Phase Changes

Phase Change

It is a transition between solid, liquid, and gaseous phases typically involve large amounts of energy compared to the specific heat.

Latent Heat

Is the HEAT released or absorbed by a body during a change of state without change of temperature.

Energy is absorbed from the air to melt solid ice into liquid water without any change is temperature.

Energy is also absorbed to change water into steam without any change in temperature.

Heat of Fusion

Heat of Vaporization

Melting

Freezing

evaporation

condensation

Phase Change Diagram

Simple Recall

The change from solid to liquid is.

The change from liquid to solid.

Melting

Freezing

Simple Recall

The change from gas to liquid

The change from liquid to gas

Condensation

Vaporization

Simple Recall

The change from solid to gas.

The change from gas to solid.

Sublimation

Deposition

Heat of Phase Change

Nature demands that energy always be conserved: The heat lost by objects of decreasing temperature must be equal to the heat gained by objects of increasing temperature.

Calorimetry

..Or the state of measurement of exchanging quantities of heat

Here, if heat is added to a body, then the value is positive; and if the heat is taken from a body, then the value is negative. Since energy (in this

case heat) is always conserved, then:

Heat added (+) + Heat taken (-) = 0 Heat added = heat taken

Problem Solving

Given : m = 30g , m = 85g at 25 C ,T =5 C

Find : m

A glass weighing 30g contains 85g of water at 25o C. How much ice at 0 C will be needed to bring the temperature down to 5 C? The specific heat of glass is 0.16cal/g, and that of water is 1.00 cal/g.

O

water

O

glass mix

ice

O O

Problem Solving

Solution:Let H (heat absorbed by ice) ---

(m )(80cal/g) H (heat absorbed by melted ice) ---

(m )(1.00cal/g C )(25 C – 5 C) H (heat given off by glass) ---

(30 g)(0.16cal/g C )(25 C – 5 C) H (heat given off by water) ---

1

ice

2

ice.O

O O

3 . O O

4