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The Nature of Gases

The Nature of Gases. Objectives: 1. Describe the nature of gases and recognize that gases have mass, can be compressed, exert pressure, occupy the space available to them, and diffuse.

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The Nature of Gases

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  1. The Nature of Gases Objectives: • 1. Describe the nature of gases and recognize that gases have mass, can be compressed, exert pressure, occupy the space available to them, and diffuse. • 2. State the six postulates of the Kinetic-molecular theory and explain how they account for the physical properties of gases. Key Terms: • Diffusion, elastic, Kinetic-molecular theory

  2. Nature of Gases Molecules exist as monatomic, diatomic and polyatomic molecules. Below are some basic properties of gas molecules. • Gases have mass • Gases are compressible • Gases will fill the space available to them • Gases diffuse through each other very rapidly • Gases exert pressure • The pressure of a gas depends on its temperature

  3. Kinetic Molecular Theory • The Kinetic-molecular Theory attempts to explain the behavior of gas molecules based on the nature of gas. The theory is grounded on three basic assumptions: • All gases have mass but are very far apart • Gas molecules are separated from each other by extremely large distances • gases can be compressed • gases have low density • Gases particles are constantly moving at a very rapid rate • explains why gases immediately fill a container • gases move in a strait line until colliding with an object • gases freely diffuse through each other • Collisions between gas molecules are perfectly elastic • there is no loss or gain in kinetic energy • kinetic energy (1/2 mv2) of the gas molecules increases with added temperature • explains the expansion of gases when heated • it is important to remember that the temperature of a substance is the average KE of the molecules

  4. Gas Pressure – closed container • force exerted by the collisions of the gas molecules over the surface of an object • force/unit area

  5. Gas Pressure – atmosphere • Atmospheric (air) pressure is the result of the mass of the molecules of gas and the gravity of the Earth. • Pressure of gas at sea level is 760 mmHg - 1atm - 101.3kPa • The millibar is used by the National Weather Service - (1013 millibars = 1 atm at sea level) • Air pressure decreases with altitude • Can be measured using a mercury barometer

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