There are some specialty areas of Chemistry. You can learn about Electrochemistry, Nuclear Chemistry, and Organic Chemistry. Here we want to talk a little about THERMOCHEMISTRY, the division of chemistry that deals with temperature in chemical reactions.
Some reactions give off a lot of heat while other use up a lot of heat. Have you ever seen those cold or heat packs in a first aid kit? There are chemicals in those bags that go through a reaction and make heat and cold. Chemists sat in labs with a bunch of chemicals and figured out the best ones to use for those packs.
The idea behind those reactions is that chemical bonds store a lot of energy. If you break those bonds, heat is given off. Sometimes when you make bonds, you need a lot of heat, that's when everything around the molecules gets really cold, the heat is sucked out of the area. Bonds are energy. Some store more energy than others.
Scientists use the Greek letter "DELTA" to say that there has been a change in something. In Thermochemistry they often use the symbol "Delta-T" which means there was a change in temperature.
WHAT ARE HEAT AND COLD?
It's a pretty simple idea. You think of heat, you think of fire. You think of cold, you think of an ice cube. It all has to do with KINETIC ENERGY. Heat has a lot of kinetic energy and gives it away, cold doesn't have much and absorbs energy from the area. Scientists measure heat in something called JOULES.
There are two kinds of heat in chemistry. The first is caused by PHYSICAL ACTIVITY. As you get more kinetic energy, there is more activity in the system. This extra activity makes more COLLISIONS occur. It is the collisions which are heat (like when you increase the pressure in a system). The second type of heat is caused by CHEMICAL PROCESSES. Instead of exciting a system and feeling the heat, chemical bonds are broken and energy is released. The release in energy charges up the system and the molecules bounce around faster, resulting in that physical activity we just talked about.
HEAT AND THE ENERGY AROUND YOU
There is energy all around us. Just like MATTER is all around us. Usually you will feel this energy as heat. Let's say it's really hot out today. Why is it hot? One big reason is that there is a lot of heat coming from the Sun. The Sun is a big furnace, and that furnace heats the earth. When the Sun is really bright, it transmits energy to the atoms and molecules in the air and ground, making them heat up. That is why you feel hotter. The Sun makes your molecules more excited because of the energy hitting you.
How about when you burn a piece of wood? When you burn something you release the energy from the chemical bonds in the wood. Where did the energy come from? The sun. A plant needs the sun to grow. Light hits the plant and helps a process called PHOTOSYNTHESIS. The plant captures the energy and stores it in the chemical bonds. When you burn a piece of wood, you are releasing all of the energy stored up, and that energy is heat.
ABSOLUTELY LORD KELVIN
So this Irish guy started out as William Thompson but everyone knows him now as Lord Kelvin The Magnificent (we added the magnificent part). He did a whole lot of work on Thermodynamics.
But wait, there's more! He was the first guy to talk about Absolute Zero temperature where all molecular motion stops (1847). And even more! He worked on the first transatlantic cable for telecommunications (1854)!
He was even head of the department of physics at his university at 22 years old! But still, he couldn't comb his hair a lick. Go figure.