Q&A Hero

Q: Carbon dating may be used to date (once living) materials that are between 100 and 40,000 years old. The half-life of the first-order decay of carbon-14 is 5730 years. What percentage of carbon-14 remains in a sample after 40,000 years.

Q: Termolecular elementary steps are rare. Why?

Q: Elementary steps in a reaction mechanism often include reaction ________. These (usually) short-lived species, which are at one point produced and then later consumed, do not appear in the overall chemical reaction.

Q: Radioactive isotopes decay by ________-order kinetics.

Q: The pre-exponential, A, in the Arrhenius equation is called the ________ factor.

Q: The ________ of an elementary step is defined as the number of reactant molecules that come together in the reaction.

Q: If a catalyst is present in a different phase from the reactants and products, it is referred to as a(n) ________ catalyst.

Q: For the overall reaction 2A + B C which of the following mechanisms yields the correct overall chemical equation and is consistent with the rate equation below? rate = k[A]2[B] A.A + B I (fast) I + A C (slow) B.A + B I (slow) I + B C (fast) C.2A I (slow) B + I C (fast) D.A + B I (slow) I + A C (fast) E.A + 2B I (fast) I + B C + B (slow)

Q: For the overall reaction A + 2B C which of the following mechanisms yields the correct overall chemical equation and is consistent with the rate equation below? rate = k[A][B] A.A + B I (fast) I + A C (slow) B.A + B I (slow) I + B C (fast) C.2B I (slow) A + I C (fast) D.2B I (fast) I + A C (slow) E.A + 2B I (fast) I + B C + B (slow)

Q: Nitrogen dioxide reacts with carbon monoxide to produce nitrogen monoxide and carbon dioxide.NO2(g) + CO(g) NO(g) + CO2(g)A proposed mechanism for this reaction is2 NO2(g) NO3(g) + NO(g) (fast, equilibrium)NO3(g) + CO(g) NO2(g) + CO2(g) (slow)What is a rate law that is consistent with the proposed mechanism?A.rate = k[NO2]2[CO] [NO]-1B.rate = k[NO2]2[CO]C.rate = k[NO2][CO]D.rate = k[NO3][CO]E.rate = k[NO2]2

Q: The mechanism of a chemical reaction is given below.(CH3)3CCl (CH3)3C+ + Cl- (slow)(CH3)3C+ + OH- (CH3)3COH (fast)Which of the following statements concerning the reaction is/are CORRECT?1/ The overall balanced reaction is: (CH3)3CCl + OH- (CH3)3COH + Cl-2/ Hydroxide ion is a reaction intermediate.3/ The following rate law is consistent with the mechanism: rate = k[(CH3)3CCl]OH-].A.1 onlyB.2 onlyC.3 onlyD.1 and 3E.1, 2, and 3

Q: The elementary steps for the catalyzed decomposition of dinitrogen monoxide are shown below. N2O(g) + NO(g) N2(g) + NO2(g) NO2(g) NO(g) + 1/2 O2(g) Which of the following statements is/are CORRECT? 1/ The overall balanced reaction is N2O(g) N2(g) + 1/2 O2(g). 2/ NO2(g) is a catalyst for the reaction. 3/ NO(g) is a reaction intermediate. A.1 only B.2 only C.3 only D.1 and 3 E.1, 2, and 3

Q: The effect of adding a catalyst to a reaction is to A.increase the number of collisions between reactants. B.lower the activation energy of a reaction. C.increase the equilibrium constant of a reaction. D.decrease the yield of the products. E.increase the enthalpy change of a reaction.

