to rapid expansion of the water vapor inside B) the can implodes due to the rapid change in room air pressure C) the can implodes due to rapid condensation of the inside water vapor D) the can implodes due to the rapid change in room air pressure and rapid condensation of the inside water vapor

the can implodes due to rapid condensation of the inside water vapor

Addition of 50 J to a 10.0 g sample of a metal will cause the temperature of the metal to rise from 25°C to 35°C. The specific heat c of the metal is closest to A) 5.0 x 10^-4 J/(g ℃) B) .50 J/(g ℃) C) 2.5 J/(g ℃) D) 4.2 J/(g ℃)

0.50 J/(g °C)

The standard enthalpy change of formation for nitrogen dioxide is the enthalpy change of the reaction A) 1/2 N2 (g) + O2 (g) →NO2 (g) B) N2 (g) + 2O2 (g) → N2O4 (g) C) N2 (g) + 2 O2 (g) →2NO2 (g) D) NO(g) + 1/2 O2 (g) → NO2 (g)

1/2 N2 (g) + O2 (g) → NO2 (g)

A 5.00 L vessel contains 2.00 moles of helium and 3.00 moles of hydrogen at a pressure of 10.0 atm. Maintaining a constant temperature, an additional 3.00 moles of hydrogen are added. What is the partial pressure of hydrogen gas in the vessel at the end? (Assume that the gases behave ideally) A) 6.00 atm B) 10.0 atm C) 12.0 atm D) 20.0 atm

12.0 atm

At 17°C, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO3(s), NaBr(s), Cu(s), or I2(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mm Hg. All four vessels are heated to 127°C and allowed to reach a constant pressure. At 127°C, the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation? A) NaHCO3 (s) → Na (s) + HCO3 (s) B) NaHCO3 (s) → NaH (s) + CO3 (s) C) 2NaHCO3 (s) → Na2CO3 (s) + CO2 (g) +H2O (g) D) 2NaHCO3 (s) + N2 (g) → 2NaNO3 (s) +C2H2 (g)

2NaHCO3 (s) → Na2CO3 (s) + CO2 (g) + H2O (g)

2C2H6 (g) + 7O2 (g) →6H2O (g) + 4CO2 (g) How many molecules of H20(g) will result if 1 x 10^23 molecules of C2H6 completely react with excess oxygen? A) 1 x 10^23 molecules B) 3 x 10^23 molecules C) 4 x 10^23 molecules D) 6 x 10^23 molecules

3 x 10^23 molecules

CH3OH (g) → CO (g) + 2H2 (g) △H = 91c kJ/mol The reaction represented above goes essentially to completion. The reaction takes place in a rigid, insulated vessel that is initially at 600 K. A sample of CH3OH (g) is placed in the previously evacuated vessel with a pressure of P1 at 600 K. What is the final pressure in the vessel after the reaction is complete and the contents of the vessel are returned to 600 K A) P1/9 B) P1/3 C) P1 D) 3P1

3P1

CH4 (g) + 4Cl2 (g) → CCl4 (g) + 4HCl (g) △H= -434 kJ Based on the above reaction, what energy change occurs when 1.2 moles of methane (CH4) reacts? A) 5.2 x 10^5 J are released B) 5.2 x 10^5 J are absorbed C) 3.6 x 10^5 J are released D) 3.6 x 10^5 J are absorbed E) 4.4 x 10^J are released

5.2 x 10^5 J are released

A hot iron ball is dropped into a 200. g sample of water initially at 50 ℃. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature fo the water? (The specific heat of water is 4.2 J / (g ℃).) A) 40 ℃ B) 51 ℃ C) 60 ℃ D) 70 ℃

60°C

Reaction A: 4HCl (g) + O2 (g) ⇄ 2Cl2 (g) + 2H2O (g) Reaction B: N2O4 (g) ⇄ 2NO2 (g) Reaction C: H2 (g) + I2 (g) ⇄ 2 HI Reaction D: 2NH3 (g) ⇄ N2(g) + 3H2 (g) The reactions represented above are carried out in sealed, rigid containers and allow to reach equilibrium. If the volume of each container is reduced from 1.0 L to 0.5 L at constant temp, for which of the reactions will the amount of product(s) be increased? A) Reaction A B) Reaction B C) Reaction C D) Reaction D

