Do Now – April [2(10) + 3], 2009

1. Do Now – April [2(10) + 3], 2009 • Did you share your love for the Earth with anyone after school yesterday? If so, how? • What is a chemical reaction?

2. Agenda • Do Now/Announcements • How to represent chemical reactions • Types of chemical equations • Start balancing chemical equations • Work time • Exit Ticket

3. Objectives • SWBAT write skeleton equations from word equations. • SWBAT balance skeleton (chemical) equations.

4. Remember Chemical Reactions? What is a chemical reaction? A chemical reaction is a process by which atoms of one or more substances are rearranged to form different substances

5. What is a chemical equation? • A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction

6. Chemical Equations are like Cookbook Recipes • A chemical equation is similar to a cookbook recipe in that it shows how many units of each substance is required to give the desired result • It shows the combination of various elements and/or molecules and then the resulting elements and/or molecules

7. Chemical Equations or…Math? • Chemical equations are similar to algebraic equations in that the total number of atoms of each element on the left side must equal the number for that element on the right side A mathematical equation: x+2x=3x A chemical equation: C3H8 + 5 O2 3 CO2 + 4 H20

8. Parts of a Chemical Equation A chemical equation identifies the starting and finishing chemicals as reactants and products: reactants  products Example (combustion of propane) C3H8 + 5 O2 3 CO2 + 4 H20

9. 3 Types of Chemical Equations Word equations Skeleton equations Balanced equations

10. Solids, Liquids, Gases…and One More • The reactants and products can exist in 4 different forms (or phases) Solid (s) Liquid (l) Gas (g) In water/Aqueous (aq)

11. Word Equations • Word equations use words to show chemical reactions Example: Solid iron and chlorine gas react to form solid iron(III) chloride iron (s) + chlorine (g)  iron(III) chloride (s) • It’s like a short “chemical sentence” describing a chemical reaction!

12. Word Equations - Practice • Write the word equation for the following… • Solid magnesium and chlorine gas react to form solid magnesium chloride • The reaction of hydrogen gas and bromine gas yields hydrogen bromide gas • Aqueous sodium hydroxide reacts with aqueous hydrogen chloride to produce solid sodium chloride and aqueous dihydrogen monoxide.

13. Skeleton Equations • Skeleton equations use chemical formulas rather than words to identify products and reactants Example: Word: iron (s) + chlorine (g) --> iron(III) chloride (s) Think: What are the formulas for each part of the reaction? Iron = Fe, Chlorine gas = Cl2 Skeleton: Fe (s) + Cl2 (g) --> FeCl3 (s)

14. Skeleton Equations - Practice • Write the skeleton equations for the following… • hydrogen (g) + bromine (g) --> hydrogen bromide (g) • carbon monoxide (g) + oxygen (g) --> carbon dioxide (g) • potassium chlorate (s) --> potassium chloride (s) + oxygen (g) Chlorate is a polyatomic ion: (ClO3)-1

15. Balancing Equations: Chemical Reactions

16. Ca O O H H How molecules are symbolized Cl2 2 Cl 2 Cl2 • Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2 • Notice that the OH is a group • The 2 refers to both H and O

17. Chemical Equations and the Law of Conservation of Matter • Chemical equations shows how the law of conservation of matter is obeyed • The mass of atoms of REACTANTS must equal the mass of atoms of PRODUCTS • When Massreactants = Massproducts you have a balanced chemical equation

18. Balanced Chemical Equations Fe (s) + Cl2 (g) --> FeCl3 (s) NOT BALANCED! To balance an equation, you must determine the correct coefficient for chemical formulas in skeleton equation. A coefficient is a number in front of a reactant or product.

19. Balanced Chemical Equations Fe (s) + Cl2 (g) --> FeCl3 (s) NOT BALANCED! 2 Fe (s) + Cl2 (g) --> FeCl3 (s) 3 2 COEFFICIENTS BALANCED: 2 Fe and 6 Cl on each side!

20. Determine whether the following equations are balancedAre there the same number of atoms of each element on both sides of reaction? • 2 Al + HCl --> 3 AlCl3 + 3H2 • Ba(ClO3)2 --> BaCl2 + 2O2 • 3 Sn(SO4)2 + 4 K3PO4 --> Sn3(PO4)4 + 6 K2SO4 • C5H12 + 11 O2 --> 5 CO2 + 12 H2O TIP! Keep track of each element when counting the number of electrons!

21. Rules of Balancing • RULES: You cannot change the subscript! You cannot put a coefficient in the middle of a formula!

22. Reaction to Yield Water Unbalanced reaction:H2 + O2 H2O Correct, balanced equation: 2 H2 + O2 2 H2O Balanced equation, but coefficients not whole numbers:H2 + ½ O2 H20 Balanced, but its coefficients are not least whole numbers:4 H2 + 2 O2 4 H20

23. Balance equations by “inspection” Mg + O2 MgO 2Mg + O2 2MgO is correct Mg + ½O2 MgO is incorrect Mg2 + O2 2MgO is incorrect 4Mg + 2 O2 4MgO is incorrect Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. a) P4 + O2 P4O10 b) Li + H2O  H2+ LiOH c) Bi(NO3)3 + K2S Bi2S3 + KNO3 d) C2H6 + O2 CO2 + H2O 5 2 2 2 2 3 6 7 4 6

24. Balance these skeleton equations: a) Mg + HCl  MgCl2 + H2 b) Ca + N2 Ca3N2 c) NH4NO3 N2O + H2O d) BiCl3 + H2S  Bi2S3 + HCl e) C4H10 + O2 CO2 + H2O f) O2 + C6H12O6 CO2 + H2O g) NO2 + H2O  HNO3 + NO h) Cr2(SO4)3+ NaOH  Cr(OH)3+ Na2SO4

25. Balance these skeleton equations: a) Mg + 2HCl  MgCl2 + H2 b) 3Ca + N2 Ca3N2 c) NH4NO3 N2O + 2H2O d) 2BiCl3 + 3H2S  Bi2S3 + 6HCl e) 2C4H10 + 13O28CO2 + 10H2O f) 6O2 + C6H12O66CO2 + 6H2O g) 3NO2 + H2O 2HNO3 + NO h) Cr2(SO4)3+ 6NaOH  2Cr(OH)3+ 3Na2SO4

26. Exit Ticket Balance the following chemical equation: Al4C3 + H2O  CH4 + Al(OH)3