Properties of Gases: Kinetic Molecular Theory and Gas Behavior

1. Chapter 11 Lecture Basic Chemistry Fourth Edition Chapter 11 Gases 11.1 Properties of Gases Learning Goal Describe the kinetic molecular theory of gases and the properties of gases.

2. Chapter Readiness Key Math Skills • Solving Equations (1.4D) Core Chemistry Skills • Using Significant Figures in Calculations (2.4) • Writing Conversion Factors from Equalities (2.6) • Using Conversion Factors (2.7) • Using Molar Mass as a Conversion Factor (7.3) • Converting Moles to Moles (9.1)

3. Gases We are surrounded by gases, such as • elements that exist as a gas at room temperature: H2, N2, O2, F2, Cl2, and noble gases • nonmetal oxides including: CO, CO2, NO, NO2, SO2, and SO3 • low-molecular-weight hydrocarbons, methane, ethane, propane, and butane

4. Gas Behavior The behavior of gases is quite different from that of liquids and solids. • Gas particles are much farther apart than particles in a liquid or solid. • Gases have no definite shape or volume, but will completely fill any container. • Gases are less dense than solids or liquids and easy to compress.

5. Gases, Kinetic Molecular Theory The Kinetic Molecular Theory of gases states: 1. A gas consists of small particles (atoms or molecules) that move randomly with high velocities. 2. The attractive forces between particles of a gas are usually very small.

6. Gases, Kinetic Molecular Theory The Kinetic Molecular Theory of gases states: 3. The actual volume occupied by gas molecules is very small compared to the volume the gas occupies. 4. Gas particles are in constant motion, moving rapidly in straight paths.

7. Gases, Kinetic Molecular Theory The Kinetic Molecular Theory of gases states: 5. The average kinetic energy of gas molecules is proportional to the Kelvin temperature.

8. Pressure (P) When gas particles strike the walls of the container, they exert pressure. If we heat the gas, the molecules move faster and strike the walls of the container more often with increased force, increasing the pressure. Figure 11.1 Gas particles move in straight lines within a container. The gas particles exert pressure when they collide with the walls of the container.

9. Atmospheric Pressure Atmospheric pressure • is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth • is about 1 atmosphere or a little less at sea level

10. Volume (V) The volume of a gas equals the size of the container in which the gas is placed. In a container with a flexible volume: • adding more particles increases the volume • lowering the temperature of the gas reduces the kinetic energy of the molecules, decreasing the volume of space they occupy

11. Temperature (T) The temperature of a gas is related to the kinetic energy of its particles and is measured in Kelvin. For example, in a rigid container, heating the gas will increase the energy of the molecules and therefore increase the pressure of the gas inside the container.

12. Amount of Gas (n) Adding air to a bicycle tire increases the amount of gas in the tire, resulting in a higher pressure inside the tire. Usually, the mass of a gas is measured in grams. In gas law calculations, we change the grams to moles.

13. Properties that Describe a Gas

14. Learning Check Identify the property of a gas that is described by each of the following: • increases the kinetic energy of gas particles • the force of gas particles hitting the walls of the container • the space occupied by a gas

15. Solution Identify the property of a gas that is described by each of the following: • increases the kinetic energy of gas particles Temperature • the force of gas particles hitting the walls of the container Pressure • the space occupied by a gas Volume