Gases. Chapter 12 pp. 470-508. General properties & kinetic theory. Gases are made up of particles that have (relatively) large amounts of energy. A gas has no definite shape or volume and will spread out to fill as much space as possible.
Chapter 12 pp. 470-508
1 atm = 760 mmHg = 760 torr = 101325 Pa = 101325 N/m2
Use the factor labeling method to perform the following conversions
1. 1,657 mmHg to N/m2
2. 832 torr to atmospheres
3. 17.8 kPa to atmospheres
4. 120,000 Pa to mmHg
1. Gases are composed of tiny atoms or molecules (particles) whose size is negligible compared to the average distance between them. This means that the volume of the individual particles in a gas can be assumed to be negligible (close to zero).
2. The particles move randomly in straight lines in all directions and at various speeds.
3. The forces of attraction or repulsion between two particles in a gas are very weak or negligible (close to zero), except when they collide.
4. When particles collide with one another, the collisions are elastic (no kinetic energy is lost). The collisions with the walls of the container create the gas pressure.
5. The average kinetic energy of a molecule is proportional to the Kelvin temperature and all calculations should be carried out with temperatures converted to K.
2. The pressure on a 415 mL sample of gas is decreased form 823 mmHg to 791 mmHg. What will the new volume of the gas be?
1. A 12.0L sample of air is collected at 296K and then cooled by 15K. The pressure is held constant at 1.2 atm. Calculate the new volume of the air.
2. A gas has a volume of 0.672L at 35oC and 1 atm pressure. What is the temperature of a room where this gas has a volume of 0.535L at 1 atm?
1. Assuming that the gas behaves ideally, how many moles of hydrogen gas are in a sample of H2 that has a volume of 8.16L at a temperature of 0ºC and a pressure of 1.2 atm?
2. A sample of aluminum chloride weighing 0.1g was vaporized at 350ºC and 1 atm pressure to produce 19.2cm3 of vapor. Calculate a value for the MW of aluminum chloride.
(P + a(n/V)2)·(V-nb) = nRT
a and b are constants, where a corrects for intermolecular forces and b corrects for molecular volume
PVm = nRT
2NH4Cl(s) + Ca(OH)2(s) 2NH3(g) + CaCl2(s) + 2H2O(g)
Root Mean Square of the energy of the particles
A typical plot showing the variation in particle speeds is shown below for hydrogen gas at 273K..
μrms = (3RT / MW)1/2
Where R = universal gas constant = 8.3145 kg·m2/s2 mol·K, T = temperature in Kelvin, MW = molar mass of the gas in kg/mol.