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Kinetic Molecular Theory

- This theory (KMT) explains the effects of temp.

and pressure on matter through 3 basic

assumptions - All matter is composed of small particles.
- These particles are in constant random motion.
- All collisions are perfectly elastic.
- there is no change in the total kinetic energy of

the 2 particles before and after the collision. - assumed that the gas particles attraction for

each other is negligible - The motion of the particles varies w/ changes in

temperature, of particles, and particle mass.

Measuring Pressure of a Trapped Gas

Use a manometer device used to measure gas

pressure Open-armed manometer if gas end lower

than open end, Pgas Pair diff. in height of

Hg if gas end higher than open end, Pgas Pair

diff. in height of Hg Closed-armed manometer Pgas

difference in height of mercury

Barometer special closed-armed manometer

designed to measure air pressure. Developed by

Evangelista Torricelli (1644)

(No Transcript)

Torricelli Barometer

The air pushes down on the mercury in the dish.

The space above the mercury is nothing. So the

mercury rises to the point that the forces of air

pressure and gravity are equal. Normal

atmospheric pressure pushes the mercury column to

a height of 76.0 cm (760. mm). So 1.00 atm of

pressure 760. mmHg 760. Torr 101,325 Pa

101.325 kPa

The Maxwell-Boltzmann Distribution

(Kinetic Energy)

Fig. E07.4.1 The number of particles at speed v

varies with the absolute temperature, as the

shape of the curve changes. However, the

distribution really has the same profile the

distribution is pushed to the left and upward as

temperature decreases, and is pushed to the right

and down as the temperature increases.

Simple Gas Laws

Simple Gas Laws - Examples

1.53 dm3 of sulfur dioxide gas at 5.60 kPa is

contracted to 0.571 dm3. What is the new

pressure (in atm)?

Gas at 15.0 0C has a volume of 2.58 dm3. If the

gas is heated to 38.0 0C, what is the new volume?

A sample of diborane (B2H6) gas has a pressure of

345 torr at -15 0C and 3.48 dm3. If the

temperature of the gas is increased to 36 0C and

the pressure is increased to 0.632 atm, what is

the volume of the gas?

IDEAL GASES

In the early part of the 19th Century,

Amadeo Avogadro demonstrated the relationship

between the number of particles and gas volume.

As amount of gas increases volume increases

proportinally (at constant P and T)

that is, V/n a.

As a result of this, equal volumes of gases at

the same temperature and pressure have the same

What do we ignore w/ these?

number of particles.

At standard temperature and pressure (STP)

1 mol of any gas has a volume equal to

22.4 L

V k/P

Charles Law

Boyles Law

V bT

kba constant,

R

Avogadros Law

V an

T

n

R

Therefore,

V

R

(Tn/P),

or

P

V

THE IDEAL GAS LAW!!

Lets try a problem

A sample of hydrogen gas has a volume of 8.56 L

at 0 0C and 1140 mmHg. How many grams of gas are

present?

If you have 2L of H2(g) and 1L of O2(g), at the

same temperature and pressure, why is there twice

as much H2?

Because there are 2X as many particles.

If you mixed the two gases and the total pressure

of the mixture was 99 kPa, what is the partial

pressure of each gas?

O2 would be 33kPa.

H2 would be 66kPa,

This is

Daltons Law of Partial Pressures.

Do you remember what to do if a gas is collected

over water?

Magnesium metal reacts with aqueous HCl to

produce hydrogen gas. The gas is collected over

water at 25 0C and 747 mmHg and is found to have

a volume of 3.557 L. How many grams of Mg were

used in the reaction? n.b. Assume 100 yield.

Partial pressure of water at 298 K 23.8 mmHg

REAL GASES

An ideal gas is a hypothetical concept. No gas

exactly follows the Ideal Gas Law, though many do

at high temperatures and low pressures, i.e.

normal conditions.

As long as these conditions exist, the law works

well,

But at high pressures and/or low temperatures,

modifications must be made to the equation.

An equation for real gases was developed in 1873

by Johannes van der Waals using experimental

values.

Pobs a(n/Vi)2 x (Vobs nb) nRT

a is in

atm L2/mol2

b is in

L/mol