Lesson 5.4 – Ideal Gases Chemistry 1 Honors Dr. J. Venables Northwestern High School

Combined Gas Law Hybrid of Boyle, Charles and Gay-Lussac. The one law you need to know; from this you can figure everything. If you know five values, then can calculate sixth. If anything is held constant, you can eliminate it from the equation.

Practice 1. A gas occupies 0.658 L at 137 kPa and 28 ºC. What is the pressure of the gas If the volume is 1.44 L and the temperature is 87 ºC? 2. A gas occupies 3.88 L at 779 mm Hg and 229 K. At what temperature will the gas occupy 2.63 L at 695 mm Hg?

Avogadro’s Principle Avogadro’s Principle: Equal volumes of gases at the same T and P contain equal number of particles. 1000 small He gas atoms occupy the same volume as 1000 larger Xe gas atoms. Particles are so far apart that size has little influence on the volume occupied by fixed number of particles. Not true for solid or liquid

Molar Volume: One mole of gas at STP occupies 22. 4 Liters Molar Volume: One mole of gas at STP occupies 22.4 Liters. STP = standard T & P = 273 K (0°C) and 1 atm (101.325 kPa). What if the gas is not at STP?

Ideal Gas Law Ideal Gas Law: PV = nRT Where P = Pressure V = Volume n = number of moles R = Ideal Gas Constant T = Kelvin Temperature

Ideal Gas Particles take up almost no space Absence of intermolecular forces between gas molecules/atoms. No gas is truly ideal. Under right conditions of T and P, ideal gas law gives good results. Low pressure and high temperature approximates ideal gas behavior. Why?

Practice 1. How many moles of CO2 are in a 1.75 L container at 35°C and 1290 mm Hg? How many grams is that? 2. What is the pressure in a 0.565-L container containing 2.87 g of argon gas at 59.9°C?