1. Which process represents fusion?

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2. Which process represents condensation?

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3. Which process represents vaporization?

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Kinetic Molecular Theory (KMT) of Gases

• KMT is a model to explain the behavior of gaseous particles and is based on extensive observations of the behavior of gases.

• Kinetic energy = energy of motion

• If a gas follows all the postulates of the the KMT it is said to be an ideal gas.

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A. Water at 98 °C

B. Ice at 0 °C

C. Steam at 105 °C

D. Water at 350 K

Postulates of the KMT

1. A gas is composed of particles (atoms or molecules). Between these particles is empty space and no attractive or repulsive forces exist between particles.

2. These particles move fast in constant random motion. They travel in a straight line until it bumps into something else. This allows them to fill their entire container

Postulates of the KMT

3. All collisions are elastic. This means that all kinetic energy is transferred without loss from one particle to another.

Gas Pressure• Gas pressure is caused by gas particle

colliding with a surface. More collisions = higher pressure.

• SI Unit for pressure is a Pascal (Pa)• Others

– mm Hg– atm

Barometer

• As atmospheric gas pushes on the pool of liquid it forces the column higher up the glass tube.

• Modern barometers have a metal diaphragm that gases collide with

Temperature• The average kinetic energy of a

collection of gas particles is directly proportional to the Kelvin temperature of the gas.

• As a substance is heated, some of the heat is stored within the particles (this does not raise the temperature)

• Some of the energy speeds up the movement of the particles – this increases the temperature.

Temperature• At absolute

zero (O Kelvin) all molecules stop moving.

• SI unit = Kelvin (K)

• K=°C +273

5) If a gas is measured to a temperature of 23°C, what is its temperature in Kelvin? A) 299 K B) 296 K C) 250 K D) -296 K

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A. Kinetic energy gradually increases to a maximum.

B. They become farther apart.

C. Their motion gradually decreases and eventually stops.

D. They begin to take up more space as they cool.

Vapor Pressure• The vapor pressure of a liquid is the pressure

of a vapor above its liquid (or solid) at equilibrium.– http://www.chem.purdue.edu/gchelp/liquids/vpress

.html

• Liquid Vapor (gas)• Rate of evaporation = Rate of condensation

Manometer

At equilibrium an equal number of molecules evaporate and condense. The rate is constant.

This is when we can measure the vapor pressure.

Height difference in column = vapor pressure in mm Hg

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• If this manometer was connected to a flask, what would the vapor pressure be of the liquid contained?A. 620 mm Hg

B. 300 mm Hg

C. 320 mm Hg

D. 450 mm Hg