A) Reaction A

Step 1: Cl (g) + O3 (g) ---> ClO (g) + O2(g) Step 2: ClO (g) + O (g) ---> Cl (g) + O2 (g) A proposed mechanism for destruction of ozone gas in the stratosphere is represented above. Which of the following is evidence that the mechanism is occuring? A) The presence of Cl (g) increases the rate of the overal rxn B) The presence of Cl (g) decreases the rate of the overall rxn C) The presence of Cl (g) increases the equilibrium constant of the overall rxn D) The presence of Cl (g) decreases the equilibrium constant of the overall rxn

A) The presence of Cl (g) increases the rate of the overal rxn

Given the equation S(s) + O2 →SO2 (g), △H= -296 kJ, which of the following statement(s) is (are) true I. The reaction is exothermic II. When .500 mole sulfur is reacted, 148 kJ of energy is released III. When 32.0 g of sulfur are burned, 2.96 x 10^5 J of energy is released A) All are true B) None is true C) I and II are true D) I and III are true E) only II is true

All are true

COCl2 (g) ⇄ CO (g) + Cl2 (g) COCl2 (g) decomposes according to the equation above. When pure COCl 2(g) is injected into a rigid, previously evacuated flask at 690 K, the toal pressure in the flask is 1.2 atm. What is the value of Kp for the reaction at 690 K? A) 0.040 B) 0.050 C) 0.80 D) 1.0

B) 0.050

N2O4 (g) <---> 2NO2 (g) Kp=2.0 at 70C colorless brown A mixutre of NO2 (g) and N2O4 (g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above If PressN2O4 is 1.33atm when the system is at equilibrium at 70C, which is the PressNO2? A) 0.44 atm B) 2.0 atm C) 2.3 atm D) 4.0 atm

B) 2.0 atm

X + O3 ---> XO + O2 XO + O3 ---> X + 2 O2 2 O3 ---> 3 O2 The proposed mechanism can be written in a more general form, as shown above. Species other than Cl can also decompose O3 through the same mechanism. Which of the following chemical species is most likely to decompose O3 in the upper atmosphere through the above mechanism? A) He B) Br C) N2 D) O2

B) Br

H2 (g) + I2 (g) ⇄ 2HI (g) At 450°C, 2.0 moles each of H2(g), I2(g), and HI(g) are combined in a 1.0L rigid container. The value of Kc at 450°C is 50. Which of the following will occur as the system moves toward equilibrium? A) More H2 (g) and I2 (g) will form B) More HI (g) will form C) The total pressure will decrease D) No net rxn will occur, bc the number of molecules is the same on both sides of the equation

B) More HI (g) will form

2 NO2 (g) + F2 (g) ---> 2 NO2F (g) The rate law for the rxn represented above is rate=k[NO2][F2]. Which of the following could be the first elementary step of a twp-step mechanism for the rxn if the first step is slow and the second step is fast? A) F2 (g) ---> 2F (g) B) NO2 (g) + F2 (g) ---> NO2F (g) + F (g) C) NO2 (g) + F (g) ---> NO2F (g) D) 2NO2 (g) + F2 (g) ---> NO2F (g)

B) NO2 (g) + F2 (g) ---> NO2F (g) + F (g)

NO2 (g) + CO (g) ---> NO (g) + CO2(g) The rxn btwn NO2 (g) and CO (g) is represented above. The elementary steps of a proposed rxn mechanism are represented below step 1: 2NO2 (g) ---> NO (g) + NO3 (g) (slow) step 2: NO3 (g) + CO (g) --> NO2 (g) + CO2(g) which of the following is the rate law for the overall rxn that is consistent with the proposed mechanism? A) Rate=k[NO2][CO} B) Rate=k[NO2]^2 C) Rate=k[NO3][CO] D) Rate=k[NO2][NO3][CO]

