The Combined Gas Law When measured at STP, a quantity of gas has a volume of 500 dm3. What volume will it occupy at 0 oC and 93.3 kPa? (101.3 kPa) x (500 dm3) = (93.3 kPa) x (V2) 273 K 273 K (101.3) x (500) = (93.3) x (V2) P1 = 101.3 kPa T1 = 273 K V1 = 500 dm3 P2 = 93.3 kPa T2 = 0 oC + 273 = 273 K V2 = X dm3 V2 = 542.9 dm3

Gay-Lussac’s Law The pressure and absolute temperature (K) of a gas are directly related at constant mass & volume Temperature (K) Pressure (torr) P/T (torr/K) 248 691.6 2.79 273 760.0 2.78 298 828.4 373 1,041.2 P T Joseph Louis Gay-Lussac (1788-1850, France) His experiments led him to propose in 1808 the Law of Combining Volumes, which states that the volume of gases involved in a chemical reaction are in a small whole number ratio. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Gay-Lussac’s Law The pressure and absolute temperature (K) of a gas are directly related at constant mass & volume P T Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

V T PV T P T PV = k P1V1 T1 = P2V2 T2 P1V1T2 = P2V2T1 Combined Gas Law V T PV T P T PV = k (COMBINED GAS LAW) (Gay-Lussac’s LAW) (CHARLES’ LAW) (BOYLE’S LAW) P1V1 T1 = P2V2 T2 P1V1T2 = P2V2T1 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Gas Law Calculations V PV = k T = k PV = nRT PV T = k Boyle’s Law Charles’ Law V T = k P and V change n, R, T are constant Ideal Gas Law PV = nRT T and V change P, n, R are constant Gas Law Calculations P, V, and T change n and R are constant Combined Gas Law PV T = k