Chemical Reactions

1. Chemical Reactions

2. Conservation of Matter • The law of conservation of mass says that matter cannot be created or destroyed. • Even during a chemical reaction, the mass of the things you put in must equal the mass of the things that are made during the reaction.

3. Conservation of Matter Activity • You must wear goggles during this experiment. • Follow directions carefully. • Group activity rules apply.

4. Group Activity Rules • You must stay in your assigned group at your table unless you have permission to move around the room. • No horseplay! • Any behavior issues will result in a 0 on the assignment and possibly a trip to the office.

5. Conservation of Matter • What this means is that the number of atoms of each element that go into a reaction must equal the number of atoms that come out of the reaction.

6. Conservation of Matter • Atoms are not created or destroyed during a chemical reaction. • Scientists know that there must be the same number of atoms on each side of a chemical equation.

7. Balancing Equations • To balance a chemical equation, you must add coefficients in front of the chemical formulas in the equation. • You cannot change or erase the subscripts.

8. Chemical Equations • Chemical equations show us what is happening during a chemical reaction. 2Mg + O2 2MgO • The elements or compound(s) on the left side are the reactants. • The elements or compound(s) on the right side are the product(s)

9. Chemical Equations • The coefficients show us how many of each molecule are reacted or produced in the reaction. • What does the arrow mean?

10. Candy Chemistry • We are going to look at what happens on an atomic level in a chemical reaction using colored marshmallows to represent the atoms of different elements and toothpicks to represent the bonds between atoms.

11. Balancing Reactions Activity • Each group will have one set of cards. • Separate the cards into three groups: • Numbers • +, arrow, reactants, products • Chemical compounds

12. Balancing Reactions Activity • Put the Reactants card on the left and put the cards for the reactant(s) below. • Put the arrow to the right of the reactants • Put the Products card on the right and put the cards for the product(s) below

13. Balancing Reactions Activity • Count the number of atoms for each of the elements on the Reactants side. • Write the symbols and numbers in the Reactants column in Table 1. • Count the number of atoms for each of the elements on the Products side. • Write the symbols and numbers in the Products column in Table 1.

14. Balancing Reactions Activity • Use the coefficients to make the numbers of atoms of each element equal on both sides (balanced). • When you have a balanced equation, • Write the symbols and NEW numbers in the Reactants column in Table 1. • Write the symbols and NEW numbers in the Products column in Table 1. • HINT: They should be equal!

15. Balancing Reactions Activity • Write the balanced equation (including reactants, product, and correct coefficients) in the balanced equation column on Table 1. • When you have the balanced equation, raise your hand, and I will check it off.

16. Types of Reactions

17. Partners Activity • How are people like chemicals in reactions? • Boy and girl are attracted to each other • Makes a new couple (compound) • Synthesis A + B  AB

18. Partners Activity • How are people like chemicals in reactions? • Boy and girl are no longer attracted to each other • Break up (makes separate compounds) • Decomposition AB  A + B

19. Partners Activity • How are people like chemicals in reactions? • Boy (or girl) is more attracted to another boy (or girl) • One replaces the other (new compound and single element) • Single Replacement AB + C  CB + A

20. Partners Activity • How are people like chemicals in reactions? • Boy and girl replace each other in couples • Two new couples (two new compounds) • Double Replacement AB + CD  AD + CB

21. Reaction Types Demonstration • Synthesis A + B  AB 2Mg + O2 2MgO • Single Replacement AB + C  CB + A 2HCl + 2Zn  2ZnCl + H2

22. Reaction Types Demonstration • Double Replacement AB + CD  AD + CB 2NaOH + CuCl2 2NaCl + Cu(OH)2 • Decomposition AB  A + B 2H2O2 2H2O + O2

23. “Brady Bunch” Diagram • Fold your paper in thirds horizontally and vertically • You should have nine rectangles (like this)

24. “Brady Bunch” Diagram • Write “Reaction Types” in the middle • Make a square with the name of each reaction type and leave a blank square between each one • Synthesis • Single Replacement • Double Replacement • Decomposition

25. “Brady Bunch” Diagram • In the square next to each reaction type, write an equation or a picture of what is happening for that type. • Either write the reaction type in the equation or picture square or draw an arrow from the reaction type.

26. Identifying Reaction Types • Look at the reactants and the products: • Does the reaction have two reactants combining to form one product? • Synthesis • Does the reaction have one reactant coming apart to form two products? • Decomposition

27. Identifying Reaction Types • Look at the reactants and the products: • Does the reaction have any reactants that contain only one element? • Single Replacement • Does the reaction have two reactants made up of two elements switching their ions to form two products? • Double Replacement

28. Identifying Reaction Types • Practice 3Pb + 2H3PO4 3H2 + Pb3(PO4)2 2H2 + O2  2H2O 2NaBr + Ca(OH)2  CaBr2 + 2NaOH NH4OH  NH3 + H2O

29. More Practice • Practice Fe + CuSO4 FeSO4 + Cu MgO + H2O  Mg(OH)2 2NaCl + Ca(OH)2  CaCl2 + 2NaOH CaCO3  CaO + CO2

30. More Practice • Balance and Classify by Type: HF + O2 H2O + F2 NH3 + H2O  NH4OH NaI + Pb(NO3)2  PbI2 + NaNO3 NaOCl  NaCl + O2