Chapter 6
Gases
6.6
The Combined Gas Law
1
Combined Gas Law
The combined gas law uses Boyle’s Law, Charles’ Law,
and Gay-Lussac’s Law (n is constant).
P1 V1 =
T1
P2 V2
T2
2
Combined Gas Law Calculation
A sample of helium gas has a volume of 0.180 L, a
pressure of 0.800 atm and a temperature of 29°C.
At what temperature (°C) will the helium have a
volume of 90.0 mL and a pressure of 3.20 atm (n is
constant)?
1. Set up Data Table
Conditions 1
Conditions 2
P1 = 0.800 atm
P2 = 3.20 atm
V1 = 0.180 L (180 mL)
V2 = 90.0 mL
T1 = 29°C + 273 = 302 K
T2 = ??
3
Combined Gas Law Calculation
(continued)
2. Solve for T2
P1 V1 =
T1
P2 V2
T2
T2 = T1 x P2 x V2
P1
V1
T2 = 302 K x 3.20 atm x 90.0 mL = 604 K
0.800 atm 180.0 mL
T2 = 604 K - 273 = 331 °C
4
Learning Check
A gas has a volume of 675 mL at 35°C and 0.850 atm
pressure. What is the volume(mL) of the gas at -95°C
and a pressure of 802 mm Hg (n constant)?
5
Solution
Conditions 1
T1 = 308 K
Data Table
Conditions 2
T2 = -95°C + 273 = 178K
V1 = 675 mL
V2 = ???
P1 = 646 mm Hg
P2 = 802 mm Hg
Solve for V2
V2 = V1 x P1 x T2
P2
T1
V2 = 675 mL x 646 mm Hg x 178K
802 mm Hg x 308K
= 314 mL
6