Atmospheric Pressure:

• Atmosphere supports life, removes exhaust gases, and shields from radiation.

• All gases exert pressure on their surroundings due to molecular collisions.

• Atmospheric pressure is the force exerted by gases in the atmosphere (mainly N2, O2, Ar, CO2, Ne, He, CH4).

• Measured using a barometer; standard atmospheric pressure is 760 mm Hg.

• Factors affecting barometric pressure include altitude and weather.

Units of Pressure:

• Common units: mm Hg, torr, atm, Pa, psi.

• Conversion: 760 mm Hg=1 atm=101325 Pa=14.7 psi

• Pressures can be converted between units as needed.

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. P1V1T2=P2V2T1

• Ideal Gas Law: Relates pressure, volume, temperature, and moles of gas. PV=nRT

  • P = pressure (atm), V = volume (L), n = moles, R = 0.0821 L·atm/(mol·K), T = temperature (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 gas law problems, identify which variables are constant and which change.

• Use dimensional analysis for unit conversions.

Sample Calculations:

• Use the appropriate gas law based on which variables are held constant.

• For changes in conditions (e.g., temperature, pressure), set up ratios using the relevant law.

• For ideal gas law problems, solve for the unknown (n, V, P, or T) using PV=nRT.

Conceptual Understanding:

• Gas pressure results from molecular collisions with surfaces.

• Volume, pressure, temperature, and amount of gas are interrelated; changing one affects the others according to the gas laws.

• Understanding these relationships is essential for predicting gas behavior under different conditions.