2. Which of the following liquids would have the highest viscosity at 25 C? A) CH 3 OCH 3 B) CH 2 Cl 2 C) C 2 H 5 OH D) CH 3 Br E) HOCH 2 CH 2 OH

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1 CHEF124 Mid Term Revision (Trimester 3, 2012/13) 1. Identify the dominant (strongest) type of intermolecular force present in (a) RbCl(s) ionic (b) NH 3 (l) - hydrogen bonding (c) Cl 2 (l) dispersion (d) F 2 (l) dispersion (e) HF(l) - hydrogen bonding (f) SO 2 (l) - dipole-dipole (g) He(l)- dispersion (h) C 2 H 6 (g) dispersion (i) CHCl 3 (l)- dipole-dipole (j) SF 4 (g) - dipole-dipole (k) CF 4 (g) dispersion (l) HCl(g)- dipole-dipole (m) CH 3 OH(l) - hydrogen bonding (n) CH 2 O(g)- dipole-dipole 2. Which of the following liquids would have the highest viscosity at 25 C? A) CH 3 OCH 3 B) CH 2 Cl 2 C) C 2 H 5 OH D) CH 3 Br E) HOCH 2 CH 2 OH 3. For which of the following species are the dispersion forces strongest? A) C 4 H 10 B) C 5 H 12 C) C 6 H 14 D) C 7 H 16 E) C 8 H Arrange the following in order of increasing boiling point: RbCl, CH 3 Cl, CH 3 OH, CH 4. Ans: CH 4 < CH 3 Cl < CH 3 OH < RbCl 5. Vanadium crystallizes in a body-centered cubic lattice, and the length of the edge of a unit cell is 305 pm. What is the density of V? Ans: 5.96 g/cm 3 6. Platinum has a face-centered cubic crystal structure and a density of 21.5 g/cm 3. What is the radius of the platinum atom? Ans: 139 pm 7. The atomic planes in a graphite crystal are separated by 335 pm. At what angle would you find the first-order (n = 1) diffraction of nm X-rays from a graphite crystal? Ans: The vapor pressure of ethanol is 400 mmhg at 63.5 C. Its molar heat of vaporization is 39.3 kj/mol. What is vapor pressure of ethanol, in mmhg, at 34.9 C? Ans: mmhg 9. The normal boiling point of methanol (CH 3 OH) is 64.6 C. Given that the vapor pressure of methanol is 75.0 torr at 15.2 C, calculate the molar enthalpy of vaporization of methanol. Ans: 38.0 kj/mol 1

2 10. Determine the mass percent HCl in a 1.2 M solution of hydrochloric acid with a density of g/ml? Ans: 4.3 % 11. A 20.0 % by mass solution of phosphoric acid (H 3 PO 4 ) in water has a density of g/ml at 20 C. What is the molarity of this solution? Ans: 2.27 M 12. Calculate the percent by mass of potassium nitrate in a solution made from 45.0 g KNO 3 and 295 ml of water. The density of water is g/ml. Ans: 13.3 % 13. What is the molality of a solution that is 3.68 % by mass calcium chloride. Ans: m 14. What is the mass percent CH 3 OH of a m CH 3 OH(aq) solution. Ans: 0.82 % 15. A solution is 40.0% by volume benzene (C 6 H 6 ) in carbon tetrachloride at 20 C. The vapor pressure of pure benzene at this temperature is mmhg and its density is g/cm 3 ; the vapor pressure of pure carbon tetrachloride is mmhg and its density is g/cm 3. If this solution is ideal, its total vapor pressure at 20 C is Ans: mmhg 16. What is the freezing point of a solution that contains 10.0 g of glucose (C 6 H 12 O 6 ) in 100. g of H 2 O? K f for water is 1.86 C/m. Ans: 1.03 C 17. What is the osmotic pressure of a 0.25 M solution of sucrose at 37 C? (R = L atm/k mol) Ans: 6.4 atm 18. What is the boiling point of an aqueous solution of a nonelectrolyte that has an osmotic pressure of atm at 25 C? K b of water is 0.52 C/m. Assume the density of the solution is the same as that of pure water. Ans: C 19. An aqueous dextrose solution having a density of 1.04 g/cm 3 freezes at 1.15 C. Find the osmotic pressure of this solution at 25 C. K f of water is 1.86 C/m; molecular mass of dextrose = g/mol. Ans: 14.1 atm 20. For the first-order reaction 2N 2 O 5 2N 2 O 4 + O 2 at a particular temperature, the halflife of N 2 O 5 is 0.90 hr. What fraction of the initial concentration of N 2 O 5 will remain after 2.4 hours? Ans:

