Ceneral Chemistry Second Exam 2020

General Chemistry Second Exam Chemistry Department Time: 60 min. Name:____________________________________ Registration Number:_________________________ Instructor:_______________________________ Seat No: _______ Day/Time:__________________ Answer Sheet K = °C+273, 1atm = 760mmHg, R = 0.082057L.atm/(K.mol) = 8.314J/(K.mol), 1.atm = 101.3J, N_A = 6.022x10^23, h = 6.63x10^-34 J.s, R_H = 2.18x10^-18 J, c = 3x10^8 m/s, PV = nRT, u_rms = √(3RT/M), KE = (3/2)RT = N_A(1/2 mu^2) , ΔE = ΔH - PΔV ΔE = q + w, c = λv, E= hv, E_n = -R_H (1/n^2), λ = h/(mu) a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e a b c d e n = m / MM n = 0.018 P= nRT/V n= PV/RT = (1 x 0.401) / (0.082057 x 273.15) 1] Determine the molar mass of a gas if 0.401 L weighs 1.55g at STP? a) 69.3 g/mol b) 94.5 g/mol c) 86.6 g/mol d) 53.3 g/mol e) 43.3 g/mol Pt = PH2 + PH2O --> PH2 = 988 - 118 = 870 mm Hg 2] In a reaction of calcium metal with water, the volume of hydrogen gas collected at 50°C and pressure of 988 mm Hg is 441 mL. What is the mass (in grams) of the hydrogen gas obtained? The vapor pressure of water at 50°C is 118 mmHg. (Molar mass of H2 = 2.016 g/mol ) a) 0.0436g b) 0.0384g c) 0.0190g d) 0.0242g e) 0.0488g n = PV/RT = 3] Calculate the mass of calcium (in g) that must be dissolved in sulfuric acid in order to obtain 500ml of hydrogen gas at 20°C and 770 mmHg? (Molar mass of Ca = 40.08 g/mol ) Ca(s) + H2SO4 (aq) -> CaSO4(s) + H2(g) a) 1.38 g b) 0.0425 g c) 1.24 g d) 0.84 g e) 1.18 g n = PV/RT = (770 x 0.500) / 0.082057 x (20+273) 4] What is the kinetic energy of a mole of CO2 at 200K (in kJ)? a) 200 kJ b) 4.14x10^-24 kJ c) 2.5x10^-23 kJ d) 0.200 kJ e) 2.49 kJ (Handwritten calculations): √ 3RT/MM √ = 3 x 8.314 x 200/44 = 12.016 / (2 x 16) x 10^-3 KE = 1/2mv^2 = 3/2 RT = 3/2 R T = (3/2 * 8.314 * 200)/ 1000 K L-atm K mole 5] Which of the following is a wrong statement? a) H2 gas behaves more ideally than CO2 gas. b) CO2 (44 g/mol ) effuses faster than N2(g) (28 g/mol ) at STP c) At the same temperature molecules of a gas with low molar mass have higher average velocity than heavier molecules d) Average kinetic energy depends only on temperature e) Real gases behaves as ideal gases at low pressure and high temperature u_rms = √(3RT/MM) 6] Calculate the root mean square velocity (u_rms) in (m/s) of CO2 molecules in a sample of CO2 gas at 1.0 °C [molar mass of CO2 = 44.0 g/mol ] a) 394 b) 44.0 c) 1.24 d) 39.2 e) 12.5 7] A gas is allowed to expand, at constant temperature, from a volume of 3.0 L to 8.0 L against external pressure of 1.10 atm. If the gas absorbs 350 J of heat from the surroundings, then ΔE in J: a) -345 b) +207 c) -907 d) +345 e) -207 ΔE = ΔH - PΔV ΔE = q + w w = -PΔV q = +350J w = -1.10 x (8-3) ΔV>0 w= -5.5 8] Consider the combustion of isooctane C8H18 (Molar mass = 114 g/mol ): 2 C8H18(l) + 25 O2 --> 16CO2 + 18H2O(l) ΔH = -10930 kJ Calculate the energy released when 105 g of isooctane are combusted in excess oxygen? a) 2.19x10^4 kJ b) 1.01x10^4 kJ c) 5.03x10^3 kJ d) 2.52x10^3 kJ e) 2.01x10^4 kJ (handwritten calculations): 105/114 = 0.92 2 -> -10930 ΔH = nΔH / 2 mol = -10930 kJ ΔE = q +w ΔE = ΔH - PΔV ΔH = H_f 9] When 500.0 mL of 0.400 M Ca(NO3)2 is added to 500.0 mL of 0.800 M NaF, CaF2 precipitates, as shown in the net ionic equation below. The initial temperature of both solutions is 20.00 °C. Assuming that the resulting solution has a mass of 1000.00 g and a specific heat of 4.18 J/(g.°C) calculate the final temperature of the solution. Ca^2+(aq) + 2F^-(aq) --> CaF2(s) ΔH° = -11.5 kJ a) 18.90 °C b) 20.00 °C c) 19.45 °C d) 20.55 °C e) 21.10 °C Ca(NO3) + NaF 500 ml 500 ml 0.400 M 0.8 M 20°C (handwritten calculations) m = 1000g s = 4.18 q = msΔT 2.395x10^-3 = ΔT 11.5 = 1000 x 4.18 x (T_f - 20) TF =