Hello everyone. Welcome back to our lectures. This chapter will focus on chemistry. Students either really like chemistry or they really don't. I had a bad chemistry teacher back in high school so that when I got to college chemistry I didn't do very well.
Fortunately, I had a good bunch of study buddies and we made it through just fine. This is general biology, however, so we won't go very deep. We need to know topics for future chapters.
Chemistry is defined as the study of matter and the changes matter undergoes, which we call chemical reactions. Matter is anything that has mass and volume. Mass is the amount of stuff in an object. Don't get that confused with weight.
Weight is the pull of gravity, very different than mass. Volume is the amount of space in an object. Think of a box, length, width, and height.
That's the volume of the box. There are three states of matter. Solid, liquid, and gas. Solids have a definite shape and definite volume.
Liquids have an indefinite or variable shape, but a definite volume. Gases have both an indefinite or variable shape and volume. How do you measure the shape of a liquid?
How do you measure the shape of a gas? You can't. But you can measure the volume.
Both liquids and gases take the shape of the containers they're in. If we explore water and its three states of matter, we can understand the terms that apply. Some of these you've heard before, and some of them you haven't.
Solid to liquid is melting. Liquid to solid is freezing. Liquid to gas is evaporation.
Those terms are familiar. Solid to gas is sublimation. Gas to solid and gas to liquid are both condensation. If you've ever played with dry ice, which is frozen CO2, it goes directly from a solid to a gas. If you put frozen ice into a pitcher, it's going to bubble white smoke.
Very, very cool. But one thing to remember, it's all water. and doesn't change the composition.
Chemical reactions are where one thing becomes something else. Milk becomes buttermilk. Carbs become alcohol.
Liquid eggs become solid eggs. There's a chemical change in the substance, not just a physical change. For all chemical reactions, you use an equation. Reactants are on the left side of the arrow because they react with each other.
And you can have one or five reactants. Products are on the right side because they are produced. Again, you can have one to five products.
The arrow in the middle can mean lots of things, but most of the time it means yields. You should know which side of the equation a substance belongs to because it will matter on a test question. If I ask you which product is in photosynthesis, or is this a reactant of cellular respiration, you need to know which side it belongs to.