The Law of Conservation of Mass
The Law of Conservation of Mass states that matter cannot be created or destroyed, although it can be rearranged.
Example: When making a cake, we begin with certain ingredients. All the atoms in those ingredients will still be present in the cake at the end. But the molecules can break apart and rearrange themselves into new molecules which makes a cake different than cake batter.
Example: When making a cake, we begin with certain ingredients. All the atoms in those ingredients will still be present in the cake at the end. But the molecules can break apart and rearrange themselves into new molecules which makes a cake different than cake batter.
Rearrangement of molecules
My reactants on the left have 4 hydrogen atoms and 2 oxygen molecules. My products on the right have 4 hydrogen atoms and 2 oxygen molecules as well. The Law of Conservation of Mass holds true. Nothing was created or destroyed, it was only rearranged into different molecules.
NOTE: Remember that the arrow does NOT mean "equals". The arrow means "reacts to form". My reactants are hydrogen gas and oxygen gas which are very different from my product of 2 water molecules.
NOTE: Remember that the arrow does NOT mean "equals". The arrow means "reacts to form". My reactants are hydrogen gas and oxygen gas which are very different from my product of 2 water molecules.
Balancing equations
You need to understand how to read a chemical equation. There are a lot of things to remember, so here we go!
A letter by itself just represents one atom of that element. A "C" alone is just one carbon atom.
A letter next to another letter means the two atoms are combined. So "CO" means 1 atom of carbon is attached to 1 atom of oxygen.
A subscript tells how many of an atom there is and it applies ONLY to the atom before it. It also signifies that those 2 similar atoms are attached. So O2 means 2 oxygen atoms attached. Remember, the subscript only applies to the letter directly before it. So "CO2" means there is only 1 carbon atom and 2 oxygen atoms. All are attached.
A coefficient (a number before a letter) tells us how many of the following molecules there are. So 3 CO2 means there are 3 molecules of CO2 (See picture above).
A letter by itself just represents one atom of that element. A "C" alone is just one carbon atom.
A letter next to another letter means the two atoms are combined. So "CO" means 1 atom of carbon is attached to 1 atom of oxygen.
A subscript tells how many of an atom there is and it applies ONLY to the atom before it. It also signifies that those 2 similar atoms are attached. So O2 means 2 oxygen atoms attached. Remember, the subscript only applies to the letter directly before it. So "CO2" means there is only 1 carbon atom and 2 oxygen atoms. All are attached.
A coefficient (a number before a letter) tells us how many of the following molecules there are. So 3 CO2 means there are 3 molecules of CO2 (See picture above).
Quicker way to calculate
You can calculate the amounts of each atom by multiplying the coefficient by the subscript. When there is not a coefficient or a subscript, just pretend there is a 1 there. Look at the picture to the left.
CH4 has no coefficient. So pretend there is a 1 in front of it. 1CH4.
The H has a subscript but the C does not so pretend that it has a 1 as well. 1C1H4.
Now multiply the coefficient by the subscript for each element.
1 x C1 = one Carbon atom
1 x H4 = four Hydrogen atoms
Do that for each molecule on each side of the arrow. There should be the same amount of each atom on both sides for the equation to be balanced. If it is not balanced then the reaction is IMPOSSIBLE.
CH4 has no coefficient. So pretend there is a 1 in front of it. 1CH4.
The H has a subscript but the C does not so pretend that it has a 1 as well. 1C1H4.
Now multiply the coefficient by the subscript for each element.
1 x C1 = one Carbon atom
1 x H4 = four Hydrogen atoms
Do that for each molecule on each side of the arrow. There should be the same amount of each atom on both sides for the equation to be balanced. If it is not balanced then the reaction is IMPOSSIBLE.