Kinetic Molecular Theory of Gases

On earth, all forms of matter usually exist in one or more of three phases – solid, liquid, and/or gas.

Kinetic Molecular Theory of Gases A gas is a form of matter that has: (1) no definite shape and (2) no definite volume. A gas sample will take the shape and volume of the container that it occupies. The particles of a gas will always spread out and fill their container.

Kinetic Molecular Theory of Gases A gas sample will take the shape and volume of the container that it occupies.

Relative to the size of the container, gas particles are very small and are very far away from their nearest neighbor. Where is everyone ? Kinetic Molecular Theory of Gases

Gas particles are continually attracting each other. The attractions are stronger when the particles are closer and weaker when the particles are farther apart. I’m a little attracted to you. I have a strong-ish attraction for you. The larger the gas particles are, the more strongly they will attract each other. Kinetic Molecular Theory of Gases

As a gas particle is moving across the container in a straight line (translational motion), it can also be spinning (rotational motion) and wiggling (vibrational motion). Kinetic Molecular Theory of Gases

ZOOM If a gas is heated to a higher temperature, the individual gas particles will move faster. Ho hum If a gas is cooled to a lower temperature, the individual gas particles will move slower. Kinetic Molecular Theory of Gases

A real gas is composed of widely spaced particles that have a tiny volume. All of the real gas particles have very weak attractions for each other. A Real Gas

Kinetic Molecular Theory of Gases An ideal gas is composed of widely spaced particles that have NO volume. All of the ideal gas particles have NO attraction for each other. An Ideal Gas

Kinetic Molecular Theory of Gases The particles of real gas and ideal gas are widely separated and are in a state of continuous, random, rapid, straight-line motion. The temperature of a gas sample is due to the speed of its particles. The greater the average speed of the gas particles, the greater the gas temperature will be. As the temperature increases, the gas particles move faster!

Kinetic Molecular Theory of Gases When molecular collisions occur, kinetic energy may be transferred from one molecule to another. During this transfer of kinetic energy, none is lost or converted to heat (an elastic collision). Since all of the energy remains as energy of motion, the net total energy of the system remains constant.

Kinetic Molecular Theory of Gases Pressure results from collisions that the gas particles make with the walls of the container. Gas pressure is measured in units of atmosphere (atm) and kilopascals (kPa). The faster the gas particles collide into the walls of the container, the higher the pressure will be. Slow moving particles produce low internal pressures. Fast moving particles produce high internal pressures. BAM! Poof!

Kinetic Molecular Theory of Gases Some other units of pressure are Torr and mmHg (millimeters of mercury). 1 atm = kPa = Torr = mmHg. A very special temperature and pressure is called STP (standard temperature and pressure). STP = atm (atmosphere) and 273 K.

Kinetic Molecular Theory of Gases Ex. (1) What is the pressure mmHg in atm? ____________ = ____________ X mmHg atm mmHg X = atm

Kinetic Molecular Theory of Gases Ex. (2) What is the pressure 2.67 atm in kPa? ____________ = ____________ X 2.67 atm kPa atm X = 270. kPa

Kinetic Molecular Theory of Gases Ex. (3) What is the pressure 95.0 kPa in mmHg? ____________ = ____________ X 95.0 kPa mmHg kPa X = 713 mmHg

Ex. (4) Under what temperatures and pressures does a real gas behave most like an ideal gas and why? at high temp. the gas particles move faster and the attractive forces become less noticeable. Kinetic Molecular Theory of Gases real gas at low temp and/or high pressure real gas at high temp and/or low pressure a real gas at STP an ideal gas at STP High temp and low pressure because At low pressure the gas particles move apart and their volumes are less noticeable.

Kinetic Molecular Theory of Gases Ex. (5) Which of the real gases most behaves like and ideal gas at STP? (1) Kr (3) Ne (2) Ar(4) He Ex. (6) A gas in a container exerts pressure due to which of the following explanations? (1) When the gas particles collide with each other. (2) When the gas particles collide with the walls of the container. (3) When the gas particles collide with the walls of the container and with each other. (4) When enough of the gas particles are present to fill the container.