Pressure Conversions

• 1 atm = 1.01325 x 105 Pa

• 1 bar = 1 x 105 Pa

• 1 millibar (mb) = 100 Pa

• 1 atm = 1.01325 bar

• 1 atm = 760 torr

• 1 torr = 1 mm Hg

Change volume (V) and the pressure (P) will change(assuming that temperature and the number of molecules are constant)

Boyle’s Law

PV = constant

Pressure and Volume are inversely proportional

P1V1 = P2V2

A gas occupying a volume of 725mL at a pressure of 0.970 atm is allowed to expand at constant temperature until its pressure reaches 0.541 atm. What is the final volume?

(725 ml)(0.970 atm) = (V2)(0.541 atm)

V2 = 1300 ml or 1.30 L

Change the amount of gas (n) and the volume (V) will change(assuming that temperature and pressure constant)

Avogadro’s Law

n V

Number of Moles and Volume are proportional

V1 V2

n1 n2

=

Change the temperature (T) and the pressure (P) will change(assuming that the volume and number of moles are constant)

Gay-Lussac’s Law

T P

Temperature and Pressure are proportional

P1 P2

T1 T2

=

An aerosol can is under a pressure of 3.00 atm at 25C. Directions on the can caution the user to keep the can in a place where the temperature does not exceed 52C. What would the pressure of the gas in the aerosol can be at 52C?

3.00 atm X atm 298 K 325 K

=

X = 3.27 atm

Change the temperature (T) and the volume (V) will change(assuming that the pressure and number of moles are constant)

Charles’ Law

T V

Temperature and Pressure are proportional

V1 V2

T1 T2

=

A sample of neon gas has a volume of 752mL at 25C. What volume will the gas occupy at 50C if the pressure remains constant?

752 ml X ml 298 K 323 K

=

X = 815 ml

What we find is that everything is interrelated…

The combined Gas Law

n = constant

Such that P1V1 P2V2

T1 T2

PV T

=

A He filled balloon has a volume of 50.0L at 15C and 820mmHg. What volume will it occupy at 650mmHg and 10C?

(50.0 L)(820 mmHg) = (X L)(650 mmHg) (288 K) (283 K)

X = 62.0 L

n = constantPV T

By defining the constant we can convert the proportionality into “workable” equation

PV = nRT

R is a constant which changes according to units, See Table 8.1 on page 401

R = 0.08206 L.atm/mol.K R = 8.314 J/mol.K

Ideal Gas L

aw!

Ideal Gas Conditions

• Negligible Interactions

• Negligible Particle Size

• High Temperature

• Low Pressure

Standard Temperature and Pressure (STP)

0oC

1 atm

Under standard conditions, what is the volume of 1.00 mol of gas?

PV = nRT

(1 atm)( V ) = (1 mol)(0.08206 L.atm/mol.K)(273 K)

V = 22.4 L

How many moles of gas are in my 600 ml Pepsi bottle?(assume that the room temperature is 22oC)

PV = nRT

(1 atm)(0.6 L) (0.08206 L.atm/mol.K)(295 K)= n

n = 0.025 mols