By the end of the period, I will be able to…  Based on observations, determine whether a chemical reaction has occurred  Use appropriate terminology to describe chemical reactions  Write word, skeleton, and balanced chemical equations using the IUPAC nomenclature system 1

~ Word Equations ~ Skeleton Equations ~ Balanced Equations 2

Figure 1: The wax of this candle is undergoing both physical and chemical changes. Which change results in new substances? Which does not?

Change in Colour Change in Odour Production of new gases, vapours or solid (precipitate) Release or absorption of energy (light, heat, electricity, or sound) Difficult to Reverse

Word Equation Skeleton Equation Balanced Equation **Important that you can work back and forth between these types of chemical equations**

 Chemical Reaction – is a process in which substances interact, causing different substances with different properties to form  Reactant – a starting substance in a chemical reaction  Product – a substance that is formed in a chemical reaction  Chemical Equation – a condensed statement that expresses chemical change using symbols and chemical names or formulas 7

 A WORD EQUATION describes chemical change using the names of the reactants and products Example 1 Write the word equation for the reaction of methane gas a oxygen to form carbon dioxide and water. Methane + oxygen  carbon dioxide + water REACTANTS PRODUCTS

SymbolPurpose + Indicates that two or more reactants or products are involved → Shows the direction of the chemical change that is taking place. The arrow stands for yields or reacts to produce. ⇋ Indicates a reversible reaction (s) Identifies a solid state (l) Identifies a liquid state (g) Identifies a gas state (aq) Identifies an aqueous solution 9

 A SKELETON EQUATION is chemical equation in which the reactants and products in a chemical reaction are represented by the chemical formulas; their relative quantities are not included Word Equation Methane + oxygen  carbon dioxide + water Chemical Equation CH 4(g) + O 2(g)  CO 2(g) + H 2 O (g)

Problem  When solid sodium carbonate is added to an aqueous solution of hydrochloric acid, liquid water, carbon dioxide gas, and an aqueous solution of sodium chloride are formed.  What is the skeleton equation or this chemical reaction? 11

Determine the chemical formula for each substance. Include the state.  Solid sodium carbonate: Na 2 CO 3(s)  Aqueous solution of hydrochloric acid: HCl (aq)  Liquid water: H 2 O (l)  Carbon dioxide gas: CO 2(g)  Aqueous solution of sodium chloride: NaCl (aq) 12

 Na 2 CO 3(s) + HCl (aq)  H 2 O (l) + CO 2(g) + NaCl (aq) 13 Check Your Solution The reactants are written on the left side of the arrow, and the products are written on the right side. The chemical formula for each substance is written correctly. The physical state of each reactant and product is shown.

 A BALANCED CHEMICAL EQUATION is a statement that uses chemical formulas and coefficients to show the identities and ratios of the reactants and products in a chemical reaction Chemical Equation CH 4(g) + O 2(g)  CO 2(g) + H 2 O (g) Equation is NOT balanced  Why?

 COEFFICIENT in a balanced chemical equation, a positive number that is placed in front of a formula to show the relative number of particles of the substance that are involved in the reaction. CH 4(g) + 2 O 2(g)  CO 2(g) + 2 H 2 O (g) 15

 Did I write out the word equation?  Is the skeleton equation written correctly?  Chemical formulas correct – criss-cross rule?  Are the states included?  Are the reactants and products on the correct side of the yield arrow?  Is the skeleton equation already balanced?  If not balanced, add coefficients to balance  Double check  State type of reaction 16