Chemical reactions and stoichiometry

This course is a part of Chemistry, a 18-course Topic series from Khan Academy.

We are now going to delve into the heart of chemistry. We learn ways of representing molecules and how molecules react. To do this, we'll even think about "how many" of a molecule we have using a quantity called a "mole".

This course contains 5 segments:

Balancing chemical equations

We are now going to look at chemical reactions. But as we do, we need to make sure that atoms aren't magically appearing or disappearing. Put another way, we need to sure that we have the same number of each constituent atom in the product of the reaction as we do in the reactants (the molecules that react)!

Stoichiometry

Now we are going to draw the connections between balancing equations and what happens in the lab (where you actually have a certain mass of a compound).

Limiting reagent stoichiometry

In a reaction, you often have extra of one molecule (or too little of the other) so all the reactant doesn't react. We'll explore how to identify which reactant is limiting which is helpful in a whole series of scenarios.

Molecular composition

We'll now explore two different ways of representing what elements are in a molecule: molecular and empirical formulas. Molecular formulas actually represent the number of atoms in a molecule while empirical formulas show us the ratio of the constituents based on experiments. In order to help us connect these ideas, we'll also explore a quantity called the "mole". Just as a "dozen" represents 12 of something, a "mole" represents roughly 602,200,000,000,000,000,000,000 of something. This will help us think about mass composition of molecules.

Types of chemical reactions

In a chemical reaction, atoms get rearranged, combined and separated to form new substances. We will be learning about the different ways reactions can be classified, and the properties of different reaction types.