II. Balancing Equations

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

B. 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”

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

Evidence of chemical change

All chemical reactions have two parts _____________- the substances you start with ______________- the substances you end up with The reactants turn into the products. ______________ ® _____________

Balanced Equation Atoms can’t be ________________ or _________________ All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation.

® O + C O C O O ________ + _______ ® ________ __________________________ What if it isn’t already?

® O + C C O O ___________+ ______ ® _________ We need one more oxygen in the products. Can’t change the formula, because it describes what is

Never Change a subscript to balance an equation. If you change the formula you are describing a different reaction. H2O is a different compound than H2O2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.

Example H2 + O2 ® H2O Make a table to keep track of where you are at

Examples AgNO3 + Cu ® Mg + N2 ® P + O2 ® Na + H2O ® CH4 + O2 ® Pb(NO3)2+ KI  Show your work on a separate sheet of paper

On a separate sheet of paper balance the equations Don’t Break the Law