Gas Laws

Properties of Gases Expand to completely fill their container Take the shape of their container Low density – mass divided by volume. Take up much more space than their mass. Much less than solid or liquid state Compressible Mixtures of gases are always homogeneous

Characteristics of Gases Gases can be compressed. low volume = lots of empty space Gases undergo diffusion & effusion

Factors That Affect Gases Pressure – the force that a gas exerts on a given area of a container. Volume – the space inside a container holding the gas. Concentrations (Moles) – amount of the gas. We can convert to mass using molecular weight. Temperature – the average speed of the gas particles.

Pressure Conversions KEY UNITS AT SEA LEVEL 101.3 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi *These are all equal to each other!

Pressure Conversions A) 2.5 atm = ? kPa 2.5 atm 101.3 kPa 1 atm B) 200 torr = ? mmHg 200 torr 760 mmHg 760 torr = 200 mmHg C) 35 psi = ? atm D) 1200 torr = ? atm 35 psi 1 atm 14.7 psi = 2.4 atm 1200 torr 1 atm 760 torr = 1.6 atm

Temperature Conversions Always use absolute temperature (Kelvin) when working with gases. ºF ºC K -459 32 212 -273 100 273 373 K = ºC + 273

Temperature Conversions A) 10 ºC = ? K B) 300 K = ? ºC 10 ºC + 273 = 283 K 300 K – 273 = 27 oC

Standard Temperature & Pressure STP STP Standard Temperature & Pressure 273 K 1 atm

Boyles’ Law If the temperature remains constant, the volume and pressure vary inversely i.e. if Pressure ↑, then Volume ↓; and vice versa P1 V1 = P2 V2

Boyle’s Law (cont.)

Boyles’ Law Example If a gas has a volume of 200 ml at 800 mmHg pressure, calculate the volume of the same gas at 765 mmHg. P1= 800mmHg V1= 200ml P2 =765mmHg V2=? Formula P1 V1 = P2 V2

Formula P1V1 = P2V2 Plug in values 800 mmHg x 200 ml = 765 mmHg x V2 Solve V2= 800mmHg x 200ml 765mmHg V2 = 209.15ml

Charles’ Law If the pressure remains constant, the volume and temperature vary directly i.e. if Temperature ↑, then Volume ↑; and vice versa V1 V2 T1 T2 =

Charles’ Law (cont.)

Charles’ Law Example The volume of a gas at 20°C is 500ml. Find its volume at standard temperature if the pressure is held constant. T1= 20°C +273 V1= 500ml T2 = 0°C +273 V2=?

Formula V1 = V2 T1 T2 Plug in values 500ml V2 293K 273K Solve V2= 273K x 500ml 293K V2 = 465.87ml =

Gay Lussac’s Law If the volume remains constant, the temperature and pressure vary directly i.e. if Pressure ↑, then Temperature ↑. *And vice versa P1 P2 T1 T2 =

Pressure and Temperature (cont.)

Gay-Lussac’s Example A steel tank contains a gas at 27°C and a pressure of 12 atm. Determine the gas pressure when the tank is heated to 100°C. T1= 27°C +273 P1= 12 atm T2 = 100°C +273 P2=?

P1 = P2 T1 T2 Plug in values 12 atm P2 300K 373K Solve P2 = 373K x 12atm 300K P2 = 14.92 atm =