Aim: How can we balance chemical reactions? Do Now: 1.Take out a calculator and reference tables. 2.Describe the difference between a physical and chemical change.

How are physical and chemical changes different? A physical change does not result in the formation of a new substance. Rather it results in a change in appearance. A chemical change produces materials that are chemically different from the original reactants. There are two parts to a chemical reaction. Reactants – the substance(s) that enter into a reaction. Products – the substance(s) that is produced by the reaction.

How to write a chemical reaction A chemical reaction can be written in two directions. It will always have an arrow meaning produces and may have a plus sign if there is more than one reactant or product. Example:

Endothermic –v- exothermic reactions Endothermic reactions require energy in order to occur. Exothermic reactions release energy when they occur. TType of Reaction Surrounding Temperature Potential Energy of Reactants Potential Energy of Products Value of Delta H (∆H)

What happens to the reactants when they become products? The law of conservation of mass – matter is neither created nor destroyed. In any chemical reaction, the numbers and kinds of atoms must remain the same through the reaction. How can we use this information? We can use this information to determine how much of a reactant or product will be present based on a balanced equation.

Simple steps to balancing a chemical equation 1.Take the given equation and draw boxes around the chemical formulas. Never change anything within those boxes. 2.Make an element inventory by creating a chart showing the name of the element, and how many atoms there are on each side of the equation. 3.Write numbers in front of the boxes until the inventory for each element is the same before and after the reaction (HINT: USE A PENCIL FOR THIS STEP. Sometimes you will have to change the numbers to make them equal on both sides).

Examples: ____ H 2 + _____ O 2 ____ H 2 O _____C 3 H 8 + ____ O 2 ____H 2 O + ____ CO 2

Some More Examples ____AgNO 3 + ___ LiOH ___ AgOH + ____ LiNO 3 ___CH 4 + ___ O 2 ___CO 2 + ___ H 2 O ___Mg + ____Mn 2 O 3 ___ MgO + ___Mn

Even More Examples ___ NaCl + ____ BeF 2 ____NaF + ____BeCl 2 ___FeCl 3 + ___Be 3 (PO 4 ) 2 ___BeCl 2 + ___FePO 4

Activity/Homework # Review Book Pages Copy and answer #35-43