1. How Gases Work Objectives: Relate density and temperature to molar mass. Key Terms: Effusion, Lifting Gas, Dalton’s Law, Grahams Law

2. Lifting Gases In fluids, objects that are less dense rise and objects that are more dense sink. This is also true for gases.. Below is a list of the most common gases found in the air around us. – Nitrogen (N 2 ) - 78% mass - 28amu – Oxygen (O 2 ) - 21% mass - 32amu – Trace Gases - 1% (CO 2, Ar, He, H 2, CH 4, H 2 O…) Since the density = mass / vol the density of a gas is directly related to its mass (molar mass for all gases = 22.4L). – The two primary lifting gases are He and H 2 - due to their very low densities Of the two, H 2 has more lifting power but is not used because of the danger of explosion.

3. Lifting Gas Another way of decreasing the density of a gas is to heat it. The ideal gas equation tells us that as we heat a gas is occupies more space (expands). The expansion causes a net drop in density for all of the heated gases in the area. – When the air is heated the balloon ascends - decrease in density (vol increases while mass stays the same) – As the air cools the balloon descends - increase in density

4. Dalton’s Law of Partial Pressures In a sample of gas the total pressure is equal to the sum of the partial pressures. – P 1 + P 2 + P 3 … = P total – (constants: V, T, n)

5. Graham’s Law Diffusion is the property of gases where the particles of gas mix evenly in an enclosed space. – Mixing is from an area of higher to lower concentration. Effusion is the movement of gas through a hole. The rate of effusion and diffusion is inversely related to its mass. Therefore, lighter gases effuse and diffuse faster than heavier gases. – Graham's Law - the rate of effusion is inversely proportional to the square of the gases molar mass – Heat increases the rate of effusion and diffusion. Increases KE Rate A/ Rate B = molar mass B / molar mass A