1. Word Equations A word equation is a shorthand way of explaining what happens in a chemical reaction When calcium carbonate reacts with hydrochloric acid a gas, carbon dioxide is given off. Water and a salt, calcium chloride are also formed in the reaction Can be shortened to Calcium carbonate + hydrochloric acid  carbon dioxide + calcium chloride + water An arrow is used to separate the reactants from the products

2. Now look at the following problem Can you identify the reactants? Can you identify the products? What information is not needed? Now look at section A of your worksheet. Can you write word equations for the 5 problems there? When calcium hydroxide reacts with hydrochloric acid in water, dissolved calcium chloride and water are formed. This reaction gives off heat

3. Simple Chemical Equations Word equations are good but they don’t give us much information about the atoms involved. Therefore we need to be able to convert word equations into formula equations. Calcium carbonate + hydrochloric acid  carbon dioxide + calcium chloride + water CaCO 3 + HCl  CO 2 + CaCl 2 + H 2 O We need to remember to use our cross over method and prefixes to help us work out the formulae of the compounds

4. Balanced Chemical Equations Now even though formula equations tell us about the atoms involved they don’t give us any information about the mole ratios involved in the reaction. Ca(OH) 2 + HCl  CaCl 2 + H 2 O If you look at this equation you can see that there is only one atom of chlorine on the reactant side but two on the product. Since one of the fundamental Laws of Science is that matter cannot be created or destroyed we need to make sure we have the same number of atoms of each element on both sides of the equation

5. Rules for Balancing Equations 1.An equation is only balanced when there are the same number of atoms of each element on both sides of the equation 2.We can only put numbers infront of the formulae. 3.We cannot change any subscript numbers 4.Both these things result in us changing the compounds reacting and our reaction. 5.If an equation isn’t balancing. Leave it. Go onto another problem and come back later and start from scratch

6. Ca(OH) 2 + HCl  CaCl 2 + H 2 O Step 1: List which atoms you have on each side of the equation and how many you have of them. Step 2: Pick an element which is not C, H, or O and try to get the same number of atoms on both side of the equation Step 3: Repeat until you are left with only C,H, and O unbalanced then attack them NB: Sometimes an equation only contains C, H, and O. In that case go for the most logical one of the 3 to start with Now look at section C of your worksheet and try to balance the equations.