B) Rate=k[NO2]^2

2H2O2 (aq) --> 2H2O (l) + O2 (g) △H = -196 kJ/mol The decomposition of H2O2 (aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2 (aq) at a constant temperature of 300K and recorded the concentration of H2O2 as a function of time. The results are given in the table below Time(s) [H2O2] 0 2.7 200. 2.1 400. 1.7 600. 1.4 Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined A) the reaction must be first order bc there is only one reactant species B) The rxn is first order if the plot of ln[H2O2] vs time is a straight line C) the rxn is first order if the plot of 1/[H2O2] vs time is a straight line D) The rxn is second order bc 2 is the coefficient of H2O2 in the chemical equation

B) The rxn is first order if the plot of ln [H2O2] vs time is a straight line

2XY (g) ⇄ X2 (g) + Y2(g) Kp=230 A certain gas, XY (g), decomposes as represented by the equation above. A sample of each of the three gases is put in a previously evacuated container. The inital partial pressure of the gases are shown in the table below gas Initial partial pressure (atm) XY 0.010 X2 0.20 Y2 2.0 The temperature of the rxn mixture is held constant. In which direction will the rxn proceed? A) The rxn will form more products B) The rxn will form more reactant C) The mixture is at equilibrium, so there will be no change D) it cannot be determined unless the volume of the container is known

B) The rxn will form more reactant

NO (g) + NO3 (g) ---> 2NO2 (g) rate=k[NO][NO3] The rxn represented above occurs in a single step that involves the collision btwn a particel of NO and a particle of NO3. A scientist correctly calculates the rate of collisions btwn NO and NO3 that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy? A) The energy of collisions btwn two reactant particles is frequently absorbed by collision with a third particle B) The two reactant particles must collide w a particular orientation to react C) The activation energy for a reaction is dependent on the [ ] of the reactant particles D) The activation energy for a rxn is dependent on the temp

B) The two reactant particles must collide w a particular orientation to react

CO (g) + 2 H2 (g) ⇄ CH3OH (g) △H<0 The synthesis of CH3OH(g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5 A 1.0 mol sample of CO (g) and a 1.0 mol sample of H2 (g) are pumped into a rigid, previously evacuated 2.0 L reaction vesssel at 483 K. Which of the following is true at equilibrium? A) [H2] = 2[CO] B) [H2] < [CO] C) [CO] = [CH3OH] < [H2] D) [CO] = [CH3OH] = H2

B) [H2] < [CO]

C2H4 (g) + H2 (g) ---> C2H6 (g) which of the following will most likely increase the rate of the reaction represented above? A) decreasing the temp of the rxn system B) adding a heterogeneous catalyst to the rxn system C) increasing the volume of the rxn vessel using a piston D) removing some H2 (g) from the rxn system

B) adding a heterogeneous catalyst to the rxn system

Consider the rxn represented by the equation 2X + 2Z ---> X2Z2. During a rxn in which a large excess of reactant X was present, the concentration of reactant Z was monitored over time. A plot of the ln of [Z] vs time is a straight line with a negative slope. The order of the reaction with respect to reactant Z is A) zero order B) first order C) second order D) third order

B) first order

CO (g) + 2 H2 (g) ⇄ CH3OH (g) △H<0 The synthesis of CH3OH(g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5 A mixture of CO (g) and H2 (g) is pumped into a previously evacuated 2.0 L reaction vessel. The total pressure of the reaction system is 1.2 atm at equilibrium. What will be the total pressure of the system if the volume o the reaction vessel is reduced to 1.0 L at constant temperature? A) Less than 1.2 atm B) Greater than 1.2 atm but less than 2.4 atm C) 2.4 atm D) Greater than 2.4 atm

B) greater than 1.2 atm but less than 2.4 atm

CaCO3 (s) ⇄ CaO (s) + CO2 (g) △H = 178 kJ/mol The rxn system represented above is at equilibrium. Which of the following will decrease the amount of CaO(s) in the system A) Increasing the volume of the rxn vessel at a constant temp B) Lowering the temp of the system C) Removing some CO2 (g) at constant temp D) Removing some CaCO3 (s) at constant temp

B) lowering the temp of the system

What is the value o the enthalpy change per mole of HCL (g) produced? A) -93 kJ B) -121 kJ C) -186 kJ D) -242 kJ

