The Behavior of Gases The word kinetic refers to motion The energy an object has because of its motion is called kinetic energy. According to the kinetic theory, all matter consists of tiny particles that are in constant motion. The particles in a gas are usually molecules or atoms. The temperature of a substance is the measure of its kinetic energy

The Behavior of Gases The kinetic theory as it applies to ideal gases includes: 1. The particles in a gas are considered to be small, hard spheres with an insignificant volume. Within a gas, the particles are relatively far apart compared with the distance between particles in a liquid or solid. Between the particles, there is empty space. No attractive or repulsive forces exist between the particles.

The Behavior of Gases 2. The motion of particles in a gas is rapid, constant, and random. Gases fill their containers regardless of the shape and volume of the containers and can spread out into space without limit. The particles travel in straight-line paths until they collide with another particle and then change direction only when they rebound from collisions. 3. All collisions between particles in a gas are perfectly elastic. During an elastic collision, kinetic energy is transferred without loss from one particle to another. The total kinetic energy remains constant.

The Behavior of Gases Ideal gases differ from real gases The following are not true of real gases Its particles could have no volume. There are no attraction between particles in the gas. Its collisions are elastic There is no gas for which these assumptions are true. An ideal gas does not exist A real gas can behave like an ideal gas, at certain conditions They differ most at low temperatures and high pressures

The Behavior of Gases Gas pressure results from the force exerted by a gas per unit surface area of an object. Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object If no particles are present, no collisions can occur. Consequently, there is no pressure. An empty space with no particles and no pressure is called a vacuum.

The Behavior of Gases This model shows identical air samples in two different containers. Each container has 8 nitrogen molecules and 2 oxygen molecules. In the smaller container, the air sample is compressed, and the molecules are closer together. In the larger container, the molecules are farther apart.

The Behavior of Gases Air exerts pressure on Earth because gravity holds the particles in air within Earth’s atmosphere. The collisions of atoms and molecules in air with objects results in atmospheric pressure. A barometer is a device that is used to measure atmospheric pressure.

The Behavior of Gases The SI unit of pressure is the pascal (Pa). Normal atmospheric pressure is about 100,000 Pa, that is, 100 kilopascals (kPa). Two older units of pressure are commonly used. millimeters of mercury (mm Hg) atmospheres (atm) Equivalents of different pressures are: 1 atm 101.3 kPa 760 mm Hg

The Behavior of Gases Standard pressure is defined as 1 atm Standard temperature is 0 °C 0 Kelvin is defined as absolute zero Temperature is the measure of the kinetic energy of the particles When all particle motion ceases, the energy is zero (absolute zero) To convert from Celsius to Kelvin, use the following relationship: K = 273 + ° C

The Behavior of Gases The gas laws are mathematical expressions that describe the relationship between the volume, pressure, temperature, and number of particles of a gas Boyle’s Law states that the volume of a fixed mass of gas varies inversely with pressure at constant temperature P1  V1 = P2  V2

The Behavior of Gases A balloon contains 30.0 L of helium gas at 103 kPa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0 kPa? (Assume that the temperature remains constant.)

The Behavior of Gases Charles’s Law states that the volume of a fixed mass of gas at a constant pressure varies directly with the Kelvin temperature V1 V2 T1 T2 = A balloon inflated in a room at 24 °C has a volume of 4.00 L. The balloon is then heated to a temperature of 58 °C. What is the new volume if the pressure remains constant?

The Behavior of Gases Gay-Lussac’s Law states that the pressure of a fixed mass of gas at a constant volume varies directly with the Kelvin temperature P1 P2 T1 T2 =

The Behavior of Gases Aerosol cans carry labels warning not to incinerate (burn) the cans or store them above a certain temperature. The gas in a used aerosol can is at a pressure of 103 kPa at 25 °C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 °C?

The Behavior of Gases The three gas laws can be combined to create the Combined Gas Law States the relationship between pressure, volume, and temperature of a fixed amount of gas V1P1 V2P2 T1 T2 =

The Behavior of Gases The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa pressure. What would the volume be at standard temperature and pressure (STP)?

The Behavior of Gases Each of the gas laws describes how pressure, temperature, and volume can change None of those laws include how the number of particles can change The volume occupied by a gas at a specified temperature and pressure depends on the number of particles. The number of moles of gas is directly proportional to the number of particles.

The Behavior of Gases The gas law that includes all four variables—P, V, T, n—is called the ideal gas law. PV = nRT P = pressure V =volume n = mole (directly proportional to particles) R = a constant T = temperature

The Behavior of Gases PV = nRT We can solve for R, the ideal gas law constant, because we know that 1 mole of gas occupies 22.4 L at STP (101.3 kPa and 273 K) (101.3 kPa)(22.4 L) = R (1 mol)(273 K) R = 8.31 L·kPa/ mol·K

The Behavior of Gases At 34oC, the pressure inside a nitrogen-filled tennis ball with a volume of 0.148 L is 212 kPa. How many moles of nitrogen gas are in the tennis ball?

The Behavior of Gases A deep underground cavern contains 2.24 x 106 L of methane gas (CH4) at a pressure of 1.50 atm and a temperature of 315 K. How many grams of CH4 does the cavern contain?