Gas Laws

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

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

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

Pressure Conversions b KEY UNITS AT SEA LEVEL 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 B) 200 torr = ? mmHg C) 30 psi = ?atmD) 1200 torr = ? atm

Temperature Conversions ºF ºC K K = ºC b Always use absolute temperature (Kelvin) when working with gases.

Temperature Conversions A) 10 ºC = ? K B) 300 K = ? ºC

STPSTP Standard Temperature & Pressure 273 K 1 atm STP

Boyles’ Law b If the temperature remains constant, the volume and pressure vary inversely b i.e. if Pressure ↑, then Volume ↓; and vice versa P 1 V 1 = P 2 V 2

Boyle’s Law (cont.)

Boyles’ Law Example b If a gas has a volume of 200 ml at 800 mmHg pressure, calculate the volume of the same gas at 765 mmHg. b P 1 = 800mmHg b V 1 = 200ml b P 2 =765mmHg b V 2 =? Formula P 1 V 1 = P 2 V 2

b Plug in values b 800 mmHg x 200 ml = 765 mmHg x V 2 b SolveV 2 = 800mmHg x 200ml b 765mmHg b V 2 = ml

Charles’ Law b If the pressure remains constant, the volume and temperature vary directly b i.e. if Temperature ↑, then Volume ↑; and vice versa V 1 V 2 T 1 T 2 =

Charles’ Law (cont.)

Charles’ Law Example b The volume of a gas at 20°C is 500ml. Find its volume at standard temperature if the pressure is held constant. b T 1 = 20°C +273 b V 1 = 500ml b T 2 = 0°C +273 b V 2 =?

Formula V 1 = V 2 T 1 T 2 b Plug in values b 500ml V 2 b 293K 273K b SolveV 2 = 273K x 500ml b 293K b V 2 = ml =

Gay Lussac’s Law b If the volume remains constant, the temperature and pressure vary directly b i.e. if Pressure ↑, then Temperature ↑. *And vice versa P 1 P 2 T 1 T 2 =

Pressure and Temperature (cont.)

Gay-Lussac’s Example b 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. b T 1 = 27°C +273 b P 1 = 12 atm b T 2 = 100°C +273 b P 2 =?

P 1 = P 2 T 1 T 2 b Plug in values b 12 atm P2 b 300K373K b SolveP 2 = 373K x 12atm b 300K b P 2 = atm =