Chapter 2 – The Behaviour of Gases – Sections 2.4 to 2.6 CHM1111 Section 04 Instructor: Dr. Jules Carlson Class Time: M/W/F 1:30-2:20

Housekeeping You are not responsible for sections 2.7 and 2.8 of your text. I have set up lecture notes online at http://chem1111notes.weebly.com

Gas Stoichiometry Problem #1 Hydrogen sulfide reacts with sulfur dioxide to give H2O and S. Assume no change in T or P. H2S(g) + SO2(g)  H2O(g) + S(s) If a 20 L container at 15 C has equal concentrations of H2S and SO2 with a total pressure of 450 kPa, what mass of solid sulfur is produced? What is the mole fraction for H2O in the final mixture, providing the reaction goes to completion?

Gas Stoichiometry Problem #2 Carbon monoxide and molecular oxygen react to form carbon dioxide. A 50.0 L reactor at 25.0 ⁰C is charged with 1.00 bar of CO. The gas is then pressurized with O2 to give a total pressure of 3.56 bar. The reactor is sealed, heated to 350 ⁰C to drive the reaction to completion, and cooled back to 25.0 ⁰C. Compute the final partial pressure of each gas.

Gas Density At fixed T, ρ increases linearly with p   At fixed T, ρ increases linearly with p At fixed p, ρ decreases linearly with T For different gases with same T, p, ρ increases linearly with molar mass.

Gas Properties Problem Hydrocarbons are good fuels because they burn in air to generate heat. A sample of hydrocarbon with mass = 1.63 g exerts a pressure of 1.50 bar in a 945 mL bulb at 21.5 ⁰C. What is the molar mass of the hydrocarbon? What is the density of the hydrocarbon if the pressure is reduced to 1.00 bar with constant temperature and hydrocarbon mass?

Molecular View of Gases Speeds of molecules can be measured using a molecular beam apparatus. The speeds of molecules when plotted give a distribution like the one above. So what causes this variation in speed?

Speed and Energy  

Kinetic Molecular Theory The Kinetic Theory describes gases as a large number of small particles that are in constant random motion. Movement not caused by static repulsions, but from collisions. Movement is faster at higher temperatures. At higher temperatures, molecules have more kinetic energy.

Speeds of Gases vs. Mass Heavier molecules move faster, and a distribution in speeds of same compound. Speed of gas movement dependent upon kinetic energy. Smaller gases have higher velocities for same kinetic energy. Speeds of H2, CH4, and CO2 molecules at 300 K.