Chemical Reactions - Video Tutorials & Practice Problems

Chemical Reactions

In this video, we're going to begin our lesson on chemical reactions. Chemical reactions consist of the making or breaking of chemical bonds, leading to changes in matter. Every single chemical reaction has reactants and products. Now, reactants are going to be the starting material in a chemical reaction, so you can think of the reactants as the ingredients for the reaction. Then, of course, the products are going to be the ending material in a reaction. Let's take a look at our image down below, which shows a chemical reaction. On the left-hand side, we have these building blocks that are broken apart into smaller individual pieces. They're broken down. On the right, the building blocks are coming together to build a larger, more complex structure. The beginning of every chemical reaction starts with reactants. Reactants are, once again, the starting material in a chemical reaction. Over here on the right-hand side, we have the ending material. The ending material is going to be the products. Every chemical reaction is going to have reactants and a product, and the reactant is always found at the very beginning of a chemical reaction arrow, and the product is found at the very end of a chemical reaction arrow. We'll be able to talk about different types of chemical reactions as we move forward in our course, but for now, this concludes our introduction to chemical reactions as well as the difference between reactants and products. We'll get more practice as we move forward through our course. So, I'll see you all in our next video.

Types of Chemical Reactions

In this video, we're going to introduce 2 different types of chemical reactions. Chemical reactions are categorized into 2 groups based on their energy requirements. Those 2 groups are going to be listed down below, and we have 2 images to show these different groups of chemical reactions.

The first group is endergonic reactions, which require an input of energy. You can think the "en" in endergonic reactions stands for the "en" in entering the reaction, because energy needs to enter the reaction for endergonic reactions to occur. Just like a person entering a room, you can think of endergonic reactions requiring energy to enter the reaction. You can see the symbol on his shirt representing energy, indicating that the person coming into the room represents energy entering the reaction.

The second type of reaction you should know are exergonic reactions, which are practically the opposite of endergonic reactions. Instead of requiring an input of energy, they release energy into the environment. Exergonic reactions allow energy to exit the reaction. You can think the "ex" in exergonic reactions stands for the "ex" in exit the reaction. It's just like a person exiting the room through a door. You can see the energy symbol on his shirt, representing energy exiting the room.

Let's take a look at our example below to better understand the difference between endergonic and exergonic reactions. Notice that our image is broken up into 2 halves; on the left-hand side, we're showing you endergonic, larger, and more structured molecules. When you take a look at our image below, you see the broken-down building blocks on the left-hand side as the reactants, the starting material or ingredients for the reaction. By the end of the reaction, those starting materials have been built up into a larger, more complex structure that is more organized. This would be the product, and there is some building up occurring here in this endergonic reaction. Energy has to enter this system, as illustrated by the person entering and the energy coming into the chemical reaction.

Now, on the right-hand side, we are showing you exergonic reactions, used to break down substances into their smaller components. This time, we're starting the reaction with reactants that are larger, more complex, and built up. By the end of the reaction, the molecules are being broken down into their smaller individual components. In this exergonic reaction, energy is actually leaving the system. It is exiting the system. The "ex" in exergonic stands for energy exiting the system. When we look at the graph below, notice that the reactants this time have higher energy than the products, which have lower energy. Because the products have lower energy, it means that energy is exiting the system and being released into the environment.

You can see how inorganic and exergonic reactions are practically opposites. The cell can utilize both endergonic and exergonic reactions, and we'll be able to talk even more about these reactions as we move forward through our course. But for now, this concludes our introduction to inorganic and exergonic reactions, and I'll see you all in our next video.

Which of the following statements is true for all exergonic reactions?

• A. The products have more total energy than the reactants.
• B. The reaction proceeds with a net loss of free energy.
• C. The reaction goes only in a forward direction: all reactants will be converted to products.
• D. A net input of energy from the surroundings is required for the reactions to proceed.