Q: The rate constant at 366 K for a first-order reaction is 7.7 10-3 s-1 and the activation energy is 15.9 kJ/mol. What is the value of the frequency factor, A, in the Arrhenius equation? (R = 8.314 J/Kmol)A.0.0047 s-1B.0.70 s-1C.0.93 s-1D.1.1 s-1E.1.4 s-1

Q: For a given reaction, the activation energy is 63.9 kJ/mol. If the reaction rate constant is 4.1 10-3 M-1s-1 at 32.0 C, what is the reaction rate constant at -5.0 C? (R = 8.314 J/Kmol)A.1.2 10-3 M-1s-1B.1.4 10-6 M-1s-1C.1.3 10-4 M-1s-1D.4.0 10-3 M-1s-1E.1.3 10-1 M-1s-1

Q: For a given reaction, the rate constant doubles when the temperature is increased from 45.0 C to 73.0 C. What is the activation energy for this reaction? (R = 8.314 J/Kmol) A.0.676 kJ/mol B.9.85 kJ/mol C.16.1 kJ/mol D.22.7 kJ/mol E.65.4 kJ/mol

Q: Calculate the activation energy, Ea, forN2O5(g) 2 NO2(g) + 1/2 O2(g)given k (at 45.0 C) = 5.79 10-4 s-1 and k (at 60.0 C) = 3.83 10-3 s-1. (R = 8.314 J/Kmol)A.0.256 kJ/molB.2.83 kJ/molC.31.1 kJ/molD.111 kJ/molE.389 kJ/mol

Q: For a chemical reaction, the activation energy for the forward reaction is +181 kJ and the activation energy for the backward reaction is +62 kJ. What is the overall energy change for the forward reaction?A.-119 kJB.-62 kJC.+119 kJD.+181 kJE.+243 kJ

Q: Molecules must overcome a barrier called the activation energy if they are to react. The highest energy point reached during the progress of a reaction is called the ____. A.rate determining step B.transition state C.half-life D.elementary step E.intermediate state

Q: The Arrhenius equation, , relates the rate constant of reaction and temperature. A plot of ____ versus 1/T will yield a straight line with a slope of -Ea/R.A.k2/k1B.-EaC.ln(k)D.E.1/RT

Q: In general, as temperature increases, the rate of a chemical reaction A.decreases due to fewer collisions with proper molecular orientation. B.increases for exothermic reactions, but decreases for endothermic reactions. C.increases due to a greater number of effective collisions. D.remains unchanged. E.decreases due to an increase in the activation energy.

Q: According to collision theory, which condition(s) must be met in order for molecules to react? 1/ The reacting molecules must collide with sufficient energy to initiate the process of breaking and forming bonds. 2/ A catalyst must be in contact with the reacting molecules for a reaction to occur. 3/ The reacting molecules must collide with an orientation that can lead to rearrangement of the atoms. A.1 only B.2 only C.3 only D.1 and 2 E.1 and 3

Q: For the zero-order reaction below, a graph of ____ versus time will generate a straight line. A B + C rate = k[A]0 A.[A]t B. C.ln[A]t D. E.

Q: For the second-order reaction below, the initial concentration of reactant A is 0.24 M. If the rate constant for the reaction is 1.5 10-2 M-1s-1, what is the concentration of A after 265 seconds?2A B + C rate = k[A]2A.0.12 MB.0.19 MC.0.95 MD.4.0 ME.5.2 M

Q: For the second-order reaction below, the rate constant of the reaction is 9.4 10-3 M-1s-1. How long (in seconds) is required to decrease the concentration of A from 2.16 M to 0.40 M?2A B rate = k[A]2A.2.0 101 sB.7.8 101 sC.1.8 102 sD.1.9 102 sE.2.2 102 s

Q: What is the half-life of a first-order reaction if it takes 4.4 10-2 seconds for the concentration to decrease from 0.50 M to 0.20 M?A.2.5 10-2 sB.3.3 10-2 sC.1.6 sD.21 sE.27 s

Q: The decomposition of phosphine, PH3, follows first-order kinetics. 4 PH3(g) P4(g) + 6 H2(g) The half-life for the reaction at 550 C is 81.3 seconds. What percentage of phosphine remains after 195 seconds? A.2.2% B.9.8% C.19% D.42% E.58%

