1. Solid, Liquid, Gas
(a) Particles in solid (b) Particles in liquid (c) Particles in gas

2. Solid
H2O(s) Ice
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

3. Ice H2O(s) Ice Photograph of ice model Photograph of snowflakes
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

4. Liquid In a liquid H2O(l) Water molecules are in constant motion
there are appreciable
intermolecular forces
molecules are close
together
Liquids are almost
incompressible
Liquids do not fill the
container
some writing from Kotz (PowerPoint online)
H2O(l) Water
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

5. Gas
H2O(g) Steam
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

6. Liquids The two key properties we need to describe are
EVAPORATION and its opposite CONDENSATION
add energy and break intermolecular bonds
EVAPORATION
CONDENSATION
release energy and form intermolecular bonds

7. States of Matter
Solid, Liquid, Gas are the three states of matter we will deal with.
Plasma and Neutron star are also states of matter.
For more information about plasma and neutron stars try the following links:
Coalition for Plasma Science – What is plasma?
Neutron Stars and Pulsars – Introduction

8. Gas, Liquid, and Solid Gas Liquid Solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441

9. States of Matter Solid Liquid Gas Holds Shape Fixed Volume
In a solid the molecules are closely bound to one another by molecular forces. A solid holds its shape and the volume of a solid is fixed by the shape of the solid.
Liquid
In a liquid the molecular forces are weaker than in a solid. A liquid will take the shape of its container with a free surface in a gravitational field. In microgravity, a liquid forms a ball inside a free surface. Regardless of gravity, a liquid has a fixed volume.
Gas
In a gas the molecular forces are very weak. A gas fills its container, taking both the shape and the volume of the container
Solid
Liquid
Gas
heat
heat
Holds Shape
Fixed Volume
Shape of Container
Free Surface
Fixed Volume
Shape of Container
Volume of Container

10. Some Properties of Solids, Liquids, and Gases
Property Solid Liquid Gas
Shape Has definite shape Takes the shape of Takes the shape
the container of its container
Volume Has a definite volume Has a definite volume Fills the volume of
the container
Arrangement of Fixed, very close Random, close Random, far apart
Particles
Interactions between Very strong Strong Essentially none
particles
The three common phases (or states) of matter are gas, liquid, and solid
1. Gases
a. Have the lowest density of the three states of matter
b. Are highly compressible
c. Completely fill any container in which they are placed
d. Their intermolecular forces are weak
e. Molecules are constantly moving independently of the other molecules present
2. Solids
a. Dense
b. Rigid
c. Incompressible
d. Intermolecular forces are strong
e. Molecules locked in place
3. Liquids
b. Incompressible
c. Flow readily to adapt to the shape of the container
d. Sum of the intermolecular forces are between those of gases
and solids
• The state of a given substance depends strongly on conditions

11. Evaporation
To evaporate, molecules must have sufficient energy to break IM forces.
Molecules at the surface break away and become gas.
Only those with enough KE escape.
Breaking IM forces requires energy. The process of evaporation is endothermic.
Evaporation is a cooling process.
It requires heat.

12. Condensation Change from gas to liquid
Achieves a dynamic equilibrium with vaporization in a closed system.
What is a closed system?
A closed system means matter can’t go in or out. (put a cork in it)
What the heck is a “dynamic equilibrium?”
What is condensation?
Condensation is the formation of liquid drops from water vapor. It is the process which creates clouds, and so is necessary for rain and snow formation as well. Condensation usually occurs when a parcel of rising air expands and cools. If it cools enough, some of the water vapor molecules clump together faster than they are torn apart from their thermal energy. A very important part of this process is the release of the latent heat of condensation. This is the heat that was absorbed when the water was originally evaporated from the surface of the Earth. The heat removed from the surface through evaporation is released again up in the atmosphere when clouds form. This process keeps the Earth's climate cooler that it would otherwise be if there were no water. Another way in which condensation occurs is during the formation of dew.

13. Dynamic Equilibrium
When first sealed, the molecules gradually escape the surface of the liquid.
As the molecules build up above the liquid - some condense back to a liquid.
The rate at which the molecules evaporate and condense are equal.

14. Rate of Vaporization = Rate of Condensation
Dynamic Equilibrium
As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense.
Equilibrium is reached when:
Rate of Vaporization = Rate of Condensation
Molecules are constantly changing phase “dynamic”
The total amount of liquid and vapor remains constant “equilibrium”

15. Vaporization
Vaporization is an endothermic process - it requires heat.
Energy is required to overcome intermolecular forces
Responsible for cool earth
Why we sweat

16. Energy Changes Accompanying Phase Changes
Gas
Vaporization
Condensation
Sublimation
Deposition
Energy of system
Liquid
Melting
Freezing
Solid
Brown, LeMay, Bursten, Chemistry 2000, page 405

17. Thermochemistry
The study of the changes in heat energy that accompany chemical reactions and physical changes

18. Thermochemistry Heat Temperature a form of energy.
can be transferred between samples
heat flows from matter at a higher temperature to matter at a lower temperature
Temperature
a measure of the average kinetic energy of the particles in a sample.

19. Thermochemistry Units of Heat Joule (SI unit) calorie Calorie cal
the amount of energy required to raise the temperature of one gram of water one degree Celsius.
Calorie
Cal
a dietary calorie.
kilocalorie, kcal (1,000 calories)

20. Thermochemistry Enthalpy the heat content of a system represented by H
only changes in enthalpy can be measured
∴ ΔH is used

21. Thermochemistry Specific heat capacity, cp
the amount of energy required to raise the temperature of one gram of a substance one degree Celsius
used in equation
q = m x cp x ΔT

22. Thermochemistry q = m x cp x ΔT
note that in the Metric System, Joules are the unit of measure for heat.
Energy, or heat
(J)
Δ temp
(°C)
mass
(g)
specific heat
(J/g•°C)

23. Heat capacity, cp

24. q = m x cp x ΔT
A 45.0-gram sample of iron is heated from 25.0°C to 50.0°C. How much energy is required? (cp iron = J/g°C)
q = ?
m = 45.0 g
cp = J/g°C
ΔT = 50.0°C – 25.0°C = 25.0°C
q = m cp ΔT
q = 45.0g (0.449 J/g°C) (25.0°C) =
q = 505 J

25. 2. What is the specific heat capacity of an object if a 12
2. What is the specific heat capacity of an object if a 12.5-gram sample is heated from 12.0°C to 28.0°C using joules? q = J m = 12.5 g cp = ? ΔT = 28.0 – 12.0 = 16.0°C q = m cp ΔT