Balancing Equations So far the equations tell us who is reacting. Now we have to be able to tell how much.

Learning Objectives  Balance simple chemical equations.  Determine reactant and product Moles in a balanced chemical equation.  Determine the mass of reactants and products involved in a simple chemical equation. *

Balancing Equations  The Law of Conservation of Matter states that matter is neither created nor destroyed in a chemical reaction. Each element present in the reactants must still be there as products.  Ex. ___HCl + ___Na(OH)  ___H(OH) +___NaCl H – 2H – 2 Cl – 1 Na – 1 O – 1 When equations do not have the same number of each atom as reactants and products, they must be “balanced.”

Procedure for Balancing Equations 1.Count the number of each type of atom on each side of the equation, saving Hydrogen, Oxygen and any element by itself for last. 2. Change coefficients to change the number of each atom until the same number is present on each side of the equation. Do not insert numbers in the middle of a formula or change the subscript in a formula. 3. Repeat for each successive type of atom until all are balanced. Tip: If you reach a situation where an odd number of atoms exists on one side of the arrow and an even number on the other. Double the number of odd atoms and then finish your balancing. *

How to Balance….Not!  Aluminum reacts with Oxygen to form Aluminum Oxide ___Al + ___O 2 ---> ___Al 2 O 3  Do not change the subscripts in the compound formulas. _2_Al + ___O 2 ---> ___Al 2 O 2  Do not place numbers in the middle of a formula. _2_Al + _3_O 2 ---> ___Al 2 2O 3  If you use fractions in the equation, don’t leave them. _2_Al O 2 ---> ___Al 2 O 3  Correct equation would be: _4_Al + _3_O 2 ---> _2_Al 2 O 3 *

Determining Mole Ratios  The balanced equation gives the ratio of Moles of reactants and products involved in the chemical equation (i.e recipe).  To determine the mass of a reactant or product involved, simply multiply the number of Moles times the molecular weight/atomic mass of the reactant or product.  Example: 3H 2 + _N 2  2NH 3 The Mole Ratio is 3H 2 : 1N 2 : 2NH 3 or 3:1:2 The Atomic Weights are 3x (1.008 x2) ; 1x ( x2) ; and 2x ( x3) So, = ; the Law of Conservation of Mass is observed. *

Some Quick Practice ___KCl + ___MgO  ___K 2 O + ___MgCl 2 Balanced Equation: 2KCl + MgO  K 2 O + MgCl 2 Mole Ratios: 2:1:1:1 __NaNO 3 + __Al 2 O 3  __Al(NO 3 ) 3 + __Na 2 O Balanced Equation: 6NaNO 3 + Al 2 O 3  2Al(NO 3 ) 3 + 3Na 2 O Mole Rations: 6:1:2:3 *

Balancing Equations Homework In your book, do the assigned work on a single sheet of paper. Be sure to show all work.  p.166 #1-5  p.168 #1-5