Balancing Equations

1. Balancing Equations The Law of Conservation of Mass/Matter states that whenever matter changes, mass/matter cannot be created or destroyed. So this means that the mass before the reaction has to be the same as the mass after the reaction. (mass reactants = mass products)

2. Balancing Equations Due to the Law of Conservation of Mass each type of element needs to be the same amount before the reaction and after the reaction. But, you can’t change the elements or subscripts that participate in the reaction, so you must write a coefficient in front of (to the left of) some or all of the materials in the reaction to make sure every type of element has the same number of elements on each side of the reaction.

3. Balancing Equations Let’s look at an example: Element A will bond with element B in the chemical reaction below: A2 + B2 AB2 Are there the same amount of A’s on the left as there are on the right??? NO!!! So, this goes against the LAW!!! We must balance this equation!!! How can we make there be the same # of each element on both sides???

4. Step By Step… 1. Draw a line down the center (from the arrow). 2. Take an inventory of the elements on both sides of the line. 3. Identify where you are short elements. 4. Draw lines where you can put coefficients and figure out what coefficient you need to multiply the element that is short by to get it to equal the other side. (Start with COMPOUNDS FIRST) 5. Repeat steps 2-4 until ALL elements are equal on both sides of the equation!!!

5. Balancing EquationsLet’s practice… 1.) Al + Br2 AlBr3 2.) H2 + O2 H2O 3.) Na + Cl2 NaCl 4.) Fe + O2 Fe2O3 5.) P4 + O2 P2O5

6. Balancing EquationsLet’s practice ANSWERS… 1.) 2Al + 3Br22AlBr3 2.) 2H2 + O22H2O 3.) 2Na + Cl22NaCl 4.) 4Fe + 3O2 2Fe2O3 5.) P4 + 5O22P2O5