September 16, 2014
Balancing Equations
Chemical Equations
A chemical reaction occurs when elements and/or compounds interact to form new substances.
The substances that undergo a chemical change are called reactants and the substances that are formed in the chemical reaction are called the products.
Reactants à Products
Law of Conservation of Mass
This law states that matter cannot be created, or destroyed during a chemical reaction. All the atoms present in the reactants must also be present in the products. September 16, 2014
Balanced Chemical Equations
Based in the Law of Conservation of Mass, the same number of atoms of each element must appear on both sides of the equation in a balanced chemical equation.
Word Equation Identifies the reactants and products by name
Ex. Potassium + Iodine à Potassium Iodide
Skeleton Equation
Identifies the reactants and products by their molecular formula, including the state of the molecule (solid, liquid, gas, aqueous)
Ex. K (s) + I2 (g) à KI (s)
Balanced Equation Reflects the Law of Conservation of Mass and shows that
there are the same number of each kind of atom on each side of the equation
Ex. 2 K (s) + I2 (g) à 2 KI (s)
Steps in Balancing Chemical Equations
1. Make sure the skeleton chemical equation is written correctly. 2. For each element, count the number of atoms on each side of the equation. 3. If the atoms are not equal, you will have to balance the equation by changing the amounts of reactants or products. 4. Start with the molecules that have many elements, usually, leaving the elements (Cu, H2, etc.) until the end.
5. Add a coefficient in front of the chemical formula for any unbalanced elements. NEVER add, remove or change subscripts!
6. Move on to the next element and follow the same procedure until all the elements are balanced. 7. Remember you can only add coefficients in front of the chemical formulas. You cannot change any of the elements or subscripts in a chemical formula. 8. Count up the number of atoms again to check your answer
September 16, 2014
Balancing Chemical Equations Tutorial
http://www.wfu.edu/~ylwong/balanceeq/balanceq.html
September 16, 2014
Don't break the Law of Conservation of Mass!
http://www.youtube.com/watch?v=QjVYz00­Kxc