Unit 4: Chemical Reactions

According to the College Board, "This unit explores chemical transformations of matter by building on the physical transformations studied in Unit 3. Chemical changes involve the making➡️⬅️ and breaking⬅️➡️ of chemical bonds. Many properties of a chemical system can be understood using the concepts of varying strengths of chemical bonds and weaker intermolecular interactions. When chemical changes occur, the new substances formed have properties that are distinguishable from the initial substance or substances.

Browse slides from the stream 'Stoichiometry (Part 3).'

Browse slides from the stream 'Introduction to Titrations.'

Browse slides from the stream 'Stoichiometry (Part 2) .'

Browse slides from the stream 'Stoichiometry (Part 1) .'

From electronic devices📱 to fizzy soda🥤, our world runs on chemical reactions. So what happens in chemical reactions? In a simplified definition, specific interactions with molecules result in the rearrangement of atoms to create new molecules. However, this magic✨ has restrictions, as will be discussed in the next sections.

When dealing with chemical reactions, it is important to understand that, at least for the case of AP Chemistry, the vast majority of them will be taking place in an aqueous solution, that is, dissolved in water💧. Therefore, we will not be dealing with molecules, but rather their constituent particles that are created when they dissolve.

Just as net ionic equations provide information about interactions with ions in aqueous solutions, chemical reaction equations are a great way to visually track physical changes and chemical reactions. However, before we can examine these equations to observe these changes, we need to learn how to properly set up the equation for a chemical reaction. In other words, we need to learn how to balance equations. If an equation isn’t balanced, our answers will be incorrect. But why is it bad if it’s unbalanced, and how can we learn to balance equations easily?🤔

Chemical equations show the products that the combination of reactants yield, but the equation doesn’t show how the reactants form those products. What we don’t see are the underlying chemical and physical changes that allow molecules to rearrange to change properties or create new substances.

In the previous section, we looked at qualitatively analyzing chemical reactions. Now, we’ll learn how to quantitatively analyze reactions using stoichiometry! It may seem like a lot of math at first, but once you do more practice, you’ll be more confident and become a stoichiometry master 👨‍🏫

Titrations are an experimental method🧪 used to analyze acid-base reactions. The image below shows a set up of the apparatus.

If you recall, precipitation reactions are one of the main three you should know for this unit. Let's review it once more!

The second main type of reaction that you learn in this unit is the acid-base neutralization reaction🍊.

The last type of reaction in this unit are oxidation-reduction reactions, commonly called redox. These reactions deal with the transferring➡️ of electrons, which causes molecules to change oxidation states.