Gas properties and behaviours

Characteristics of Gases

• highly compressible

• expand to fill the volume of any container and will exert pressure

• lower densities than solids or liquids.

• change volume dramatically with changing temperature.

• mix with one another readily and thoroughly

pressure

the amount of force applied to an area. p=F/A.

atmospheric pressure

weight of air per unit area.

Units of Pressure

mmHg or torr (same unit)

unit of atmospheric pressure

1 atm= 760 torr

1 standard atmosphere

= 101325 Pa = 1 atm = 760 mm Hg = 760 torr 1 bar = 105 Pa = 100 kPa

Standard Temperature & Pressure

0°C = 273 K

1 atm =101.325 kPa

Variables Affecting Gas Pressure

Increase or decrease the volume of the container. l Increase or decrease the temperature of the gas. l Increase or decrease the number of molecules in the container.bt

Four variables are needed to define the physical condition, or state, of a gas

temperature, pressure, volume, and amount of gas, usually expressed as number of moles.

The Gas laws

The equations that express the relationships among the four variables needed to define the physical condition or a gas. ( temperature, pressure, volume, and ammount of gas)

Boyle’s law

PV=k, The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure.

Charles’ law

V/T=k, the volume of a fixed ammount of gas at a constant pressure is directly proportional to its absolute temperature.

Gay-Lussac’s Law

P/T=k. The pressure and absolute temperature (K) of a gas are directly related at constant mass and volume.

avogadro’s hypothesis

equal volumes of gases at the same temperature and pressure contain equal number of molecules. The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas. V=kn

Ideal-Gas Equation

PV=nRt where,

• P= gas pressure in atm

• V=volume in L

• n= number of moles

• R=universal gas constant (.08206 L atm mol^-1 k^-1)

Dalton’s law of partial pressures

As long as gases in a mixture do not react with one another, the pressure that each gas exerts is specific to the amount of that particular gas, and we will call the pressure of that particular gas its “partial pressure”

Mole fraction

the ratio of moles of a substance in relation to the total moles present.

Dalton’s law of partial pressures equation

P_A=X_A x P_T where,

• P_A= pressure of gas A

• X_A = mole fraction of gas A

• P_T = total pressure