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Learning Goals

Learning Goals. 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.

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Learning Goals

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  1. Learning Goals 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

  2. Writing Chemical Equations ~ Word Equations ~ Skeleton Equations ~ Balanced Equations

  3. How do you know whether the change you are observing is a chemical or physical change?

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

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

  6. Representing Chemical Change Word Equation Skeleton Equation Balanced Equation **Important that you can work back and forth between these types of chemical equations**

  7. Describing Chemical Reactions • 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

  8. Writing Word Equations • 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

  9. Symbols Used in Chemical Equations

  10. Writing Skeleton Equations • A SKELETON EQUATIONis 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 CH4(g) + O2(g)  CO2(g) + H2O(g)

  11. PRACTICE – Writing Skeleton Equations 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?

  12. PRACTICE – Writing Skeleton Equations Determine the chemical formula for each substance. Include the state. • Solid sodium carbonate: Na2CO3(s) • Aqueous solution of hydrochloric acid: HCl(aq) • Liquid water: H2O(l) • Carbon dioxide gas: CO2(g) • Aqueous solution of sodium chloride: NaCl(aq)

  13. PRACTICE – Writing Skeleton Equations • Na2CO3(s) + HCl(aq) H2O(l) + CO2(g) + NaCl(aq) 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.

  14. Writing Balanced Chemical Equations • 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 CH4(g) + O2(g)  CO2(g) + H2O(g) Equation is NOT balanced  Why?

  15. 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. CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)

  16. Balanced Equations Success Criteria • 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

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