The three main states of matter that we meet daily are: gas, liquid, and solid.

We will be looking at the first state of matter, gas.

Gases can be compressed, they expand to fill their containers. The volume of a gas is variable

This is model for the behavior of an ideal gas. It is useful for predicting the behavior of gases.

•Ideal gas particles are so small that they take up no volume compared to the total volume of the gas.

•Ideal gas particles are in constant, rapid, random motion, moving in straight lines in all directions till they collide with other particles.

•There are no attractive or repulsive forces between particles and all collisions are elastic.

•The average kinetic energy of the particles is directly proportional to the absolute temperature. ( in kelvins)

In this room right now are millions of gas molecules and atoms colliding with the walls, the floor, your face and each other.

Can you feel it?

Table 1: Average composition of the troposphere & lower stratosphereConstituent % by volume Natural formation Natural Depletion

NitrogenOxygenArgon

Carbon dioxideNeon

HeliumOzone

HydrogenMethaneKryptonXenon

78.0820.940.930.0350.00180.00050.000060.000050.00017tracetrace

UV reacting with O2

Lightning, soil bacteria

Our atmosphere is a mixture of gases that consist mainly of nitrogen, N2, and oxygen,O2.

Earth’s Atmosphere provides the perfect conditions for life on this planet. There is plenty of oxygen for respiration, it protects us from solar radiation and it moderates the planets temperature.

One property of gases is that they exert pressure.

The pressure exerted by the gas mixture we call air is called atmospheric pressure.

The atmosphere that surrounds Earth is a sea of air. It exerts a force on the surface of the planet.

Above you is a column of air that is exerting a force on you.

This pressure can be measured.

But why is air exerting pressure?

Why is air pressure important?It causes windCreates clouds and clear skiesAllows us to predict the weather

Atmospheric pressure can be measured using a barometer, invented in 1643 by Evangelista Torricelli.

This barometer was filled with mercury, Hg.

He found that at sea level atmospheric pressure could support a column of mercury 760mm high.

This pressure comes from the mass of air pulled toward the center of the earth by gravity. Changing weather conditions cause this pressure to vary. The height of the column of Hg is not always 760 mm.

Units of Pressure:

mm Hg (millimeters of mercury) torr

atm (standard atmosphere)

Pa (SI unit for pressure) pascal

1.000 atm = 760.00 mm Hg = 101,325 Pa

Engineers measure pressure in psi (pounds per square inch)

1.000 atm = 14.69 psi

1. The pressure of a tire is 28 psi, what is this in atm, torr, and pascals?

1.000 atm = 14.69 psi

28 psi x 1.000 atm /14.69 psi = 1.9 atm

1.000 atm = 760.0 torr

1.9 atm x 760.0 torr /1.000 atm = 1.4 x 10 3 torr

1.000 atm = 101,325 Pa

1.9 atm x 101,325 Pa / 1.000 atm = 1.9 x 10 5 Pa

Irish scientist Robert Boyle experimented with the relationship between pressure and volume of gases.

He set-up a J-shaped tube and added mercury to see what it did to the volume of a trapped gas.

As pressure increased volume decreases.

This relationship is inversely proportional, when one increases the other decreases.

P = pressure V = volume k = a constant at a specific temperature

Pressure times a volume equals a constant.

P1 V1 = k

P2 V2 = k

P1 V1 = k = P2 V2 therefore P1 V1 = P2 V2

So if you know P1, V1 and V2 you can calculate P2

P2 P1 V1

V2

If you have a gas at a pressure of 56 torr and a volume of 1.5L What will be the new volume (V2) if the pressure is increased to 150 torr?

= 1.5L x 56 torr /150 torr = 0.56LV2 V1 P1

P2

In an automobile, the cylinder volume is 0.725L. After the piston moves up, the volume is 0.075L. The fuel-air mixture initially has a pressure of 1.00atm. Calculate the pressure (P2) of the compressed fuel-air mixture, assuming that the temperature remains constant.

Initial Conditions Final ConditionsP1 = 1.00 atm P2 = ?

V1 = 0.725L V2 = 0.075L

P2 P1 V1

V2

1atm 0.725L

0.075L 9.7atm

French physicist Jacques Charles was the first to fill a balloon with hydrogen gas and make a solo flight.

He showed that the volume of a gas increases when the temperature increases (at a constant pressure)

Charles’s experimental results

As the temperature drops, the volume decreases. This is a linear relationship.

As you cool gases they eventually liquefy. If you extend (extrapolate) these straight lines you will find that they all to go a zero volume at -2730C. Zero degrees kelvin.

This temperature is called Absolute zero.

The closest we have got to absolute zero is 0.00001 K

V bT

V

Tb cons tan t

The direct proportional relationship between volume and temperature is represented by this equation.

This law holds if the gas is held a t a constant pressure.

A 2.0L sample of air is collected at 298 K and then cooled to 278 K. (The pressure is held constant at 1.0 atm)

Does the volume increase or decrease? What is the volume of air at 278 K?

VT

cons tan t

V1

T1

V2

T2

Initial Conditions Final ConditionsT1 = 298 K T2 = 278 KV1 = 2.0L V2 = ?

V 2 T2 V1

T1278K

2.0L

298K 1.9L

A sample of gas at 15 ° C (at 1atm) has a volume of 2.58L. The temperature is then raised to 38°C (at atm).

Does the volume of the gas increase of decrease?Calculate the new volume

Initial conditions Final conditions

T1 = 15C T2 = 38CV1 = 2.58 L V2 = ?

You must convert the temperature from °C into K

T1 = 15°C = 15 +273 = 288K T2 = 38°C = 38 +273 = 311K

V2 V1 T2

T1

2.58L 311K

288K 2.79L

Avogadro investigated the relationship between the volume of a gas and the number of moles present in the gas sample.

He found that as the number of moles is doubled (at constant temperature and pressure), the volume doubles.

Volume is directly proportional to the number of moles

V

na cons tan t

Suppose you have a 12.2 L sample containing 0.50 mol of oxygen gas, O2, at a pressure of 1 atm and a temperature of 25°C. If all of this O2 is converted to ozone, O3, at the same temperature and pressure, what will be the volume of the ozone formed?

3O2(g) 2O3(g)

1. Write a balanced equation for the reaction

2. Calculate the moles of O3 produced

0.50molO2 2molO3

3molO2

0.33molO3

Initial conditions Final conditions

n1 = 0.50 mol n2 = 0.33 mol

V1 = 12.2 L V2 = ?

V1

n1

V2

n2

V2 V1 n2

n1

12.2L 0.33mol0.50mol

8.1L

The volume decreases, because there are fewer molecules present in the gas after O2 is converted to O3.

The ideal gas law combines the three gas laws we have looked at so far.

V k

PV bT

V an

(at constant T and n)

(at constant P and n)

(at constant T and P)

Boyle’s law;

Charles’s law;

Avogardro’s law:

PV k or

Where k,b,and a are constants. So we can combine this three gas laws to form the ideal gas law.

V RTn

Por

PV nRT

PV nRT

R is the universal gas constant. When the pressure is expressed in atm and the volume in L, R always has the value of 0.08206 L atm / K mol

Temperature needs to be in Kelvin.

A gas that obeys this equation is said to be behaving ideally.

A sample of hydrogen gas, H2, has a volume of 8.56L at a temperature of 0°C and a pressure of 1.5 atm. Calculate the number of moles of H2 present in this gas sample.

P = 1.5 atm V = 8.56 L T = 0°C = 0 + 273 = 273K

PV = nRT

n PV

RT

(1.5atm)(8.56L)

(0.08206Latm

Kmol)(273K)

0.57mol