1. Chemical Reaction Equations

2. Evidence of Chemical Reactions A gas is produced. A permanent color change is observed. An energy change occurs. A precipitate is formed. –Solid produced from mixture of liquids 2

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5. Chemical Reaction 5 A process in which one or more substances is changed into one or more new substances is a chemical reaction reactantsproducts (rxn)

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7. A chemical equation uses chemical symbols to show what happens during a chemical reaction 7 3 ways of representing the reaction of H 2 with O 2 to form H 2 O 2 H 2 +O 2  2 H 2 O

8. Chemical Equations: Direction Mg + O 2 MgO The direction of equation arrow can vary reactantsproducts Mg + O 2 MgO productsreactants Mg + O 2 MgO equilibrium 8

9. Chemical Equations: States Mg + O 2 MgO The state of each substance may be denoted (s)(s)(g)(g)(s)(s) State Designations: (g) gas (l) liquid (s) solid (aq) aqueous (dissolved in water) 9

10. The Law of Conservation of Mass Matter can be neither created nor destroyed In any chemical rxn, the total mass of reactants = total mass of products In 1789, first demonstrated experimentally by the Lavoisiers Antoine Lavoisier (1743 – 1794) Marie-Anne Pierrette Paulze (1743 – 1794) During a chemical rxn atoms do not change, they merely rearrange 10

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12. Chemical Equations: Reading 12 2 Mg + O 2 2 MgO 2 atoms Mg + 1 molecule O 2 makes 2 formula units MgO 2 moles Mg + 1 mole O 2 makes 2 moles MgO 48.6 grams Mg + 32.0 grams O 2 makes 80.6 g MgO NOT 2 grams Mg + 1 gram O 2 makes 2 g MgO

13. Chemical Equations: Balancing Equations must obey the Law of Conservation of Mass Mg + O 2 MgO (s)(s)(g)(g)(s)(s) coefficients Whole number coefficients are added to ‘balance’ equations Mg + O 2 MgO (s)(s)(g)(g)(s)(s) 22 1 Mg + 2 O1 Mg + 1 O 13

14. 14 Balancing Chemical Equations 1.Write the correct formula(s) for the reactants on the left side and the correct formula(s) for the product(s) on the right side of the equation. Ethane reacts with oxygen to form carbon dioxide and water C 2 H 6 + O 2 CO 2 + H 2 O 2.Change the numbers in front of the formulas (coefficients) to make the number of atoms of each element the same on both sides of the equation. Do not change the subscripts. 2 C 2 H 6 NOT C 4 H 12

15. 15 Balancing Chemical Equations 3.Start by balancing those elements that appear in only one reactant and one product. C 2 H 6 + O 2 CO 2 + H 2 O start with C or H but not O 2 carbon on left 1 carbon on right multiply CO 2 by 2 C 2 H 6 + O 2 2CO 2 + H 2 O 6 hydrogen on left 2 hydrogen on right multiply H 2 O by 3 C 2 H 6 + O 2 2CO 2 + 3H 2 O

16. 16 Balancing Chemical Equations 4.Balance those elements that appear in two or more reactants or products. 2 oxygen on left 4 oxygen (2x2) C 2 H 6 + O 2 2 CO 2 + 3 H 2 O + 3 oxygen (3x1) multiply O 2 by 7 2 = 7 oxygen on right C 2 H 6 + O 2 2CO 2 + 3H 2 O 7 2 remove fraction multiply both sides by 2 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O Want Have

17. 17 Balancing Chemical Equations 5.Check to make sure that you have the same number of each type of atom on both sides of the equation. 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O ReactantsProducts 4 C 12 H 14 O 4 C 12 H 14 O 4 C (2 x 2)4 C 12 H (2 x 6)12 H (6 x 2) 14 O (7 x 2)14 O (4 x 2 + 6)

18. Balance the following rxn equations: 1. N 2 + H 2  NH 3 2. HCl + CaCO 3  CaCl 2 + H 2 O + CO 2 3. C 3 H 4 O + O 2  CO 2 + H 2 O 4. Na 2 S 2 O 3 + Fe(NO 3 ) 3  NaNO 3 + Fe 2 (S 2 O 3 ) 3 18

19. Balance the following rxn equations: 32 1. N 2 + 3 H 2  2 NH 3 2 2. 2 HCl + CaCO 3  CaCl 2 + H 2 O + CO 2 2764 3. 2 C 3 H 4 O + 7 O 2  6 CO 2 + 4 H 2 O 32 4. 3 Na 2 S 2 O 3 + 2 Fe(NO 3 ) 3 6  6 NaNO 3 + Fe 2 (S 2 O 3 ) 3 19

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21. Evidence of Chemical Reactions A gas is produced. A permanent color change is observed. An energy change occurs. A precipitate is formed. –Solid produced from mixture of liquids 21

22. Rxn Types 22 1)Synthesis 2)Decomposition 3)Single Replacement 4)Double Replacement 5)Combustion

23. Chemical Equations: Translating from English 23 EnglishSymbol “and”, “with”, “mixed”, “dissolve” + “produce”, “decompose”, “combust”, “burned”, “electrolyzed”, “form” “precipitate”, “suspension”, “turnings”, “pellet”, “ribbon” (s)(s) “molten” (l)(l) “solution”, “acid” (aq)

24. Synthesis 24 Combination of two or more substances to form one compound Ex: “Chlorine gas is passed over a piece of sodium metal, producing solid sodium chloride.” Cl 2 (g) + 2 Na (s)  2 NaCl (s)

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26. Decomposition 26 A compound is broken down into simpler substances (which usually requires energy) Ex: “Powdered ammonium dichromate is strongly heated, producing heat, nitrogen gas, water and chromium(III) oxide.” (NH 4 ) 2 Cr 2 O 7 (s)  N 2 (g) + 4 H 2 O (g) + Cr 2 O 3 (s)

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28. Single Replacement 28 (single displacement) One element is replaced by another in a compound. (compound is usually an ionic compound) Ex: “A piece of magnesium ribbon is dropped into hydrochloric acid generating hydrogen gas and aqueous magnesium chloride.” Mg (s) + 2 HCl (aq)  H 2 (g) + MgCl 2 (aq)

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30. Double Replacement 30 (double displacement) The elements (or ions) in two compounds are exchanged (compounds are usually an ionic compounds) Ex: “Sodium iodide and lead(II) nitrate solutions are mixed to produce lead(II) iodide precipitate.” 2 NaI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2 NaNO 3 (aq)

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32. Combustion 32 Molecular oxygen combines with a hydrocarbon to form carbon dioxide and water (hydrocarbon = molecule consisting mainly of carbon and hydrogen) Ex: “Liquid ethanol is burned in air.” C 2 H 5 OH (l) + 3 O 2 (g)  2 CO 2 (g) + 3 H 2 O (g)

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