2-2 Balancing Chemical Equations

In a chemical change the atoms and ions are rearranged to form new compounds with new properties. A chemical reaction occurs when one or more chemical changes happen at the same time. The original compounds are called reactants The new compounds that are made are called products Chemical reactions are represented by chemical equations.

Chemical Equations Word Equation: Nitrogen monoxide + oxygen  nitrogen dioxide Symbolic Equation: 2 NO(g) + O2(g)  2 NO2 (g) What the numbers (coefficients) mean: 2 molecules NO gas react with 1 molecule O2 gas to produce 2 molecules NO2 gas

Chemical Equations You must specify what state each compound in a chemical equation is in: (g) = gas (s) = solid (l) = liquid (aq) = aqueous (dissolved in water)

Example Equation 2 HCl + CaCO3  CaCl2 + CO2 + H2O Identify the reactant(s) Identify the product(s) How many molecules of reactants are there? How many molecules of products are there?

Law of Conservation of Mass The total mass of the reactants MUST equal the total mass of the products This is why equations must be BALANCED!

Balancing Equations For an equation to be balanced, there must be an equal number of each type of atom on both sides of the reaction arrow In other words, the number of reactant atoms MUST EQUAL the number of product atoms We use coefficients (or numbers in front of the chemical formula) in order to balance out the numbers

Balancing Equations When balancing, you start with a skeleton equation This is just the chemical formulas with no coefficients added in yet Example: CH4 + O2  H2O + CO2

Balancing Equations Count up the number of atoms on each side of the equation CH4 + O2  H2O + CO2 2. Add coefficients in front of the compounds until the equation is balanced.

Balancing Equations Order for balancing: Metals Non-Metals Oxygen Hydrogen You don’t HAVE to balance in this order, but I find it makes it easiest!

Balancing Equations Count up the number of atoms on each side of the equation CH4 + O2  H2O + CO2 2. Add coefficients in front of the compounds until the equation is balanced.

__Zn + __HCl  __H2 + __ZnCl2 Balancing Equations Try this one! __Zn + __HCl  __H2 + __ZnCl2

__Fe2O3 + __CO  __Fe + __CO2 Balancing Equations Try this one! __Fe2O3 + __CO  __Fe + __CO2

Balancing Equations Assignment: Practice problems page 211 Start working through the big balancing equations worksheet booklet!