Gas Laws: IntroductionAt the conclusion of our time together, you should be able to:

1. List 5 properties of gases2. Identify the various parts of the kinetic

molecular theory3. Define pressure4. Convert pressure into 3 different units5. Define temperature6. Convert a temperature to Kelvin

Importance of Gases

Airbags fill with N2 gas in an accident.

Gas is generated by the decomposition of sodium azide, NaN3.

2 NaN3 ---> 2 Na + 3

N2

THREE STATES OF MATTERTHREE STATES OF MATTER

General Properties of Gases

There is a lot of “free” space in a gas.

Gases can be expanded infinitely.

Gases fill containers uniformly and completely.

Gases diffuse and mix rapidly.

To Review

Gases expand to fill their containers

Gases are fluid – they flow Gases have low density

1/1000 the density of the equivalent liquid or solid

Gases are compressible Gases effuse and diffuse

Properties of Gases

Gas properties can be modeled using math. This model depends on —

V = volume of the gas (L) T = temperature (K)

› ALL temperatures in the entire unit MUST be in Kelvin!!! No Exceptions!

n = amount (moles) P = pressure

(atmospheres)

Ideal Gases

Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory. Gases consist of tiny particles that

are far apart relative to their size. Collisions between gas particles and between particles and the walls of the container are elastic collisions

No kinetic energy is lost in elastic collisions

Ideal Gases (continued)

Gas particles are in constant, rapid motion. They therefore possess kinetic energy, the energy of motion

There are no forces of attraction between gas particles

The average kinetic energy of gas particles

depends on temperature, not on the identity of the particle.

Pressure

Is caused by the collisions of molecules with the walls of a container

Is equal to force/unit area SI units = Newton/meter2 = 1 Pascal (Pa) 1 atmosphere = 101,325 Pa 1 atmosphere = 1 atm = 760 mm Hg = 760

torr1 atm = 29.92 in Hg = 14.7 psi = 0.987 bar

= 10 m column of water.

Measuring Pressure

The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17th century.The device was called a “barometer”

  Baro = weight   Meter = measure

An Early Barometer

The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

PressureColumn height measures

Pressure of atmosphere

1 standard atmosphere (atm) *

= 760 mm Hg (or torr) *= 29.92 inches Hg *= 14.7 pounds/in2 (psi)= 101.325 kPa

(SI unit is PASCAL)

= about 34 feet of water!

And now, we pause for this commercial message from STP

OK, so it’s really not THIS kind of STP…

STP in chemistry stands for Standard Temperature and Pressure

Standard Pressure = 1 atm (or an equivalent)

Standard Temperature = 0 deg C (273 K)

STP allows us to compare amounts of gases between

different pressures and temperatures

STP allows us to compare amounts of gases between

different pressures and temperatures

Let’s Review:Standard Temperature and

Pressure“STP”

P = 1 atmosphere, 760 torr T = 0°C, 273 Kelvins The molar volume of an ideal gas is 22.42 liters at STP

Pressure Conversions

A. What is 475 mm Hg expressed in atm?

B. The pressure of a tire is measured as 29.4 psi.

What is this pressure in mm Hg? = 1.52 x 103 mm Hg

= 0.625 atm475 mm Hg x

29.4 psi x

1 atm760 mm Hg

760 mm Hg 14.7 psi

101.325 kPa 14.7 psi

Pressure Conversions – Your Turn

A. What is 2.00 atm expressed in torr?

B. The pressure of a tire is measured as 32.0 psi.

What is this pressure in kPa?

= 1520 torr2.00 atm x 760 torr 1 atm

= 221 kPa32.0 psi x

Converting Celsius to Kelvin

Gas law problems involving temperature require that the temperature be in KELVINS!

Kelvins = C + 273

°C = Kelvins - 273