Unit 5 Learning Log
1- (a) What conditions are represented by STP (b)What is the molar volume of any gas at STP?
2- You are given two 1 liter flasks and told that one contains a gas of molar mass 30 , the other of molar mass 60, both at the same temperature. The pressure in flask A is X atm and the mass of the gas is 1.2 gm. The pressure in flask B is 0.5X atm and the mass of the gas is 1.2 gm. Which flask has the gas with molar mass = 30
3-Which gas is most dense at 1.00 atm and 298 K. carbon dioxide, dinitrogen oxide or chlorine. Explain?
4- (a) Calculate the density of NO2 gas at 0.970 atm and 35 C(b) calculate the molar mass of a gas if 2.5 gm occupies 0.875 L at 685 torr and 35 C
5 - Hydrogen gas is produced when zinc metal reacts with sulfuric acid. If 159 ml of wet hydrogen is collected over water at 24 C and a pressure of 738 torr, how much zinc was consumed? VP water at 24 C = 22.38 torr
6- Consider a 2.0 L container at 1.00 atm and 25 C containing nitrogen that is connected by a valve to a 3.0 L container at 2.00 atm and 25 C containing oxygen. (a) when the valve is opened , what volume will the nitrogen occupy (b) What is the partial pressure of the nitrogen? (c) what is the partial pressure of the oxygen? (d) what is the total pressure in the system?
7- Vessel A contains CO(g) at 0 C and 1 atm. Vessel B contains SO2(g) at 20 C and 0.5 atm. The vessels are the same volume. (a) which vessel has more molecules (b) which has more mass (c) In which vessel is the average kinetic energy higher (d) In which vessel is the rms speed of the molecules higher.
8- Explain the difference in boiling point between (a) HF(20C) and HCl(-85 C) (b) trichloromethane(61C) and tribromomethane(150C) (c) bromine gas(59 C) and iodine chloride(97 C)
9- The normal melting and boiling points of Xenon are –112 C and –107 C. Its triple point is at –121 C and 282 torr and its critical point is at 16.6 C and 57.6 atm. Sketch the phase diagram and identify the four given points. If Xe gas is cooled at an external pressure of 100 torr will it undergo deposition or condensation. Explain?
10- For each of the following pairs predict the substance with the higher melting point and explain why: (a) B, BF3 (b) Na, NaCl (c) TiO2, TiCl4 (d) LiF, MgF2
11- A 6.19 gram sample of PCl5 is placed in an evacuated 2.00 liter flask and is completely vaporized at 252oC.
(a) Calculate the pressure ion the flask if no chemical reaction were to occur.
(b) Actually at 252oC the PCl5 is partially dissociated according to the following equation:
PCl5 (g) PCl3(g) + Cl2(g)
The observed pressure is found to be 1.00 atmosphere. In view of this observation, calculate the partial pressure of PCl5 and PCl3 in the flask at
252oC
12- Observations about real gases can be explained at the molecular level according to the kinetic molecular theory of gases and ideas about intermolecular forces. Explain how each of the following observations can be interpreted according to these concepts, including how the observation supports the correctness of these theories.
(a) When a gas-filled balloon is cooled, it shrinks in volume; this occurs no matter what gas is originally placed in the balloon.
(b) When the balloon described in (a) is cooled further, the volume does not become zero; rather, the gas becomes a liquid or solid.
(c) When NH3 gas is introduced at one end of a long tube while HCl gas is introduced simultaneously at the other end, a ring of white ammonium chloride is observed to form in the tube after a few minutes. This ring is closer to the HCl end of the tube than the NH3 end.
(d) A flag waves in the wind.
13- Explain each of the following in terms of atomic and molecular structures and/or intermolecular forces.
(a) Solid K conducts an electric current, whereas solid KNO3 does not.
(b) SbCl3 has measurable dipole moment, whereas SbCl5 does not.
(c) The normal boiling point of CCl4 is 77ºC, whereas that of CBr4 is 190ºC.
(d) NaI(s) is very soluble in water, whereas I2(s) has a solubility of only 0.03 gram per 100 grams of water.
14- Account for each of the following observations about pairs of substances. In your answers, use appropriate principles of chemical bonding and/or intermolecular forces. In each part, your answer must include references to both substances.
(a) Even though NH3 and CH4 have similar molecular masses, NH3 has a much higher normal boiling point (-33C) than CH4 (-164C).
(b) At 25C and 1.0 atm, ethane (C2H6) is a gas and hexane (C6H14) is a liquid.
(c) Si melts at a much higher temperature (1,410C) than Cl2 (-101C).
(d) MgO melts at a much higher temperature (2,852C) than NaF (993C).
15- Propane gas flows into a combustion chamber at a rate 250 L/min at 2.0 atmand ambient temperature. Air is added to the chamber at 1.0 atm and the same temperature. The gases are ignited.
a)To get complete combustion of the propane to carbon dioxide and water three times as much oxygen as is stoichiometrically appropriate is required. Assuming air is 21% oxygen and 79% nitrogen, calculate the required flow rate of air?
b )Under the conditions in part a, the combustion is not complete and a
mixture of carbon dioxide and carbon monoxide is produced. It is determined that 94.0% of the carbon in the exhaust gas is present as carbon dioxide. The remainder is carbon monoxide. Calculate the percent composition of the exhaust gas in terms of mole fraction of CO, CO2 , O2 , N2 , and H2O. Assume the propane is completely reacted and the nitrogen is totally unreacted.
16- CONCEPT CLARIFICATION: Explain the following concepts and give a good example of it’s application.
1) Graham's Law
2) major points of kinetic molecular theory
3) Deviations from kinetic molecular theory (properties of molecules +
environmental properties)
4) VanderWaals Equation
17- INTERPARTICLE FORCES: Briefly explain and give an example of each.
1) metallic bond5) dipole-dipole interaction
2) covalent network bond6) London Dispersion force
3) Ionic bond7) Lattice energy
4) Hydrogen Bonding8) covalent bond