Chapter Nine

1. Chapter Nine Chemical Reactions

2. Section One Reactions & Equations

3. Chemical Reactions • Chemical Reaction • The process by which the atoms of one or more substances are rearranged to form different substances

4. Chemical Reactions • Some reactions are hard to detect. • Many provide physical evidence. • Evidence for Chemical Reactions • Temperature change • Release energy in the form of heat and light • Absorb heat • Color change

5. Chemical Reactions • Evidence for Chemical Reactions cont’d. • Odor • Gas bubbles • Formation of solid

6. Representing Chemical Reactions • Equations • Statements used to represent chemical reactions • Reactants • The starting substance • Products • The substances formed during the reaction

7. Representing Chemical Reactions • Equations • Show direction in which the reaction progresses • Reactants  Products • Read as reactants yield products

8. Representing Chemical Reactions • Equations • Symbols

9. Representing Chemical Reactions • Word Equation • Uses elements and compounds full names • Lacks important information • Example • Reactant 1 + Reactant 2  Product 1 • Aluminum(s) + Bromine(l)  Aluminum bromide(s)

10. Representing Chemical Reactions • Skeleton Equation • Provides important information • Uses chemical formulas • Example • Al(s) + Br2(l)  AlBr3(s)

11. Representing Chemical Reactions • Practice writing a reaction between carbon and sulfur (which are solids), to form carbon disulfide (which is a liquid).

12. Homework • Practice Problems • #1, 2, 3 on page 284

13. How to Balance Chemical Equations

14. Why even bother, aren’t they right once they’re written? Law of Conservation of Mass • Within a chemical reaction, the mass of the products is the same as the mass of the reactants. Reactants Products

15. Look at it this way. . . • INGREDIENTS • 2 ¾ cups all-purpose flour • 1 teaspoon baking soda • ½ teaspoon baking powder • 1 cup butter, softened • 1 ½ cups white sugar • 1 egg • 1 teaspoon vanilla extract Just like Reactants Products

16. So how do we balance an equation? Follow these simple steps. . . • Identify a complete chemical equation. • Identify and draw boxes around all the chemical formulas. • Take an inventory of the elements. • Use the inventory in order to determine which numbers need to be written in front of the boxes, so that the inventory is balanced.

17. 1. Have a complete chemical equation. • For this example we will write an equation with: • ● sodium hydroxide • ● sulfuric acid • ● sodium sulfate • ● water • We should get something that looks like. . .

18. 2. Draw boxes around all the chemical formulas.

19. 3. Make an inventory of the elements.

20. 4. Use the inventory in order to determine which numbers need to be written in front of the boxes, so that the inventory is balanced. • How does writing a number in front of one of these boxes effect the balance of the equation? • When a number is written in front of a box, anything within that box is multiplied by that number.

21. 4. Use the inventory in order to determine which numbers need to be written in front of the boxes, so that the inventory is balanced. element is the same both before and after the reaction. So, looking at the inventory, what should we do?

22. 2 4. Use the inventory in order to determine which numbers need to be written in front of the boxes, so that the inventory is balanced. element is the same both before and after the reaction. Now that we put a 2 in front of the NaOH, let’s update our element inventory. Now what should we do?

23. 2 4. Use the inventory in order to determine which numbers need to be written in front of the boxes, so that the inventory is balanced. element is the same both before and after the reaction. 2 Once again, we must update our element inventory. We have successfully balanced the equation!

24. Problems You May Encounter • What happens when you do the inventory, and you find that there are three atoms of element X on the left side of the equation and two on the right. FeCl3 + Be3(PO4)2 BeCl2 + FePO4 • How can you make those match?

25. Problems You May Encounter • Find the least common multiple of those two numbers. • In the element X example, the least common multiple of two and three is six, so you'd put a “2" in front of the molecule on the left, and a “3" in front of the one on the right. 2FeCl3 + Be3(PO4)23BeCl2 + FePO4

26. Problems You May Encounter • Put the numbers in front of those two boxes which allow the inventory on both sides to match. • Element X will then match up, and you can use a new inventory to see what else needs to be done

27. Inventory Table 2FeCl3 + Be3(PO4)23BeCl2 + FePO4

28. Inventory Table 2FeCl3 + Be3(PO4)23BeCl2 + 2FePO4

29. Problems You May Encounter • What happens when the only way you can get a problem to work out is to make one of the numbers a decimal or fraction? • Find the largest molecule in the equation and stick a "2" in front of it. • Start the problem over.

30. Let’s try some problems. Is this equation balanced? Yes No

31. Let’s look at the equation again. Is this equation balanced? Yes No

32. Very Good! It’s not balanced!

33. Time for Inventory

34. Now what? 2

35. It’s Balanced!! 2 2

36. Group Work Problem Set 1 • NaNO3 +PbO  Pb(NO3)2 +Na2O • AgI + Fe2(CO3)3  FeI3 + Ag2CO3 • C2H4O2 + O2  CO2+H2O • ZnSO4 +Li2CO3  ZnCO3 +Li2SO4 • V2O5 +CaS  CaO + V2S5 Let’s see how we did!

37. Group Work Problem Set 2 • Mn(NO2)2 +BeCl2  Be(NO2)2 +MnCl2 • AgBr + GaPO4  Ag3PO4 +GaBr3 • H2SO4 +B(OH)3  B2(SO4)3 +H2O • S8 +O2  SO2 • Fe + AgNO3  Fe(NO3)2 +Ag Let’s see how we did!