3 21. For the following exothermic reaction, the rate law at 298 K is rate = k [H 2 ][I 2 ]. H 2 (g) + I 2 (g) 2HI(g) Predict the effect of each of the following changes on the initial rate of the reaction: a. Addition of hydrogen gas at constant temperature and volume b. Increase in volume of the reaction vessel at constant temperature c. Addition of a catalyst d. Increase in temperature Ans: a. The initial rate increases. b. The initial rate decreases. c. The initial rate increases d. The initial rate increases. 22. Aspirin, C 9 H 8 O 4, slowly decomposes at room temperature by reacting with water in the atmosphere to produce acetic acid, HC 2 H 3 O 2, and 2-hydroxybenzoic acid, C 7 H 6 O 3 (this is why old bottles of aspirin often smell like vinegar): C 9 H 8 O 4 + H 2 O HC 2 H 3 O 2 + C 7 H 6 O 3 Concentration and rate data for this reaction are given below. [C 9 H 8 O 4 ] (M) [H 2 O] (M) Rate (M/s) Write the rate law for this reaction and calculate k (be sure to include the correct units). Ans: The rate law is rate = k[c 9 H 8 O 4 ][H 2 O], and the rate constant is When the concentrations of reactant molecules are increased, the rate of reaction increases. The best explanation for this phenomenon is that as the reactant concentration increases, Ans: the frequency of molecular collisions increases 24. According to the collision theory, all collisions do not lead to reaction. Why not all collisions between reactant molecules lead to reaction? Ans: 1. The total energy of two colliding molecules is less than some minimum amount of energy. 2. Molecules that are improperly oriented during collision will not react. 25. An increase in the temperature of the reactants causes an increase in the rate of reaction. The best explanation for this behavior is that as the temperature increases, Ans: the fraction of collisions with total kinetic energy greater than E a increases. 26. At 25 C, the second-order reaction NOCl(g) NO(g) + 1 / 2 Cl 2 (g) is 50% complete after 5.82 hours. How long will it take for the reaction to be 75% complete? Ans: 17.5 hr 3

4 27. Ammonium ion (NH + 4 ) reacts with nitrite ion (NO 2 ) to yield nitrogen gas and liquid water. The following initial rates of reaction have been measured for the given reactant concentrations. Expt. # [NH + 4 ] [NO 2 ] Initial rate (M/hr) Write the rate law (rate equation) for this reaction. Ans: rate = k [NH 4 + ] [NO 2 ] The reaction A + 2B products has the rate law, rate = k[a][b] 3. If the concentration of B is doubled while that of A is unchanged, by what factor will the rate of reaction increase? Ans: Two moles of PCl 5 are placed in a 5.0 L container. Dissociation takes place according to the equation PCl 5 (g) PCl 3 (g) + Cl 2 (g). At equilibrium, 0.40 mol of Cl 2 are present. Calculate the equilibrium constant (K c ) for this reaction under the conditions of this experiment. Ans: Consider the following equilibrium, 4NH 3 (g) + 3O 2 (g) 2N 2 (g) + 6H 2 O(g) kj State whether the concentrations the products would increase, decrease, or remain constant (i) after ammonia was added to the system. (ii) after nitrogen gas was removed from the system (iii) when the temperature is increased. Ans: (i) increase (ii) increase (iii) decrease 31. Consider the equilibrium equation C(s) + H 2 O(g) J CO(g) + H 2 (g). Which way will the reaction shift if (i) the pressure on the system is increased? (ii) the temperature of this system is raised? (iii) If additional gaseous water Ans: (i) (ii) (iii) Towards the reactants Towards the products Towards the products 32. Consider the chemical reaction 2NH 3 (g) N 2 (g) + 3H 2 (g). The equilibrium is to be established in a 1.0 L container at 1,000 K, where K c = Initially, 1,220 moles of NH 3 (g) are present. Calculate K p for the reaction. Ans: 270 4

5 mol of oxygen and 4.0 mol of NO are introduced to an evacuated 0.50 L reaction vessel. At a specific temperature, the equilibrium 2NO(g) + O 2 (g) 2NO 2 (g) is reached when [NO] = 1.6 M. Calculate K c for the reaction at this temperature? Ans: K c = At 700 K, the reaction 2SO 2 (g) + O 2 (g) 2SO 3 (g) has the equilibrium constant K c = , and the following concentrations are present: [SO 2 ] = 0.10 M; [SO 3 ] = 10. M; [O 2 ] = 0.10 M. Is the mixture at equilibrium? If not at equilibrium, in which direction (as the equation is written), left to right or right to left, will the reaction proceed to reach equilibrium? Ans: No, left to right 35. At 700 K, the reaction 2SO 2 (g) + O 2 (g) 2SO 3 (g) has the equilibrium constant K c = , and the following concentrations are present: [SO 2 ] = M; [SO 3 ] = 10. M; [O 2 ] = M. Is the mixture at equilibrium? If not at equilibrium, in which direction (as the equation is written), left to right or right to left, will the reaction proceed to reach equilibrium? Ans: No, right to left mol NOCl was placed in a 2.50 L reaction vessel at 400ºC. After equilibrium was established, it was found that 28% of the NOCl had dissociated according to the equation 2NOCl(g) 2NO(g) + Cl 2 (g). Calculate the equilibrium constant, K c, for the reaction. Ans:

A) sublimation. B) liquefaction. C) evaporation. D) condensation. E) freezing. 11. Below is a phase diagram for a substance.

A) sublimation. B) liquefaction. C) evaporation. D) condensation. E) freezing. 11. Below is a phase diagram for a substance. PX0411-1112 1. Which of the following statements concerning liquids is incorrect? A) The volume of a liquid changes very little with pressure. B) Liquids are relatively incompressible. C) Liquid molecules