C) -186 kJ

X2 + Y2→X2Y2 rate = k[X2] a reaction and its experimentally determined rate law are represented above. A chemist propose two different possible mechanism for the reaction, which are given below Mechanism 1 X2 → 2X (slow) X + Y2 → XY2 (fast) X + XY2 → X2Y2 (fast) Mechanism 2 X2 →2X (slow) X + Y2 →XY + Y (fast) X + XY → X2Y (fast) X2Y + Y → X2Y2 (fast) Based on the information above which of the following is true? A) only mechanism 1 is consistent with the rate law B) Only mechanism 2 is consistent with the rate law C) Both mechanism 1 and mechanism 2 are consistent with the rate law D) neither mechanism 1 nor mechanism 2 is consistent with the rate law

C) Both mechanism 1 and mechanism 2 are consistent with the rate law

CO (g) + 2 H2 (g) ⇄ CH3OH (g) △H<0 The synthesis of CH3OH(g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5 Which of the follow explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased to 650 K? A) Kc will increase because the activation energy of the forward reaction increases more than that of the reverse reaction B) Kc will increase because there are more reactant molecules than product molecules C) Kc will decrease because the reaction is exothermic D) Kc is constant and will not change

C) Kc will decrease because the reaction is exothermic

2H2O2 (aq) --> 2H2O (l) + O2 (g) △H = -196 kJ/mol The decomposition of H2O2 (aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2 (aq) at a constant temperature of 300K and recorded the concentration of H2O2 as a function of time. The results are given in the table below Time(s) [H2O2] 0 2.7 200. 2.1 400. 1.7 600. 1.4 Which of the following identifies the element(s) being oxidized and reduced in the reaction? A)Hydrogen is oxidized and oxygen is reduced B) Oxygen is oxidized and hydrogen is reduced C) Oxygen is both oxidized and reduced D) No elements are oxidized or reduced; the reaction is not a redox rxn

C) Oxygen is both oxidized and reduced

CO (g) + 2 H2 (g) ⇄ CH3OH (g) △H<0 The synthesis of CH3OH(g) from CO (g) and H2 (g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5 Which of the following statements is true about bond energies in this reaction? A)The energy absorbed as the bonds in the reactants are broken is greater than the energy released as the bonds in the product are formed B) The energy released as the bonds in the reactants are broken is greater than the energy absorbed as the bonds in the product are formed C) The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed D) The energy released as the bonds in the reactants are broken is less than the energy absorbed as the bonds in the product are formed

C) The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed

PCl3 (g) + Cl2 (g) ⇄ PCl5 (g) Kc = 6.5 At a certain point in time, a 1.00L rigid rxn vessel contains 1.5 mol of PCl3 (g), 1.0 mol of Cl2 (g), and 2.5 mol of PCl5 (g). Which of the following describes how the measured pressure in the rxn vessel will change and why it will change that way as the rxn system approaches equilibrium at constant temp? A) the pressure will increase bc Q < Kc B) the pressure will increase bc Q > Kc C) the pressure will decrease bc Q < Kc D) the pressure will decrease bc Q > Kc

C) the pressure will decrease bc Q < Kc

A kinetics experiment is set up to collect the gas that is generated when a sample of chalk, consisting primarily of solid CaCO3, is added to a solution of ethanoic acid, CH3COOH. The rate of rxn btwn CaCO3 and CH3COOH is determined by measuring the volume of gas generated at 25C and 1 atm as a function of time. Which of the following experimental conditions is most likely to increase the rate of gas production? A) Decreasing the volume of ethanoic acid solution used in the experiment B) Decreasing the concentration of the ethanoic acid solution used the experiment C) Decreasing the temp at which the experiment is performed D) Decreasing the particle size of the CaCO3 by grinding it into a fine powder

D) Decreasing the particle size of the CaCO3 by grinding it into a fine powder

N2O4 (g) <---> 2NO2 (g) Kp=2.0 at 70C colorless brown A mixture of NO2 (g) and N2O4 (g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above which of the following best predicts how the partial pressures of the reacting species will be affected if a small amount of Ar (g) is added to the equilibrium mixture at constant volume? A) PNO2 will decrease and PN2O4 will increase B) PNO2 will increase and PN2O4 will decrease C) Both PNO2 and PN2O4 will decrease D) No change will take place

