1. Today! Introduce Chapter 9 (LAST UNIT OF THE SEMESTER) Outlining – NOPE! Balancing Equations – YES!

2. Chapter 9 – Chemical Reactions and Equations

3. Learning Objectives: ■ Be able to balance chemical equations by applying the law of conservation of mass. ■ Be able to recognize synthesis, decomposition, single replacement, double replacement, and combustion.

4. What are the signs of a chemical reaction?

5. Why Do Reactions Occur Think back to what we know about atoms and specifically their electrons?

6. Reactants ―› Products Reactants:the substances that enter into the reaction Products:the substances that are produced by the reaction

7. Law of Conservation of Matter Conservation of Matter: in all chemical and physical changes, matter is neither created or destroyed ■ The total mass in a chemical reaction remains constant

8. Step 1: Balancing Equations Write the word equation that describes the reaction. iron + oxygen ―› iron (III) oxide

9. Step 2: Balancing Equations 2. Replace the words in the equation with symbols and formulas. Fe + O 2 ―› Fe 2 O 3

10. Step 3: Balancing Equations 3. Count the # of atoms of each element on both sides of the equation. Fe + O 2 ―› Fe 2 O 3

11. Step 4: Balancing Equations 4. Starting with elements that only occur in one substance on each side of the equation. Remember that changing the # of one element may alter elements that have already been balanced.

12. Breaking down the Notation of Chemical Equations 2H 2(g) + O 2(g)  2H 2 O (l)

13. Let’s try: CH 4 + O 2 ―› CO 2 + H 2 O

14. Never change a subscript to balance an equation. ■ If you change the formula you are describing a different reaction. ■ H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula ■ 2 NaCl is okay, Na2Cl is not.

15. Balancing Equations: Examples ■ H 2 + O 2 → H 2 O

16. Co + O 2 → Co 2 O 3

17. Pb(NO 3 ) 2 + K 2 S → PbS + KNO 3

18. C 2 H 6 + O 2 → H 2 O + CO 2

19. Tuesday 1/12/16 Learning Target: Learn to write formula equations from word problems.

20. Balance the following iron(II) chloride + sodium phosphate → sodium chloride + iron (II) phosphate FeCl 2 + Na 3 PO 4 → NaCl + Fe 3 (PO 4 ) 2

21. To Review – Chemical Equations A method of describing chemical reactions ■ Word Equations Calcium + Oxygen ―› Calcium Oxide ■ Formula Equations 2Ca + O 2 ―› 2 CaO the arrow → separates the reactants from the products

22. Completing the Chemical Equation Complete the chemical equation by describing the physical state of each substance: ■ Solid (s) ■ Liquid (l) ■ Gas (g) ■ Aqueous (aq)means dissolved in water

23. 1. Write the word equation 2. Write the balanced formula equation ■ Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.

24. 1. Write the word equation 2. Write the balanced formula equation ■ Nitric acid reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate.

25. Symbols used in equations Double arrow indicates a reversible reaction shows that heat is supplied to the reaction is used to indicate a catalyst is supplied, in this case, platinum. ∆ Mn

26. What is a catalyst? A substance that speeds up a reaction, without being changed or used up by the reaction. Enzymes are biological catalysts.

27. Five General Types of Chemical Reactions Direct Combination (Synthesis) Decomposition Single-Replacement Double-Replacement Combustion By knowing the type of reaction that is occurring, you can predict the products that will be formed.

28. I. Direct Combination Reactions (also called synthesis reactions). General form: A + B → AB (two reactants make a single product) A, B = elements or compounds AB = compound consisting of A and B ■ This is the only type of chemical reaction in which there is a single product formed. This single product is always more complex than the reactants.

29. Examples of Synthesis Reactions ■ calcium + oxygen yields calcium oxide 2Ca + O 2 → 2CaO ■ Notice: All equations show two (or more) reactants, but only one product. ■ http://www.ric.edu/ptiskus/reactions/Index.htm http://www.ric.edu/ptiskus/reactions/Index.htm

30. II. Decomposition Reactions General form: AB → A + B (one reactant makes two or more products) AB = compound A, B = elements or simpler compounds ▪This is the only type of chemical reaction in which there is a single reactant. This single reactant is always more complex than the products.

31. Decomposition Reactions: Examples ■ water yields hydrogen and oxygen 2H 2 O → 2H 2 + O 2 ■ marble (calcium carbonate) yields calcium oxide and carbon dioxide CaCO 3 → CaO + CO 2 ■ Notice: all equations show a single reactant decomposing into two (or more) products. ■ http://www.ric.edu/ptiskus/reactions/Index.htm http://www.ric.edu/ptiskus/reactions/Index.htm

32. Today ■ Look at Single-Replacement Reactions. ■ Do a “Single-Replacement Lab”

33. Single-Replacement Reactions ■ Copper metal and silver nitrate: Cu (s) + AgNO 3(aq) → Ag (s) + CuNO 3(aq) ■ What do you observe about the reaction? ■ What do you notice about the chemical equation?

34. Single-Replacement Reactions General Form: A + BX → AX + B (switch partners) AX, BX = ionic compounds A, B = Metals X = ion that switches partners *Metal ‘A’ must be more reactive than ‘B’ for this to occur

35. Single-Replacement Lab Today you will do the following: 1. Formulate a question for the lab 2. Formulate a hypothesis 3. Design procedures 4. Create a data table.

36. IV. Double-Replacement Reactions General form: AX + BY → AY + BX (Positive ions in two compounds are exchanged) A,B = positive ions X,Y = negative ions ■ This is the only type of chemical reaction with two compounds as reactants and two compounds as products.

37. Double Replacement Examples ■ ammonium carbonate and calcium chloride yield ammonium chloride and calcium chloride (NH 4 ) 2 CO 3(aq) + CaCl 2(aq) → NH 4 Cl (aq) + CaCO 3(s) ■ Notice: in this reaction, two ionic compounds exchange ions to form two new ionic compounds www.ric.edu/ptiskus/reactions/Index.htm

38. Rules of Double-Replacement Reactions ■ Reactants must be dissolved in water (releasing the ions). ■ Will occur if one of the products : is a molecule (covalent), a precipitate (solid comes out of solution), or an insoluble gas.

39. V. Combustion Reactions General Form: C x H y + O 2 → H 2 O + CO 2 (hydrocarbon and oxygen react to form carbon dioxide and water) ■ This is the only type of chemical reaction where something reacts with oxygen and forms carbon dioxide and water

40. Combustion Examples ▪Methane reacts with oxygen: CH 4 (methane) + O 2 → H 2 O + CO 2 ▪Gasohol reacts with oxygen: C 2 H 5 OH (ethanol) + O 2 → H 2 O + CO 2 ▪Notice: in both cases, water and carbon dioxide are the products. www.ric.edu/ptiskus/reactions/Index.htm