1. Lesson 5.1 – States of Matter
Chemistry 1 Honors
Dr. J. Venables
Northwestern High School

2. A Comparison of Solids, Liquids, and Gases
Physical properties of substances are understood in terms of kinetic molecular theory:
Gases are highly compressible, assume shape and volume of container:
Gas molecules are far apart and do not interact much with each other.
Liquids are almost incompressible, assume the shape but not the volume of container:
Liquids molecules are held closer together than gas molecules, but not so rigidly that the molecules cannot slide past each other.

3. Solids are incompressible and have a definite shape and volume:
Solid molecules are packed closely together. The molecules are so rigidly packed that they cannot easily slide past each other.

5. London dispersion forces
Converting a gas into a liquid or solid requires the molecules to get closer to each other:
cool or compress.
Converting a solid into a liquid or gas requires the molecules to move further apart:
heat or reduce pressure.
The forces holding solids and liquids together are called intermolecular forces.
Hydrogen Bonds
Dipole-dipole forces
London dispersion forces

6. Phase Changes

7. Energy Changes Accompanying Phase Changes
All phase changes are possible under the right conditions.
The sequence
heat solid  melt  heat liquid  boil  heat gas
is endothermic.
cool gas  condense  cool liquid  freeze  cool solid
is exothermic.

8. Heating and Cooling Curves
Plot of temperature change versus heat added is a heating curve.
Plot of temperature change versus heat removed is a cooling curve.
During a phase change, adding heat causes no temperature change.
These points are used to calculate Hfus and Hvap.
Supercooling: When a liquid is cooled below its melting point and it still remains a liquid.
Achieved by keeping the temperature low and increasing kinetic energy to break intermolecular forces.

9. From origin to “a” =
From a to b =
From b to c =
From c to d =
From d up =

10. From origin to a = solid
From a to b = melting/freezing point
From b to c = liquid
From c to d = boiling/condensation point
From d up = gas

11. Vapor Pressure and Boiling Point
Liquids boil when the external pressure equals the vapor pressure.
Temperature of boiling point increases as pressure increases.
Two ways to get a liquid to boil: increase temperature or decrease pressure.
Pressure cookers operate at high pressure. At high pressure the boiling point of water is higher than at 1 atm. Therefore, there is a higher temperature at which the food is cooked, reducing the cooking time required.
Normal boiling point is the boiling point at 760 mmHg (1 atm).