Gases and Pressure - Lecture Notes - General College Chemistry | CHE 201, Study notes of Chemistry

Download Gases and Pressure - Lecture Notes - General College Chemistry | CHE 201 and more Study notes Chemistry in PDF only on Docsity!

Gases

Gases

Important Parameters:

V: volume

T: temperature

N: number of moles

P: pressure?

(P atm = h) mmHg

Atmospheric Pressure

Units of Pressure

1 mmHg (torr): is the pressure exerted by a

Column of Hg 1mm high at 0.00 C.

1 atm = 760 mmHg

= 760 torr

= 14.7 psi

A Flask Equipped with a Closed-Tube Manometer P gas = (h) mmHg

Gas Pressure

The Empirical Gas Laws

• (^) Boyle’s Law :

V  1/P P (constant moles and T)

f f i i

P  V  P  V or Animation: Microscopic illustration of Boyle’s law See Figure and Animation: Boyle’s Law) Go to 13

An Example

• (^) A sample of chlorine gas has a

volume of 1.8 L at 1.0 atm. If the

pressure increases to 4.0 atm (at

constant temperature), what would be

the new volume?

f f i i

using P  V  P  V

( 4. 0 atm ) ( 1. 0 atm) ( 1. 8 L ) P P V V f i i f     V 0. 45 L

f



The Empirical Gas Laws

• (^) Charles’s Law :

V  T

abs

(constant moles and P)

or

i

i

f

f

T

V

T

V

 (constant moles and P)

(See Animation: Charles’s Law) (See Video: Liquid Nitrogen and Balloons) Go to 17

The Empirical Gas Laws

• (^) Combined Gas Law : In the event that all three parameters, P, V, and T, are changing, their combined relationship is defined as follows:

f

f f

i

i i

T

P V

T

P V

V

P

T

P

T

PV

T

cons t

, V T V

PV tan

An Example

• (^) A sample of carbon dioxide occupies 4.5 L

at 30°C and 650 mm Hg. What volume

would it occupy at 800 mm Hg and 200°C?

f f f i i i T P V T P V using 

( 800 mm Hg)( 303 K )

( 650 mm Hg)( 4. 5 L)( 473 K )

P T

PV T

V

f i i i f f

Vf  5. 7 L

The Empirical Gas Laws

Avogadro’s Law :

• (^) Equal volumes of any two gases at the same temperature and pressure contain the same number of molecules.
• (^) The volume of one mole of gas is called the molar gas volume , Vm.
• (^) Volumes of gases are often compared at standard temperature and pressure (STP), chosen to be 0oC and 1 atm pressure.

Avogadro’s Law

 V V n m   V  n

At STP,

V

m

 22 .4 L For all gases

The Ideal Gas Law and the Molar Gas Constant

R

PV

nT

1. 00 (atm) 22 .4 (L)

1 (mol) 273 (K)

PV nRT

R  0. 082 (L.atm) /P (mol.K)

For one mole of a gas at STP (P = 1atm, T=273K)

Using the Ideal Gas Law n PV RT mol m n M           15 7 32 5 32 5 . . . (atm) 50.0 (L) 0.082 (atm. L. mol. K ) 294 (K) (mol) 32.0 (g. mol ) m = 1.04 10 g O -1 -

3 2

Haw many grams of oxygen are there in a 50.0 L

gas cylinder at 21 C when the oxygen pressure

is 15.7 atm?

PV nRT atm L mol 0.082 K =  C + 273 Animations for ideal gas law