Introductory Chemistry, 3rd Edition Nivaldo Tro Chapter 11 Gases

11.2-11.3 Tro's Introductory Chemistry, Chapter 11

Properties of Gases Expand to completely fill their container. Take the shape of their container. Low density. Much less than solid or liquid state. Compressible. Mixtures of gases are always homogeneous. Fluid. Tro's Introductory Chemistry, Chapter 11

The Structure of a Gas Gases are composed of particles that are flying around very fast in their container(s) They move in straight lines until they encounter something Particles in a gas, you would find that there is a lot of empty space Tro's Introductory Chemistry, Chapter 11

Kinetic Molecular Theory Particles (either atoms or molecules) are constantly moving The attraction between particles is negligible When the moving particles hit another particle or the container, they do not stick, but they bounce off and continue moving in another direction. Like billiard balls. Tro's Introductory Chemistry, Chapter 11

Kinetic Molecular Theory of Gases There is a lot of empty space between the particles in a gas. Compared to the size of the particles. The average kinetic energy of the particles is directly proportional to the Kelvin temperature. As you raise the temperature of the gas, the average speed of the particles increases. But don’t be fooled into thinking all the particles are moving at the same speed!! Tro's Introductory Chemistry, Chapter 11

Kinetic Molecular Theory Tro's Introductory Chemistry, Chapter 11

Gas Particles Pushing Gas molecules are constantly in motion As they move and strike a surface, they push on that surface. Push = force. If we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting. Pressure = force per unit area. Tro's Introductory Chemistry, Chapter 11

The Effect of Gas Pressure The pressure exerted by a gas can cause some amazing and startling effects. Whenever there is a pressure difference, a gas will flow from area of high pressure to low pressure. The bigger the difference in pressure, the stronger the flow of the gas. If there is something in the gas’ path, the gas will try to push it along as the gas flows. Tro's Introductory Chemistry, Chapter 11

Gas Properties Explained Gases have taken the shape and volume of their container(s) In solids and liquids, the particles are attracted to each other strongly enough so they stick together. Gases are compressible and have low density because of the large amount of unoccupied space between the particles. Tro's Introductory Chemistry, Chapter 11

Properties—Indefinite Shape and Indefinite Volume Because the gas molecules have enough kinetic energy to overcome attractions, they keep moving around and spreading out until they fill the container. As a result, gases take the shape and the volume of the container they are in. Tro's Introductory Chemistry, Chapter 11

Properties—Compressibility Because there is a lot of unoccupied space in the structure of a gas, the gas molecules can be squeezed closer together. Tro's Introductory Chemistry, Chapter 11

Gas Properties Explained— Low Density Because there is a lot of unoccupied space in the structure of a gas, gases do not have a lot of mass in a given volume, the result is that they have low density. Tro's Introductory Chemistry, Chapter 11

The Pressure of a Gas Pressure is the result of the constant movement of the gas molecules and their collisions with the surfaces around them. The pressure of a gas depends on several factors: Number of gas particles in a given volume. Volume of the container. Average speed of the gas particles. Tro's Introductory Chemistry, Chapter 11

Density and Pressure Pressure is the result of the constant movement of the gas molecules and their collisions with the surfaces around them. When more molecules are added, more molecules hit the container at any one instant, resulting in higher pressure. Also higher density. Tro's Introductory Chemistry, Chapter 11

Air Pressure The atmosphere exerts a pressure on everything it contacts. On average 14.7 psi. The atmosphere goes up about 370 miles, but 80% is in the first 10 miles from Earth’s surface. This is the same pressure that a column of water would exert if it were about 10.3 m high. Tro's Introductory Chemistry, Chapter 11

Measuring Air Pressure Use a barometer. Column of mercury supported by air pressure. Force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury. gravity Tro's Introductory Chemistry, Chapter 11

Atmospheric Pressure and Altitude The higher up in the atmosphere you go, the lower the atmospheric pressure is around you. At the surface, the atmospheric pressure is 14.7 psi, but at 10,000 ft is is only 10.0 psi. Tro's Introductory Chemistry, Chapter 11

Common Units of Pressure Average air pressure at sea level Pascal (Pa) 101,325 Kilopascal (kPa) 101.325 Atmosphere (atm) 1 (exactly) Millimeters of mercury (mmHg) 760 (exactly) Inches of mercury (inHg) 29.92 Torr (torr) Pounds per square inch (psi, lbs./in2) 14.7 Tro's Introductory Chemistry, Chapter 11

Convert 45.5 psi into kPa. Tro's Introductory Chemistry, Chapter 11