Question

CHE 151-3rd Write your answers in the Blue Book provided. Start each new question at the top of a new page. To receive full credit for problems, you must show the correct setup with units and give your answer with the correct number of significant figures. 1.a) A barometer reads 1.43 atm. Calculate the pressure in mm Hg, and torr. b) If 4.50 L of oxygen is cooled at constant pressure from 200 oC to 25 oC, what is the new volume of oxygen? 2. a) A balloon filled with helium contains 3.5L at 1.925 atm and 23oC. What is the new pressure of the helium in the volume is decreased to 0.50 L and -50oC? 3. Calculate the volume occupied by 88.2 g of CO2 at 0.955 atm and 25°C. R = 0.08206 Lxatm/Kxmol. 4. Two identical flasks of the same volume are labeled A and B. Flask A contains NH3(g) at 50¬-oC and flask B contains HCl (g)¬ at 50oC. KE=1/2 mv2. a) Which molecule is moving the most rapidly? Explain. b) Give two ways you could increase the pressure in the flask containing the NH3(g) c) Do both molecules have the same kinetic energy? Justify your answer. 5. The following reaction is used to generate hydrogen gas in the laboratory. If 243 mL of gas is collected at 25.0°C and has a total pressure of 745.5 mm Hg, what mass of hydrogen (in grams) is produced? Make sure your units work. (vapor pressure of water at 25oC = 23.8 mm Hg) 6.a) In terms of wavelength, frequency and energy compare the two photons with wavelengths of 900 nm and 780 nm. b) What are the emission spectra of an element? c) How are the emission spectra of an element produced? d) How did Bohr (quantum theory) explain the emission (line) spectra of hydrogen? 7.a) A laser used to dazzle the audience in a rock concert emits green light with a wavelength(λ) of 515 nm. Calculate the frequency of the light. (v=c/λ; c=3.00x108m/s; 1nm=10-9m) Show set-up and give answers with the correct number of significant figures. b) Green light has a frequency of about 6.00x1014 s-1. What is the energy of green light? (h=6.626x10¬-34 J∙s). 8. a) What is the purpose of the Quantum Mechanic theory of the atom? b) State the two assumptions of the quantum mechanic theory. c) The four quantum numbers can be considered as labels for any electron in the atom represented by n, l, ml, ms . What property of the electron on the energy level do each of these values describe? 9. a) What are the four quantum numbers of the only electron in Hydrogen? b) When n= 3, what are all the values for l, ml, ms? c) Give the n,l, ml, ms for all the electrons in an atom of Be, atomic number 4 (4 electrons). 10. Phosphorus reacts with iodine as shown in the chemical reaction: 2P(s) + 3I2(s)  2PI3(s) If 28.2 g PI3 is obtained from the reaction of 48.0 g of I2 with 50,0 grams of phosphorus, a) Calculate the theoretical yield for the reaction. b) What Substance is the limiting reagent for this reaction? Explain.

Answer 1

1)

a)

Pressure = 1.43 atm

1 atm = 760 mm Hg = 760 torr

1.43 atm = 760 mm Hg/1 atm * 1.43 atm

          = 1086.8 mm Hg = 1086.8 torr

b)

At constant pressure V1/T1 = V2/T2

V1 = initial volume and V2 = Final volume

T1 = initial temperature and T2 = Final temperature

4.5/200 = V2/25

V2 = Final volume = 0.5625 L

2)

a)

According to Ideal gas equation PV = nRT

P1V1/T1 = P2V2/T2

P1 = initial pressure and P2 = Final Pressure

V1 = initial Volume and V2 = Final Volume

T1 = Initial Temperature and T2 = Final Temperature

1.925 * 3.5/(23+273.15) = P2 * 0.5/(-50+273.15)

P2 = 10.1534 atm = Final Pressure of the gas

3)

According to Ideal Gas equation PV = nRT

0.955 * V = 88.2/44.1 * 0.08206 * (25 + 273)

V = volume of CO2 gas = 51.2123 L