Q: The decomposition of formic acid follows first-order kinetics. HCO2H(g) CO2(g) + H2(g) The half-life for the reaction at 550 C is 24 seconds. How many seconds does it take for the formic acid concentration to decrease by 87.5%? A.24 s B.36 s C.48 s D.72 s E.96 s

Q: Hydrogen peroxide decomposes into water and oxygen in a first-order process. H2O2(aq) H2O() + 1/2 O2(g) At 20.0 C, the half-life for the reaction is 3.92 104 seconds. If the initial concentration of hydrogen peroxide is 0.52 M, what is the concentration after 7.00 days? A.1.2 10-5 M B.0.034 M C.0.074 M D.0.22 M E.0.52 M

Q: The reaction A B follows first-order kinetics with a half-life of 21.7 hours. If the concentration of A is 0.023 M after 48.0 hours, what is the initial concentration of A? A.0.0050 M B.0.051 M C.0.51 M D.0.11 M E.2.0 102 M

Q: For a reaction, A B + C, which of the following equations corresponds to the integrated expression for a zero-order decomposition reaction? A. B. C. D. E.

Q: For the first-order decomposition of N2O5 at a high temperature, determine the rate constant if the N2O5 concentration decreases from 1.04 M to 0.62 M in 375 seconds.A.5.99 10-4 s-1B.1.59 10-3 s-1C.1.74 10-3 s-1D.1.38 10-3 s-1E.1.94 102 s-1

Q: What is the half-life of a first-order reaction if the rate constant is 6.2 10-3 s-1?A.8.9 10-3 sB.0.097 sC.5.77 sD.1.0 102 sE.1.6 102 s

Q: The rate constant of a first-order decomposition reaction is 0.0147 s-1. If the initial concentration of reactant is 0.178 M, what is the concentration of reactant after 30.0 seconds?A.8.72 105 MB.0.0645 MC.0.115 MD.0.0785 ME.0.643 M

Q: For a reaction, A B + C, which of the following equations corresponds to the integrated expression for a second-order decomposition reaction? A. B. C. D. E.

Q: A student analyzed a first-order reaction and obtained the graph below. Unfortunately, the student forgot to label the axes. What are the correct labels for the x and y axes? A.x axis = time, y axis = ln[A] B.x axis = ln[time], y axis = [A] C.x axis = ln[time], y axis = [A] D.x axis = time, y axis = 1/[A] E.x axis = 1/time, y axis = 1/[A]

Q: If an egg's shell is carefully dissolved using an acid, the egg white and yolk will remain intact inside a membrane. If the egg is then placed in distilled water, it will slowly expand until it bursts. Why?

Q: A solution in which there is more dissolved solute than in a saturated solution is known as a(n) ________ solution.

Q: The following equation is known as ________ law: .

Q: If one of the factors determining the equilibrium of a system is changed, the system adjusts to counteract that change. This is known as ________ principle.

Q: ________ are colloidal dispersions of one liquid in another liquid.

Q: A surfactant used for cleaning is called a(n) ________.

Q: Aqueous colloidal solutions can be classified as ________ (water-fearing), or hydrophilic (water-loving).

Q: Because ________ particles are relatively large (say, 1000 nm in diameter) they scatter visible light, making the mixtures containing these particles appear cloudy. This scattering is known as the Tyndall effect.