D) No change will take place

N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g) Kc = 3.7 × 108 delta H < 0 NH3 (g) was synthesized at 200C in the presence of a powdered Os(s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3 (g) in the mixture after equilibrium is reestablished? A) replacing the powdered Os(s) with a solid cube of Os(s) of the same total mass B) increasing the temp of the system to 250C at constant pressure C) removing some H2 (g) D) adding some N2 (g)

D) adding some N2 (g)

Which of the following best helps explain why an increase in temp increases the rate of a chemical rxn? A) at higher temps, rxns have a lower activation energy B) at higher temps, rxns have a higher activation energy C) at higher temps, every collision results in the formation of product D) at higher temps, high-energy collisions happen more frequently

D) at higher temps, high-energy collisions happen more frequently

3O2(g) <---> 2O3(g) Kc = 1.8 x 10^-56 at 570 K for the system represented above, [O2] and [O3] initially are 0.150 mol/L and 2.5 mol/L respectively. Which of the following best predicts what will occur as the system approaches equilibrium at 570 K? A) the amount of O3 (g) will increase, because Q<Kc B) the amount of O3 (g) will decrease, because Q<Kc C) The amount of O3(g) will increase, because Q>Kc D) the amount of O3 will decrease, because Q>Kc

D) the amount of O3 will decrease, because Q>Kc

2NO (g) + O2 (g) --> 2NO2 (g) Consider the following rxn mechanism for the rxn represented above. Step 1 : 2 NO ⇄ N2O2 (fast reversible) Step 2: N2O2 + O2 ---> 2NO2 (slow) Which of the following statements is true? A) step 1 represents a unimolecular reaction B) Increasing the concentration of NO will decrease the overall rate of the reaction C) Raising the temp will have no effect on the numerical value of the rate constant D) the rate law that is consistent with mechansim is rate = k[NO]^2[O2]

D) the rate law that is consistent with mechansim is rate = k[NO]^2[O2]

Which of the following statements identifies the greatest single reason that the value of Kp for the overall rxn at 298 K has such a large magnitude? A) the activation energy for step 1 of the mechanism is large and positive B) the activation energy for step 2 of the mechanism is small and positive C) the value of △S for the overall rxn is small and positive D) the value of △H for the overall rxn is large and negative

D) the value of △H for the overall rxn is large and negative

N2O4 (g) <---> 2NO2 (g) Kp=2.0 at 70C colorless brown A mixture of NO2 (g) and N2O4 (g) is placed in a glass tube and allowed to reach equilibrium at 70C, as represented above which of the following statements about △H for the rxn is correct? A) △H<0 bc energy is released when the N-N bond breaks B) △H<0 bc energy is required to break the N-N bond C) △H>0 bc energy is released when the N-N bond breaks D) △H>0 bc energy is required to break the N-N bond

D) △H>0 bc energy is required to break the N-N bond

The sample below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4 The best explanation for the lower pressure in container 4 is that SO2 molecules A) have a larger average speed than the other three gases B) occupy a larger portion of the container volume than the other three gases C) Have stronger inter molecular attractions D) contain π bonds, while the other gases contain only σ bonds

Have stronger inter molecular attractions than the other three gases

In the lab, you mix two solutions (each originally at the same temperature) and the temperature of the resulting solution decreases. Which of the following is true? A) the chemical reaction is releasing energy B) the energy released is equal to s x m x △T C) the chemical reaction is absorbing energy D) the chemical reaction is exothermic E) more than one of these

The chemical reaction is absorbing energy

At 17°C, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO3(s), NaBr(s), Cu(s), or I2(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mm Hg. All four vessels are heated to 127°C and allowed to reach a constant pressure. At 127°C, the entire sample of is I2 observed to have vaporized. How does the mass of vessel 5 at 127°C compare to its mass at 27°C? A) The mass is less, since I2 is in the vapor phase B) The mass is the same, since the number of each atom in the vessel is constant C) The mass is greater, since the I2 will react with N2 to form NI3, which has a greater molar mass D) The mass is greater, since the pressureis greater and the particles have a higher average kinetic energy

The mass is the same, since the number of each type of atom in the vessel is constant.