3.2 The Gas Laws

Physical Characteristics of Gases Do gases have variable or definite shape? Do gases have variable or definite volume? Gases assume the volume and shape of their containers. Gases are the most compressible state of matter. Gases will mix evenly and completely when confined to the same container.

Pressure Pressure is the result of a force distributed over an area Pressure= Force/Area Units= 1 Newton/Square meter (N/m²)= 1 pascal (Pa) Example: If you’ve ever inflated a tire, you’ve probably made a pressure measurement in pounds (force) per square inch (area).

What causes gas pressure in a closed container? Think about helium inside a balloon….. Recall that helium atoms in a balloon are constantly moving So what do you think causes the pressure in the balloon? Collisions between particles of gas and the walls of a container cause the pressure in a closed container of gas The more frequent the collisions the greater the pressure

Factors that Affect Gas Pressure Temperature Volume Number of particles Brainstorm for a minute and think how these factors will affect gas pressure

Volume Volume is the three-dimensional space inside the container holding the gas. The SI unit for volume is the cubic meter, m3. A more common and convenient unit is the liter, L. ** think of a 2 Liter soda to get an idea of how big a liter is

Temperature Temperature is the measurement of heat…or how fast the particles are moving. Remember: Not all substance freeze, melt or evaporate at the same temperature.

Number of Particles Think What happens when you add more air to a tire??? Amount of substance: the SI unit for amount of substance is the mole, mol. Since we can’t count molecules, we can convert measured mass (in kg) to the number of moles, n, using the molecular or formula weight of the gas.

Factors that Affect Gas Pressure Temperature Increase temperature increases the pressure if the volume and number of particles are constant Volume Reducing the volume of gas increases the pressure if the temperature of the gas and the number of particles is constant Number of particles Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant

Boyle’s Law P1V1=P2V2 This law is named for Charles Boyle, who studied the relationship between pressure, p, and volume, V, in the mid-1600s. Boyle determined that for the same amount of a gas at constant temperature, results in an inverse relationship: when one goes up, the other comes down. pressure volume Doubling the pressure reduces the volume by half. Conversely, when the volume doubles, the pressure decreases by half.

Charles’s Law V1/T1=V2/T2 This law is named for Jacques Charles, who studied the relationship volume, V, and temperature, T, around the turn of the 19th century. This defines a direct relationship: With the same amount of gas he found that as the volume increases the temperature also increases. If the temperature decreases than the volume also decreases. volume temperature