1 Gas Laws

STP 2 Standard Temperature and Pressure 0°C and 1 atm

Boyle’s Law At a constant temperature pressure and volume are inversely related. As one goes up the other goes down P x V = K(K is some constant) Easier to use P 1 V 1 =P 2 V 2

P V

Examples A balloon is filled with 25 L of air at 1.0 atm pressure. If the pressure is change to 1.5 atm what is the new volume?

Charles’ Law The volume of a gas is directly proportional to the Kelvin temperature if the pressure is held constant. V/T= K (K is some constant) V 1 /T 1 = V 2 /T 2

V T

Absolute Zero 8 If data of T and V is extrapolated to the temp where volume is zero, the temp is –273.15°C This temp is where volume collapses – all atomic and subatomic motion stops

Examples What is the temperature of a gas that is expanded from 2.5 L at 25ºC to 4.1L at constant pressure.

Gay Lussac’s Law The temperature and the pressure of a gas are directly related at constant volume. P/T = K (K is some constant) P 1 /T 1 = P 2 /T 2

P T

Examples What is the pressure inside a can of deodorant that starts at 25ºC and 1.2 atm if the temperature is raised to 100ºC?

Putting the pieces together The Combined Gas Law Deals with the situation where only the number of molecules stays constant. (P 1 x V 1 )/T 1 = (P 2 x V 2 )/T 2.

Examples If 6.2 L of gas at 723 mm Hg at 21ºC is compressed to 2.2 L at 4117 mm Hg, what is the temperature of the gas?

Avogadro’s Law 15 The volume of a gas is directly proportional to the number of moles (n) V 1 /n 1 = V 2 /n 2 Example: A 12.2 L sample containing 0.50 mole of oxygen gas (O 2 ) is converted to ozone (O 3 ) at the same temperature and pressure. What is the volume of the ozone gas?

The Ideal Gas Law P V = n R T Pressure times Volume equals the number of moles times the Ideal Gas Constant (R) times the temperature in Kelvin. This time R does not depend on anything, it is really constant R = (L atm)/(mol K)

Example 17 What mass of hydrogen gas will occupy a volume of 2.50 L at a pressure of 755 mmHg and a temperature of 28 o C?