This document discusses intermolecular forces and phase changes in matter. It defines key terms like solid, liquid, gas, and phase changes. Phase changes occur when energy is added or removed from a substance, changing the molecular order from solid to liquid to gas. During phase changes, temperature remains constant as the added or removed energy goes toward breaking or forming intermolecular forces rather than increasing kinetic energy. Heating and cooling curves illustrate temperature changes during heating and cooling and phase changes.

1. INTERMOLECULAR
FORCES OF LIQUIDS
AND SOLIDS; PHASE
CHANGES

2. KEY TERMS
• Fluid- A gas or a liquid; a substance that can flow.
• Phase -A homogeneous part of a system in contact with other
parts of the system, but separated by well-defined boundaries.
• Solid -A phase of matter with definite shape and volume.
• Liquid -A phase of matter with definite volume but no definite
shape.
• Gas -A phase of matter with no definite shape or volume of its
own.

3. • Intermolecular forces -Intermolecular forces are attractive forces between
molecules.
• Phase changes - Transformations of matter from one phase to another.
• Melting -A phase change from solid to liquid.
• Vaporization -A phase change from liquid to gas. Sublimation A phase change
from solid to gas.
• Condensation -A phase change from gas to liquid.
• Freezing -A phase change from liquid to solid.
• Deposition -A phase change from gas to solid.
• Exothermic process -Process that gives off or release heat to the surroundings.

4. • Endothermic process- Process that absorbs heat from the surroundings.
• Specific heat of a substance - The amount of heat needed to raise the
temperature of 1 gram of a substance by 1 OC.

5. FOCUS QUESTION
•What makes a gas different
from a liquid or solid?

6. FOCUS QUESTION
•Why are some substances
gases at room temperature,
while others are not?

7. WHAT PHASE(S) OF
MATTER EXIST IN THE
FOLLOWING
IMAGES?

8. WHAT CAUSES PHASE CHANGE IN
MATTER?

9. PHASE CHANGES
•are transformations of matter from one physical
state to another. They occur when energy (usually
in the form of heat) is added or removed from a
substance. They are characterized by changes in
molecular order; molecules in the solid phase have
the greatest order, while those in the gas phase
have the greatest randomness or disorder.

10. WHAT CHANGES IN MOLECULAR ORDER
OCCUR DURING PHASE CHANGES?

11. SUMMARY OF
PHASE CHANGE

12. HOW DOES A CHANGE IN ENERGY
AFFECT PHASE CHANGES?
• Phase changes occur when heat is added or removed from a substance.
• When a substance is heated, the added energy is used by the substance in either of
two ways:
• a. The added heat increases the kinetic energy of the particles and the particles
move faster. The increase in kinetic energy is accompanied by an increase in
temperature.
• b. The added heat is used to break attractive forces between particles. There is no
observed increase in temperature when this happens. Often a change in the physical
appearance of the substance is observed, such as a phase change.

13. • c. Conversely, the removal or release of heat results in two ways:
• A decrease in kinetic energy of the particles. The motion of the particles slow down.
A decrease in temperature is observed.
• Forces of attraction are formed, and a phase change may occur. No change in
temperature is observed.

15. HEATING CURVE
•The change in temperature of a substance as
it is being heated can be shown in a graph
called the heating curve.

16. COOLING CURVE

17. • When heat change is accompanied by a change in temperature, a
change in kinetic energies of the particles in the substance is
occurring. The particles are either moving faster or slowing down.
• When temperature remains constant during heat change, the
particles move at the same speed. The heat added or removed is
involved in breaking or forming attractive forces. A phase change
occurs at this temperature: solid melts or liquid freezes at the
melting point, which is also the freezing point; liquid boils, or gas
condenses at the boiling point, which is also the condensation
point.