Chemical Reactions & Equations Chapter 8 Suggested Reading Pages 261 - 274

Chemical Reaction A process in which one or more substances are converted into new substances with different physical and chemical properties.

Reactants Products Reactant or Reagent – a substance that enters into a chemical reaction. Product – a substance that is produced by a chemical reaction.

Word Equations Read: Calcium reacts with oxygen to produce Oxide Calcium + Oxygen Read: Calcium reacts with oxygen to produce calcium oxide

Balancing Chemical Equations The number of atoms of each element MUST be the same before and after a chemical reaction.

Coefficients Whole numbers placed in front of the formula to balance the number of atoms on each side of the equation.

Formula Equations Unbalanced: Ca + O2 CaO 2Ca + O2 2CaO Coefficients

Coefficient  subscript = # of atoms Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make numbers equal. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance.

Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient. If an element appears more than once per side, balance it last. Balance polyatomic ions as single units. “1 SO4” instead of “1 S” and “4 O”

Example 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 3 3 2 2  1 1 2 3  2  6 Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 3 3 2 2  1 1 2 3  2  6 3  6   3