Conserving Mass in Chemical Reactions

Law of Conservation of Mass: In a chemical reaction, the total mass of the reactants is ALWAYS equal to the total mass of the products. It is also known that matter cannot be created or destroyed. It can only be changed from one form to another. What does this mean about matter, specifically atoms, in a chemical reaction?

In a chemical reaction, atoms are NOT changed! The mass of the reactants and products is always equal because the NUMBER and type of atoms in the reactants and products is equal In a chemical reaction, the atoms are simply re-arranged. Molecules may be broken apart and new bonds may form, but the atoms in the reactants are the same atoms in the products!

Think About It! The average piece of wood is made of many glucose (sugar) molecules all bound together. When glucose is burned (combined with oxygen) the word equation is: glucose + oxygen  carbon dioxide + water O—O + + Does it look to you as though there are the same types and numbers of atoms at the beginning of the reaction as there is at the end of the reaction?

Word equations do not tell us anything about the number of atoms involved in a chemical reaction. In order to have that type of information we need to look at a reaction’s chemical equation. The chemical equation is: C6H12O6 + 6O2 -----> 6CO2 + 6H2O (glucose)

Balancing Equations How to Make Atoms Equal in a Chemical Reaction: Step 1: Write the proper formula for each element and compound in the reaction. Step 2: Count each type of atom on the reactant side and on the product side

Step 3: Multiply each formula using a coefficient (large number IN FRONT of the formula) until both sides of the equation are equal. - When no coefficient is written, assume 1 - DO NOT balance by changing the formula! Step 4: Recount to make sure everything is balanced Step 5: Reduce all coefficients if possible