Chemistry

We've looked at how atoms bond and the types of molecular structures they form.  Now it's time to write down the reactions to show how many atoms are reacting and what products result from those reactions.

If you'd like a quick overview of the key types of reactions, check out the ExplainersEnigma video.  Otherwise, continue onward!

A chemical equation involves the reactants, which are your starting materials.  The products are the materials that result from the reaction.  One simple example is the burning of natural gas — this is the combustion reaction between methane and oxygen.  When you burn methane with oxygen, this produces water and carbon dioxide:

CH4 + 2O2 → CO2 + 2H2O 

In this equation, notice the following components:

• plus signs (+) separate the individual reactants and products

• Coefficients are the numbers of each molecule (two oxygen molecules and two water molecules in this example)

• The Arrow shows the direction the reaction goes, from reactant to product.

Precipitation Reactions

Remember that section about solutions?  When we bring together different compounds in a liquid, sometimes you get a reaction rather than a simple mixture.  In a precipitation reaction, the liquids react and cause a solid to form.

Acid-Base Reactions

When you add an acid to water, it releases hydrogen ions (H+) into the solution.  Adding a base leads to increased hydroxide ions (OH-).  In an acid-base reaction, the H+ ions are exchanged between atoms and molecules to create different compounds.

Oxidation-Reduction (Redox) Reactions

The oxidation number indicates the effective charge of each atom within a molecule — essentially, how many extra electrons the atom has gained or lost from bonding with other atoms.  In oxidation-reduction reactions, the effective number of electrons changes, sometimes with dramatic results, such as in combustion reactions.  The term "oxidation" comes from oxygen — and oxygen is well known for fire and corrosion.

Stoichiometry: Calculating Reaction Quantities

Let's say you have a some quantity of charcoal for a barbecue, and you want to know how much air is needed to burn all that charcoal.  If you have the reaction formula, you can use that starting mass of carbon to determine how much mass of oxygen it will react with.

This is where moles really help.  Using the molar masses from your reaction, you can calculate just how much reactant is needed for a certain amount of product, or you can see how much product you'll get from the amount of reactants you've put together.

In the Ketzbook videos, we first look at the basic concept of stoichiometry, and then how to use masses in your calculations.

Limiting Reagents and Percent Yields

When you bring two reactants together, it's unlikely that everything will completely react.  Instead, you'll have some constraints:

• A Limiting Reactant is the reactant you don't have enough of.  So the reaction will use up all of limiting reactant, but some of the other reactants will still be left over.

• Percent Yield indicates the amount of product you actually get when compared to how much you could theoretically produce.