Gas Laws and Properties

Gases

• Objectives include calculating gas pressure/volume, determining pressure of gas mixtures/components, determining product/reactant amounts in gas phase reactions, and discussing gas properties/behavior.
• Gases are abundant in surroundings, such as the environment, home, and other places.
• Gases are in the air, which supplies us with breathable gases.
• Gases (liquid petroleum gas) are used for heating/cooking in the kitchen.
• Gases aid breathing in hospitals.
• Gases are burned in cars.
• Carbon dioxide makes carbonated drinks refreshing.

Kinetic Molecular Theory

• Molecules of gases are relatively apart and do not attract each other.
• Molecules of gases are in constant rapid, chaotic motion, colliding with container walls and generating gas pressure.
• Perfect elasticity is a characteristic of all molecular collisions, resulting in no decrease in total kinetic energy.
• The average kinetic energy of gas molecules is proportional to the absolute temperature; the average kinetic energies of all gas molecules are the same at the identical absolute temperature.

Pressure

• Pressure is defined as the amount of force exerted per unit, P=F/A, where P is Pressure, F is Force, and A is Area.
• Various units for pressure measurement include:
• Pounds per square inch (psi)
• Kilopascal (KPa)
• Newton per square meter, N/m2
• Atmosphere (atm)
• Torr (or mmHg)

Other Parameters

• Volume can be measured in L or mL.
• Temperature can be measured in Celsius, Fahrenheit, or Kelvin.

Gas Laws

• Boyle's Law
• Charles' Law
• Avogadro's Law

Boyle's Law

• The volume of a given amount of gas is inversely proportional to its pressure at a constant temperature.
• The formula P1V1 = P2V2 is valid with a constant temperature and amount of gas.
• As volume increases, the pressure of a gas decreases proportionally, and vice versa when temperature is constant.

Charles Law

• With constant pressure, the volume of a given amount of gas is directly proportional to its absolute temperature.
• Formula used is V1/T1 = V2/T2.
• The amount of gas and the pressure are constant with this formula.
• Temperature should be expressed in Kelvin (K).
• Temperature increases as a gas expands, conversely, temperature will decrease as a gas decreases in volume.

Avogadro's Law

• At constant temperature and pressure, two gases with the same volume contain the same number of molecules.
• The formula for Avogadro’s Law is V1/n1 = V2/n2

Gay-Lussac's Law

• A gas's pressure is directly proportional to temperature, assuming volume and the number of moles are constant.
• The formula for Gay-Lussac's Law is P1/T1 = P2/T2

Combined Gas Law

• Combined Gas Law PV1/T1 = PV2/T2 can be rearranged into an equation that holds true for a given amount.
• Combined gas laws reduces to Boyle's Law when temperature is constant (T1=T2) PV1 = PV2.
• Combined gas law reduces to Charles's law when pressure is kept constant (P1 = P2): V1/T1 = V2/T2.
• Pressure of a gas is directly proportional to its absolute temperature, when volume is kept constant.: P1/T1 = P2/T2.

Ideal Gas Equation

• The ideal gas law states that for a specific amount of gas, the product of pressure and volume is directly proportional to the absolute temperature.
• All gases contain the same number of gas molecules when under equal temperature, volume, and pressure.
• PV = nRT, where:
• P = Pressure
• V = Volume
• n is the number of moles
• R is the gas constant (0.0821)
• T = Temperature in Kelvin

Dalton's Law of Partial Pressure

• Dalton's law of partial pressures states that the total pressure exerted by a mixture of gases equals the sum of the partial pressures exerted by each individual gas in the mixture.
• PT = P1 + P2 + P3 + ...