Chemical reaction/ this came from http://www.chem4kids.com/files/react_intro.html
Chemical ReactionsLet's start with the idea of a reaction. In chemistry, a reaction happens when two or more molecules interact and the moluscues change. That's it. What molecules are they? How do they interact? What happens? The possibilities are infinite. When you are trying to understand reactions, imagine that you are working with the atoms . Imagine the building blocks are right in front of you on the table, instead of billions of reactions in your beaker. Sometimes we do this using our chemistry toys to help us visualize the movement of the atoms. There are a few key points you should know about chemical reactions:
A chemical change must occur. You start with one compound and turn it into another. That's an example of a chemical change. A steel garbage can rusting is a chemical reaction. That rusting happens because the iron (Fe) in the metal combines with oxygen (O2) in the atmosphere. When a refrigerator or air conditioner cools the air, there is no reaction between the air molecules. The change in temperature is a physical change. When you melt an ice cube, it is a physical change. When you put bleach in the washing machine to clean your clothes, a chemical change breaks up your stains.
Now that we know the how and why of chemical bonding, we can look at some chemical reactions. Chemical reactions happen all around us: when we light a match, start a car, eat dinner or walk the dog. A chemical reaction is the pathway by which two substances bond together. In fact we have already discussed several chemical reactions. One we have mentioned is the reaction of hydrogen with oxygen to form water. To write the chemical reaction you would place the reactants (the substances reacting) on the left with an arrow pointing to the the products (the substances being formed). Given this information, one might guess that the reaction to form water is written:However there are 2 problems with this chemical reaction. First, because atoms like to have full valence shells, single H or O atoms are rare (and unhappy) creatures. As we saw in the previous lesson, both hydrogen and oxygen react with themselves to form the molecules H2 and O2, respectively. These hydrogen and oxygen molecules are much more common. Given this correction, one might guess that the reaction looks like this:n the chemical reaction above, the number in front of the molecule (called a coefficient) indicates how many molecules participate in the reaction. A simulation of the reaction can be viewed by clicking below (the atoms are represented as spheres in the animation: red = hydrogen, blue = oxygen).