From middleschoolchemistry.com: 

Watch the BrainPop on Chemical Reactions and take the quiz afterwards...

In a chemical change, the atoms in the reactants rearrange themselves and bond together differently to form one or more new products with different characteristics than the reactants. When a new substance is formed, the change is called a chemical change.

In most chemical reactions, two or more substances, called reactants, interact to create different substances called products. 

**Demonstration:  Burning a candle, which is an example of a chemical reaction.** 

Write the following three questions and the answers in your notebook:

1) What are the reactants in this reaction?

2) What are the products in this reaction?

3) Why does the flame go out when you put a jar over the candle?

Read on for further explanation: 

1) & 2)  When a candle is burned, what do you think are the reactants in this chemical reaction? What are the products?

Surprise!  It’s the wax on the string and not so much the string itself that burns and keeps the candle burning.  The molecules that make up the wax combine with oxygen from the air to make the products carbon dioxide and water vapor.  It may seem strange that water is actually produced by combustion (burning) since we usually think about water putting out fires.  But, did you know that when you “burn” food in your bodies, you also produce carbon dioxide and water?

  3) If a glass jar was placed over the lit candle, what do you think will happen?  Why?

  Placing a jar over the candle limits the amount of oxygen in the air around the candle. Without enough oxygen to react with the wax, the chemical reaction cannot take place and the candle cannot burn.

  

  

When a candle burns for a while, it eventually gets smaller and smaller. Where does the candle wax go?

When a candle burns, the candle wax seems to “disappear.” It doesn’t really disappear, though: It reacts chemically, and the new products go into the air.

Write and answer these next questions in your notebook.

4) What is the chemical reaction / equation for a burning candle?

5) Where do the atoms come from that make the carbon dioxide and water on the right side of the equation?

Read on for further explanation: 

Candle wax is made of long molecules called paraffin.  Paraffin is made up of only carbon atoms and hydrogen atoms bonded together. Molecules made of only carbon and hydrogen are called hydrocarbons. We will use the simplest hydrocarbon (methane) as a model to show how the wax, or any other hydrocarbon, burns.

Click on this link to see how methane and oxygen react.:  combustion_of_methane.swf

Methane and oxygen are on the left side of the chemical equation and carbon dioxide and water on the right side. The molecules on the left side are the reactants and the ones on the right side are the products. When the candle was burning, the paraffin reacted with oxygen in the air to produce carbon dioxide and water, similar to the chemical reaction between methane and oxygen.

4) What is the chemical reaction / equation for a burning candle?

The chemical formula for methane is CH₄. This means that methane is made up of one carbon atom and four hydrogen atoms.  The other reactant is two molecules of oxygen gas.  Each molecule of oxygen gas is made up of two oxygen atoms bonded together.

5) Where do the atoms come from that make the carbon dioxide and the water on the right side of the equation?

The atoms in the products come from the atoms in the reactants. In a chemical reaction, bonds between atoms in the reactants are broken and the atoms rearrange and form new bonds to make the products.

What is a Chemical Reaction? Modeling Activity: