Atmospheric Pressure:

• Atmospheric pressure is the force exerted by gas molecules in the air as they strike surfaces.

• Measured using a barometer (invented by Torricelli); standard atmospheric pressure is 760 mm Hg.

• Factors such as altitude and weather can affect barometric pressure.

Units of Pressure:

• Common units: atmospheres (atm), millimeters of mercury (mm Hg), torr, pascals (Pa), and pounds per square inch (psi).

• Conversion factors:

  • 1 atm = 760 mm Hg = 760 torr = 101,325 Pa = 14.7 psi

Gas Laws:

• Boyle's Law: At constant temperature, pressure and volume are inversely proportional. P1V1=P2V2

• Charles' Law: At constant pressure, volume and temperature (in Kelvin) are directly proportional. V1T1=V2T2

• Avogadro's Law: At constant temperature and pressure, volume and moles of gas are directly proportional. V1n1=V2n2

• Combined Gas Law: Relates pressure, volume, and temperature for a fixed amount of gas. P1V1T1=P2V2T2

• Ideal Gas Law: Relates pressure, volume, temperature, and moles of gas. PV=nRT where R = 0.0821 L·atm/(mol·K).

Problem-Solving Tips:

• Always use Kelvin for temperature in gas law calculations (K = °C + 273).

• Convert all units to match the gas constant R when using the ideal gas law.

• For combined gas law and other before/after problems, identify which variables are constant and which change.

Applications and Examples:

• Calculating new volumes, pressures, or temperatures when conditions change using the appropriate gas law.

• Using stoichiometry with gas laws to relate moles and volumes at given conditions.

• Understanding that real gases may deviate from ideal behavior under certain conditions (high pressure, low temperature).