NAME:_____________________

Do Now:Practice Balancing Chemical Equations

Chemical equations describe reactants (starting substances) and products (ending substances). They also show qualitative (kinds of elements) and quantitative (how many) changes in bonding when atoms are rearranged.

For example:When magnesium burns in air, magnesium combines with oxygen and a

compound called magnesium oxide is formed. This is written....

magnesium + oxygen ----> magnesium oxideUsing chemical symbols and formulas......

Mg + O2 ---> MgOThis is a skeleton equation showing reactants and products but it does not show what

ratio they are reacting. According to the skeleton equation, 2 atoms of oxygen react but only 1 atom remains as a product. What happened to the other oxygen atom? This skeleton equation must be balanced. Balanced equations illustrate principles of conservation of mass.

Rules for Balancing Equations1. Check the number of atoms of each element on both sides of the equation (Make a “tally” sheet). If the same polyatomic ion appears of both sides of the equation, it can be treated as one unit.

2. Determine which elements and/or ions are present in unequal quantities on the two sides of the equation. Place coefficients in front of the substances, as needed, until each element and/or ion is present in equal quantities on both sides of the equation.

3. Make sure that your coefficients are in the lowest possible ratio. Where no coefficient is written, it is understood that the coefficient is one.

Let’s try with the original equation following the rules outlined above.

____ Mg + _____ O2 ------ > ______ MgO

PRACTICE BALANCING THESE EQUATIONS:

A. ______H2 + _______ O2 -----> ______H2O

B. ______Al2O3 -----> ______Al + ______O2

C. _____NaBr + ______Cl2 ---- > ______NaCl + _____Br2

D. _____BaCl2 + ______KIO3 --- > _____Ba(IO3)2 + _____KCl

E. ____ Cu + _____S8 ----> ______Cu2S

F. silver oxide --> silver metal + oxygen gas

G. aluminum sulfate + barium chloride -> aluminum chloride + barium sulfate

H. iron metal + copper II nitrate -> iron II nitrate + copper metal