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How Gases Work

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

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How Gases Work

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  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 (N2) - 78% mass - 28amu • Oxygen (O2) - 21% mass - 32amu • Trace Gases - 1% (CO2, Ar, He, H2, CH4, H2O…) • Since the density = mass/volthe 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 H2 - due to their very low densities • Of the two, H2has 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. • P1 + P2 + P3… = Ptotal • (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

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