Balancing Chemical Equations Antoine Lavoisier discovered the law of conservation of mass, which states that in chemical reactions, mass is never lost or gained. On the atomic level, this means that we never gain or lose atoms of any particular element in a chemical reaction. In other words, in every chemical reaction, we must end with the same number of atoms of each element with which we started. Set-up: 1. Go to phet.colorado.edu and open the simulation Balancing Chemical Equations. 2. Click on the Introduction tab. 3. From the top right drop-down Tools menu, select the bar graph. We are going to methodically balance the equation for the creation of ammonia. Remember, the goal is to have the same number of each type of atom on both sides of the equation. First, add 1N2,1H2, and 1NH3. Below the current chemical equation, count how many atoms you have of each element and tally them below each element's symbol. Why is our chemical equation unbalanced? Add a molecule of H2 to the reactants. How many atoms of each element do we have now? NHNHH2N2+2H2NH3 Since we now have too many hydrogen atoms on the reactants side, add another NH3 molecule. Take another atomic inventory. INHH2N2+2H22NH3NH OK, this is starting to look hopeless. Let's add one more H2 molecule to the reactants side and take another atomic inventory. INHN2+3H22NH3NH Finally, we have the same number of nitrogen atoms on each side of the equation and the same number of hydrogen atoms on each side of the equation! The