|Notes: 30 August
||Phone: x 5719
Law of Conservation of Energy: Energy is neither created
nor destroyed in chemical processes. The problem here of course
is - What is energy? Energy is the capacity to do work. So what's
work? Work occurs when an object (mass) is moved against a force.
Some common forms of energy important to our study include:
- Kinetic Energy (KE) - energy due to motion. KE = 1/2 mv2.
- Potential Energy (PE) - energy due to position.
Another form of energy we need to be familiar with is:
- Heat - energy transferred between objects because
of a difference in temperature.
- Heat vs. Temperature: heat tells us how much energy is held
(can be transferred from) and object or given mass of stuff.
Temperature on the other hand is a measure of the energy per
particle in a sample of matter. Thus for a gas temperature is
a measure of the average Kinetic Energy (KE) of the gas particles,
while the amount of energy we must add to the gas to achieve
this average KE is the heat.
- Note that most energy eventually ends up as heat (ex.: burning
gasoline to move a car - heat in exhaust, friction in tire deformation,
braking, etc.) or work (car is moved against its inertia).
Note that these forms of energy are readily interconverted.
Last time we looked at some gerneral properties of matter,
and explored the physical states of the non-radioactive elements.
Let's look at matter in a variety of forms and try to deduce some
thing about its make-up. Recall the states of matter.
States of Matter and Changes of State
Matter can exist in three states under earth-surface conditions:
- Solid: definite shape and volume (Crystals vs. super-cooled
liquids or glasses)
- Liquid: definite volume, but no defined shape - will fit
to container etc.
- Gas: no definite shape or volume - will fill whatever container
they are in.
A common form of matter exhibiting these states under lab conditions
is water. Let's look at water starting in its solid state and
observe its transitions. We'll use the following equipment:
- Heat source (bunsen burner)
- Test tube
So let's all melt some ice and observe what happens:
- Fill beaker with ice, measure temperature and weight
- Melt partially, measure temperature.
- Continue measuring temperature as ice is heated and melts.
- When ice completely melted, weigh again.
- Note temperature change as liquid water is heated.
- Note temperature as water boils.
- Hold a test tube containing ice above boiling water, NOT
in steam, and observe what happens.
What can you say about what has happened? e.g.:
- Do you think mass was conserved?
- Was the water changed?
- Is ice a true crystalline solid? Why or why not?
Matter and Atoms
Why do we think atoms exist?
Demo spectroscopes and gratings - rainbows vs. line spectra.
© R A Paselk
Last modified 30 August 2004