Lecture PLUS Timberlake 2000 1

Ideal Gas Law

The equality for the four variables involved in Boyle’s Law, Charles’ Law, Gay-Lussac’s Law and Avogadro’s law can be written

PV = nRT

R = ideal gas constant

Lecture PLUS Timberlake 2000 2

Ideal Gases

Behave as described by the ideal gas equation; no real gas is actually ideal

Within a few %, ideal gas equation describes most real gases at room temperature and pressures of 1 atm or less

In real gases, particles attract each other reducing the pressure

Real gases behave more like ideal gases as pressure approaches zero.

Lecture PLUS Timberlake 2000 3

PV = nRT

R is known as the universal gas constant

Using STP conditions P V

R = PV = (1.00 atm)(22.4 L) nT (1unit) (273K)

n T

= 0.0821 L-atm

unit-K

Lecture PLUS Timberlake 2000 4

Learning Check G15

What is the value of R when the STP value for P is 760 mmHg?

Lecture PLUS Timberlake 2000 5

Solution G15

What is the value of R when the STP value for P is 760 mmHg?

R = PV = (760 mm Hg) (22.4 L)

nT (1mol) (273K)

= 62.4 L-mm Hg mol-K

Lecture PLUS Timberlake 2000 6

Learning Check G16

Dinitrogen monoxide (N2O), laughing gas, is used by dentists as an anesthetic. If 2.86 units of gas occupies a 20.0 L tank at 23°C, what is the pressure (mmHg) in the tank in the dentist office?

Lecture PLUS Timberlake 2000 7

Solution G16

Set up data for 3 of the 4 gas variables

Adjust to match the units of R

V = 20.0 L 20.0 L

T = 23°C + 273 296 K

n = 2.86 unit 2.86 unit

P = ? ?

Lecture PLUS Timberlake 2000 8

Rearrange ideal gas law for unknown P

P = nRT

V

Substitute values of n, R, T and V and solve for P

P = (2.86 unit)(62.4L-mmHg)(296 K)

(20.0 L) (K-unit)

= 2.64 x 103 mm Hg