Q: A(n) ____ is a colloidal dispersion of a solid in a liquid. A.gel B.emulsion C.aerosol D.foam E.sol

Q: A(n) ____ is a colloidal dispersion of a liquid in a solid. A.gel B.emulsion C.aerosol D.foam E.sol

Q: Clouds and fog are colloidal dispersions that contain a liquid dispersed in a gaseous medium. This type of colloid is called a(n) ____. A.emulsion B.aerosol C.foam D.sol E.gel

Q: All of the following are colloidal dispersions EXCEPT ____. A.marshmallow B.white wine C.milk D.whipped cream E.cheese

Q: A solution is prepared by dissolving 5.88 g of an unknown nonelectrolyte in enough water to make 0.355 L of solution. The osmotic pressure of the solution is 1.21 atm at 27 C. What is the molar mass of the solute? (R = 0.08206 Latm/molK) A.0.00297 g/mol B.30.3 g/mol C.42.5 g/mol D.175 g/mol E.337 g/mol

Q: The osmotic pressure of blood is 7.65 atm at 37 C. What mass of glucose (C6H12O6, molar mass = 180.2 g/mol) is needed to prepare 2.25 L of solution for intravenous injection? The osmotic pressure of the glucose solution must equal the osmotic pressure of blood. (R = 0.08206 Latm/molK) A.0.676 g B.0.698 g C.5.67 g D.122 g E.1.02 103 g

Q: At 25 C, what is the osmotic pressure of a homogeneous solution consisting of 21.0 g urea (CON2H4) diluted with water to 2.50 L? (R = 0.08206 Latm/molK) A.0.205 atm B.3.42 atm C.8.55 atm D.12.3 atm E.147 atm

Q: Which of the following statements concerning osmosis is/are CORRECT? 1/ Osmosis involves the movement of ions through a semipermeable membrane until the charges on both sides of the membrane are equal. 2/ Solvents move from regions of low solute concentration to regions of higher solute concentration. 3/ Osmotic pressure is a colligative property. A.1 only B.2 only C.3 only D.2 and 3 E.1, 2, and 3

Q: What concentration unit is used in the calculation of osmotic pressure for a dilute solution? A.molality B.weight percent C.mass fraction D.mole fraction E.molarity

Q: The freezing point depression constant of water is -1.86 C/m. If 7.50 g NaCl is dissolved in 45.0 g H2O, the freezing point is changed by -9.71 C. Calculate the van't Hoff factor for NaCl.A.1.00B.1.54C.1.67D.1.83E.1.91

Q: What mass of Na2SO4 must be dissolved in 100.0 grams of water to lower the freezing point by 2.50 C? The freezing point depression constant, Kfp, of water is -1.86 C/m. Assume the van't Hoff factor for Na2SO4 is 2.85.A.3.77 gB.6.36 gC.6.70 gD.11.3 gE.19.1 g

Q: What is the boiling point of a solution containing 0.852 g naphthalene(C10H8, molar mass = 128.2 g/mol) dissolved in 14.0 g benzene? The boiling point of pure benzene is 80.10 C and the boiling point elevation constant, Kbp, is 2.53 C/m. A.78.70 C B.80.25 C C.81.30 C D.82.50 C E.85.43 C

Q: What is the molar mass of a nonpolar molecular compound if 3.37 grams dissolved in 45.3 grams benzene begins to freeze at -0.04 C? The freezing point of pure benzene is 5.50 C and the freezing point depression constant, Kfp, is -5.12 C/m.A.35.1 g/molB.68.8 g/molC.80.5 g/molD.116 g/molE.359 g/mol

Q: What is the freezing point of a solution containing 2.80 grams benzene (molar mass = 78.11 g/mol) dissolved in 43.0 grams paradichlorobenzene (molar mass = 147.0 g/mol)? The freezing point of pure paradichlorobenzene is 53.0 C and the freezing point depression constant, Kfp, is -7.10 C/m.A.46.7 CB.47.1 CC.58.9 CD.52.6 CE.58.9 C

Q: The freezing point depression constant for water is -1.86 C/m. At what temperature will a solution containing 7.75 g KCl and 45.0 g H2O begin to freeze? Assume that no ion-pairing occurs between K+ and Cl-.A.-8.59 CB.-4.30 CC.-2.15 CD.-1.59 CE.-0.51 C

