Energy
Review – matter is defined as anything that has mass and volume – anything that
you can weigh and takes up space.
Is sunlight matter? Can you weight it? Does it take up space?
You can’t see the air in the room, but it does have mass and volume that could be
measured.
Sunlight is not matter; it’s energy.
Energy – the capacity to do work or give off heat
Forms of Energy:
Light energy
Heat energy
Electrical energy
Nuclear energy
Kinetic energy – the energy of motion
Potential energy – stored energy (the potential to move)
If I set a book on the edge of a table it has potential energy. If I push it off of the
table that potential energy is converted in to kinetic energy.
Name all of the sources of energy in the classroom: fluorescent lights, sunlight,
potential energy, kinetic energy, electricity, batteries…
A calorie is a unit of energy. We tend to associate calories with food, but they apply
to anything containing energy.
Specifically, a calorie is the amount of energy, or heat, it takes to raise the
temperature of 1 gram of water 1 degree Celsius (1.8 degrees Fahrenheit). One
calorie is equal to 4.184 joules, a common unit of energy used in the physical
sciences.
Most of us think of calories in relation to food, as in "This can of soda has 200
calories." It turns out that the calories on a food package are actually kilocalories
(1,000 calories = 1 kilocalorie). The word is sometimes capitalized to show the
difference, but usually not. A food calorie contains 4,184 joules. A can of soda
containing 200 food calories contains 200,000 regular calories. Other countries do
use joules to describe food energy.
The number of calories in a food is a measure of how much potential energy that
food possesses. A gram of carbohydrates has 4 calories, a gram of protein has 4
calories, and a gram of fat has 9 calories. Foods are a compilation of these three
building blocks. So if you know how many carbohydrates, fats and proteins are in
any given food, you know how many calories, or how much energy, that food
contains.
Temperature Notes
Let’s talk about temperature now. Temperature is not a measure of heat! It is the
measure of the average kinetic energy of the particles in a sample. Heat is the
amount of energy transferred between two objects of different temperatures. Think
about it – it takes more heat energy to melt a big block of ice than a small block of
ice, but they melt at the same temperature. Heat cannot be measured, only changes
in heat. We’ll come back to that.
As you know, we use a thermometer to measure temperature. There are three
different temperature scales that you might see used in chemistry.
Fahrenheit: This is the one that you’re probably most familiar with since it is used
in the USA. Water freezes at 32°F and boils at 212°F. The development of the
Fahrenheit scale was fairly arbitrary. One scientist who made very good
thermometers back in the 16th century was named Gabriel Fahrenheit. As a
consequence, his thermometers, and his temperature scale became widely used.
Celsius: You might have also seen this one. It is used in the rest of the world. Water
freezes at 0°C and boils at 100°C. This temperature scale was not arbitrary at all. A
Swedish astronomer named Anders Celsius developed it in the 16th century to be
more compatible with the metric system. He marked the temperatures where water
froze and boiled on a thermometer, and then divided the distance between the points
in to 100 even graduations.
Kelvin: This one is used a lot in chemistry, but not in every day life. As you might
guess, it was named after a man named Lord Kelvin. The Kelvin scale was built so
that there would not have to be any negative temperature measurements. An
increase of 1K is the same as an increase of 1°C. 0K is absolute zero – the
temperature where there is no heat present at all and the motion of all particles
ceases. This temperature has not been reached anywhere yet.
Conversion Factors:
K = °C + 273
°C = (°F – 32) * (5/9)
°F = °C * (9/5) + 32
Ex) Dry ice, solid carbon dioxide, sublimes at -78.5°C. What is this in Kelvin?
K = °C + 273 = -78.5°C + 273 = 194.5 K
Ex) Pure aspirin melts at 135°C. What is this in Kelvin?
K = °C + 273 = 135°C + 273 = 408 K
Ex) The temperature of the surface of the sun is about 6573 K. What is this in
Celsius?
°C = K - 273 = 6573 K - 273 = 6300 °C
Ex) Human body temperature is 98.6°F. What is this in Kelvin?
°F = (°C+ 32) * (9/5)  98.6 = (x + 32) * 9/5) = 22.8 °C
K = °C + 273 = 273 + 22.8 = 295.8K
Temperature Comparisons:
The lowest ever recorded temperature on Earth was about -130°F in Antarctica.
The highest ever recorded temperature on Earth was about 134°F in Death Valley.