1. Chemistry Notes: Chemical Reactions Chemistry 2014-2015

2. Balancing Equations W 12/10

3.  In a chemical reaction equation…  Reactants are written on the left and products are written on the right  Ex. NaOH + HCl  H 2 O + NaCl  Sodium hydroxide and hydrochloric acid are the reactants, water and sodium chloride are the products.  An arrow acts as the “equals sign” of the reaction equation, pointing from the reactants to the products. This arrow means “yields” or “produces”.

4. The numbers written in front of each reactant or product are called coefficients. A coefficient indicates how many atoms, molecules, or formula units of each substance are present in the reaction. If no coefficient is written, the coefficient is implied to be one. Ex. Al 2 (SO 4 ) 3 + 3 CaCl 2 2 AlCl 3 + 3 CaSO 4

5. Review  We can use the symbols (s), (l), (g), and (aq) to show that an element or compound is a solid, liquid, gas, or aqueous solution, respectively. For example, liquid water is written H 2 O(l) while ice is written H 2 O(s).

6.  The Law of Conservation of Mass states that matter cannot be created or destroyed, but it can be changed from one form to another or moved around. In a chemical reaction equation, this means that the number of atoms of each element have to be the same on the products side and the reactants side.

7.  Reactants: ____ atom(s) of carbon, ____ atom(s) of hydrogen, ____ atom(s) of oxygen  Products: ____ atom(s) of carbon, ____ atom(s) of hydrogen, ____ atom(s) of oxygen Ex. CH 4 + 2 O 2  CO 2 + 2 H 2 O

8.  Reactants: ____ atom(s) of aluminum, ____ sulfate ion(s), ____ atom(s) of calcium, ____ atom(s) of chlorine  Products: ____ atom(s) of aluminum, ____ sulfate ion(s), ____ atom(s) of calcium, ____ atom(s) of chlorine You can keep polyatomic ions grouped together— Ex Al 2 (SO 4 ) 3 + 3 CaCl 2 2 AlCl 3 + 3 CaSO 4

9.  In order to balance a chemical reaction equation, you write coefficients in front of each reactant/product until you have an equal number of each element or polyatomic ion on both sides of the equation.  Begin balancing with the most complicated-looking group.  Save the elemental (single elements) reactant and products for last, especially if it is hydrogen or oxygen.  If you get stuck, double the most complicated-looking group and try again.  Finally, make sure that all coefficients are in the lowest- possible ratio.  You cannot change subscripts in a chemical reaction equation.

10. ____ H 2 (g) + ____ O 2 (g)  ____ H 2 O (l) ____ AgNO 3 (aq) + _____Cu (s)  _____ Cu(NO 3 ) 2 (aq) + _____ Ag (s) ____ Al + _____ O 2  _____ Al 2 O 3 Practice Problems: Balance the following chemical reaction equations.