Q: Assuming ideal behavior, which of the following aqueous solutions should have the highest boiling point? A.1.00 m LiBr B.0.75 m K2SO4 C.0.50 m Ca(NO3)2 D.0.75 m NaCl E.1.25 m C6H12O6

Q: Assuming ideal behavior, which of the following solutions should have the lowest freezing point? A.pure H2O B.1.0 m MgCl2(aq) C.1.0 m RbBr(aq) D.1.0 m NH3(aq) E.1.0 m C6H12O6(aq)

Q: What mass of ethylene glycol, when mixed with 225 g H2O, will reduce the equilibrium vapor pressure of H2O from 1.00 atm to 0.800 atm at 100 C? The molar masses of water and ethylene glycol are 18.02 g/mol and 62.07 g/mol, respectively. Assume ideal behavior for the solution. A.15.6 g B.49.9 g C.194 g D.969 g E.3.10 103 g

Q: The vapor pressure of pure water at 15 C is 12.8 mm Hg. What is the equilibrium vapor pressure of water above a mixture of 72.0 g ethanol (CH3CH2OH, molar mass = 46.07 g/mol) and 22.0 g water? A.2.84 mm Hg B.5.61 mm Hg C.7.19 mm Hg D.10.0 mm Hg E.12.8 mm Hg

Q: What is the equilibrium partial pressure of water vapor above a mixture of 37.5 g H2O and 62.5 g HOCH2CH2OH at 55 C. The partial pressure of pure water at 55.0 C is 118.0 mm Hg. Assume ideal behavior for the solution. A.3.54 mm Hg B.31.7 mm Hg C.38.5 mm Hg D.79.5 mm Hg E.175 mm Hg

Q: Ideally, colligative properties depend only on the A.relative numbers of solute and solvent particles in a solution. B.molar masses of the solute particles in a solution. C.density of a solution. D.hydrated radii of the molecules or ions dissolved in a solution. E.partial pressure of the gases above the surface of a solution.

Q: The Henry's law constant for O2 in water at 25 C is 1.3 10-3 mol/kgbar. What partial pressure of O2 (in atm) is necessary to achieve an equilibrium concentration of 2.9 10-3 mol/kg O2? (1 atm = 0.9869 bar)A.0.44 atmB.0.45 atmC.2.1 atmD.2.3 atmE.3.8 atm

Q: Which action(s) will decrease the equilibrium concentration of an inert gas (such as N2) in water? 1/ decreasing the temperature of the water 2/ increasing the volume of water 3/ decreasing the pressure of the gas above the liquid A.1 only B.2 only C.3 only D.1 and 3 E.1, 2, and 3

Q: The Henry's law constant for N2 in water at 25 C is 6.0 10-4 mol/kgbar. What is the equilibrium concentration of N2 in water when the partial pressure of N2 is 586 mm Hg? (760 mm Hg = 1 atm = 0.9869 bar)A.1.4 10-9 MB.1.8 10-5 MC.4.6 10-4 MD.7.7 10-4 ME.7.9 10-4 M

Q: Which of the following statements is INCORRECT? A.The solubility of a gas in water decreases with increasing temperature. B.The solubility of a gas in water is proportional to the partial pressure of the gas above the water. C.The dissolution of a gas in water is usually an exothermic process. D.The relationship between the solubility of a gas and its partial pressure is known as Henry's law. E.The solubility of a gas in water is inversely proportional to the molar mass of the gas.

