CHANGE OF PHASE

CHANGE OF PHASEMatter exists in three common phases: solid,

liquid and gas.

CHANGE OF PHASE• Matter can change from one phase(state) to

another.

• The phase of matter depends on pressure and temperature.

• Changes in phase usually involve transfer of energy.

CHANGE OF PHASE• Evaporation – change from liquid phase to

gas phase.

• Condensation - change from gas phase to liquid phase.

CHANGE OF PHASE• Air contains some water vapor. At any

temperature there is an upper limit to the amount of water vapor that the air can hold. When this limit is reached, we say that the air is saturated.

• Condensation - change from gas phase to liquid phase.

CHANGE OF PHASE• Relative humidity indicates how much

water vapor is in the air compared to the limit for that temperature.

CHANGE OF PHASE• Relative humidity indicates how much

water vapor is in the air compared to the limit for that temperature.

CHANGE OF PHASE• As warm air rises it expands. As it expands

it cools. As it cools it can hold less water, and the water condenses to form tiny droplets. These droplets form a cloud.

• Fog is a cloud forming near the ground.

CHANGE OF PHASE• Evaporation is a cooling process. As the

faster water molecules leave the liquid, slower molecules are left behind resulting in lowered temperature and cooling.

• Condensation is a warming process because faster moving molecules slow down and give up energy in the form of heat.

CHANGE OF PHASE• Evaporation occurs faster when the

surrounding air is has little moisture, as opposed to when the surrounding air has a great deal of moisture.

CHANGE OF PHASE• Evaporation occurs faster when the

surrounding air holds little moisture, as opposed to when the surrounding air holds a great deal of moisture.

CHANGE OF PHASE• Boiling takes place when liquid changes to

gas beneath the surface and forms bubbles. Evaporation on the other hand takes place only at the surface of the liquid.

CHANGE OF PHASE• In order for boiling to take place the

pressure of the vapor within the bubbles must overcome the pressure of the atmosphere. When the temperature of the liquid is great enough to accomplish this, we call that temperature the boiling point of the liquid.

CHANGE OF PHASE• At high elevations the boiling point of water

is lowered, and cooking times must be adjusted.

CHANGE OF PHASE• A pressure cooker maintains an elevated

pressure inside, and results in a higher cooking temperature.

CHANGE OF PHASE• When water (and other liquids) cools, its

molecules slow down until the forces between the molecules cause them to stop moving around, and they vibrate in place.

• At this point water undergoes a phase change from liquid to solid.

CHANGE OF PHASE

• Molecular structure of solid water

CHANGE OF PHASE• This ring molecular structure accounts for

the fact that ice is less dense than liquid water.

CHANGE OF PHASE• If water is placed in a vacuum container,

and all the air is pumped out, it will boil at room temperature. As the faster moving molecules leave the liquid, the slower moving molecules remain and the temperature of the remaining liquid drops until it freezes.

CHANGE OF PHASE(p344)

CHANGE OF PHASE• Regelation – If pressure is applied to ice the

ring structure is crushed, and the ice becomes liquid water again. Once the pressure is removed, the water refreezes. This process is called regelation.

CHANGE OF PHASE - Regelation

CHANGE OF PHASE• Energy and change of phase – As a

substance transitions from a more organized to a less organized state, energy(heat) is absorbed.

• Energy and change of phase – As a substance transitions from a less organized to a more organized state, energy(heat) is released.

CHANGE OF PHASE - Regelation

CHANGE OF PHASE• Latent heat of fusion – the amount of

energy needed to turn a kilogram of a material from solid to liquid at its melting temperature.

• Latent heat of vaporization – the amount of energy needed to turn a kilogram of a material from liquid to gas at its boiling temperature.

CHANGE OF PHASE