C HAP 12 G ASES S ECTION 2 Gas Laws

G AS L AWS Gas Laws are: mathematical relationships between the variables in a gaseous system.

T HE F OUR G AS L AW V ARIABLES ( SEE PREZI ) Pressure = P Volume = V Temperature = T Moles = n Each of the 4 variables must be accounted for, either varied or held constant.

M OLES : VARIED OR CONSTANT When Moles are held constant it means the container is closed. When Moles are varied the container is opened at some point.

V OLUME : VARIED OR CONSTANT When Volume is held constant, it usually means the container is rigid. When Volume is varied, the container has the ability to expand or contract. (examples: syringes, piston systems, balloons)

E QUATIONS WITH 2 MANIPULATED VARIABLES You need to know the relationship between the two variables- either DIRECT or INDIRECT (Inverse) You will have two situations with each of the two variables. Situation 1 and Situation 2 ALL Temperatures MUST be in KELVIN units, for gas law calculations.

B OYLES L AW P RESSURE AND V OLUME Indirect Relationship between P & V P x V = Constant Temperature and Moles are held constant. P 1 x V 1 = P 2 x V 2

C HARLES ’ S L AW : V OLUME & T EMP Direct Relationship between V and T V / T = constant Pressure and Moles are constant Temp Must be Kelvin V 1 = V 2 T 1 T 2

G AY -L USSAC ’ S L AW : P RESSURE AND T EMP Direct relationship between P and T P/T = constant Volume and Moles are held constant Temperatures Must be Kelvin P 1 = P 2 T 1 T 2

A VOGADRO ’ S L AW Direct Relationship between V & n Pressure and Temp are constant V 1 /n 1 = V 2 /n 2

E QUATIONS WITH MORE THAN 2 VARIABLES THAT CHANGE Combined Gas Law = 3 variables Ideal Gas Law = 4 variables

C OMBINED G AS L AW Variables P, V and T Constant = n = moles (closed container) P1 V1/T1 =P2 V2 / T2

I DEAL G AS L AW All four variables are varied. Only one situation at a time. The Universal Gas Constant relates all the different units = R R = L atm/ K mol Ideal Gas Law: PV = nRT

M OLAR M ASS AND I DEAL G AS L AW PV = nRT can be converted into a useful form: PV = g RT MM g = mass of the gas and MM = molar mass of the gas

L AB : H YDROGEN AND O XYGEN On your own paper: Title, purpose, Safety, Materials, Procedure, Data Tables.