Q: The standard enthalpy of formation of NaOH(s) is -425.9 kJ/mol and the standard enthalpy of formation of NaOH(aq, 1 m) is -469.2 kJ/mol. Determine the heat of solution of NaOH. Will the solution temperature increase or decrease when NaOH is dissolved in water?A.-43.3 kJ/mol; increaseB.+43.3 kJ/mol; increaseC.-43.3 kJ/mol; decreaseD.+895.1 kJ/mol; increaseE.-895.1 kJ/mol; decrease

Q: The standard enthalpy of formation of RbF(s) is -557.7 kJ/mol and the standard enthalpy of formation of RbF(aq, 1 m) is -583.8 kJ/mol.Which of the following statements concerning the dissolution of RbF in water is/are CORRECT?1/ The dissolution of RbF(s) in water is endothermic.2/ The standard enthalpy of solution of RbF(s) is +26.1 kJ/mol.3/ The dissolution of RbF(s) in water results in an increase in the solution's temperature.A.1 onlyB.2 onlyC.3 onlyD.1 and 2E.1, 2, and 3

Q: Which of the following statements concerning solubility is/are CORRECT? 1/ Ionic compounds composed of Group 1A metal ions and halide ions, such as NaCl, are insoluble in nonpolar solvents. 2/ The solubility of the halogens (Cl2, Br2, and I2) in polar solvents is greater than their solubility in nonpolar solvents. 3/ The solubility of polar molecules, such as sugar, in polar solvents is generally greater than their solubility in nonpolar solvents. A.1 only B.2 only C.3 only D.1 and 3 E.1, 2, and 3

Q: Two nonpolar solvents, such as hexane and carbon tetrachloride, may be miscible even though the enthalpy of mixing of these liquids might be small. A reason that mixing occurs is that mixtures have greater disorder than pure solvents. The tendency toward disorder is a thermodynamic function called ____. A.entropy B.enthalpy C.saturation D.adhesion E.cohesion

Q: Which of the following liquids will be miscible with water in any proportions: ethanol (CH3CH2OH), carbon tetrachloride (CCl4), hexane (C6H14), and/or formic acid (HCO2H)? A.ethanol and carbon tetrachloride B.carbon tetrachloride and hexane C.ethanol and formic acid D.ethanol, carbon tetrachloride, and benzene E.carbon tetrachloride, and formic acid

Q: Which of the following statements is/are CORRECT? 1/ Solubility is defined as the concentration of solute in equilibrium with undissolved solute in a saturated solution. 2/ If two liquids mix to an appreciable extent to form a solution, they are miscible. 3/ If two liquids mix completely in any proportion to form a solution, the resulting solution is supersaturated. A.1 only B.2 only C.3 only D.1 and 2 E.2 and 3

Q: What mass of Zn(NO3)2 must be diluted to a mass of 1.00 kg with H2O to prepare 97 ppm Zn2+(aq)?A.7.8 10-6 gB.7.8 10-3 gC.3.3 10-2 gD.1.3 10-1 gE.2.8 10-1 g

Q: What concentration of silver nitrate (in ppm) is present in 7.1 10-7 M AgNO3(aq)? For very dilute aqueous solutions, you can assume the solution's density is 1.0 g/mL. The molar mass of AgNO3 is 169.9 g/mol.A.0.0071 ppmB.0.12 ppmC.0.71 ppmD.1.7 ppmE.8.3 ppm

Q: A 15 meter by 12 meter pool of water has a depth of 2.2 meters. What mass of silver ion is present in the reservoir if the concentration of silver ion is 0.14 ppm? (1 m3 = 1000 L; assume the density of the solution is 1.00 g/mL)A.5.5 10-4 gB.5.5 10-2 gC.0.55 gD.5.5 gE.55 g

Q: If the concentration of sodium carbonate in water is 12.8 ppm, what is the molarity of Na2CO3(aq)? The molar mass of Na2CO3 is 106.0 g/mol. Assume the density of the solution is 1.00 g/mL.A.8.28 10-6 MB.1.21 10-4 MC.1.36 10-3 MD.0.136 ME.0.121 M

Q: Concentrated sodium hydroxide is 19.4 M and has a density of 1.54 g/mL. What is the molality of concentrated NaOH? A.12.6 m B.19.8 m C.25.4 m D.29.9 m E.50.4 m