CHEMICAL CHANGE

1. CHEMICAL CHANGE

2. Chapter Seventeen: Chemical Change • 17.1 Chemical Reactions • 17.2 Balancing Equations • 17.3 Classifying Reactions

3. Chapter 17.1 Learning Goals • Describe how energy is involved in chemical changes. • Identify evidence that a chemical change has occurred. • Explain what happens during chemical reactions.

4. Key Question: How are atoms conserved in a chemical reaction? Investigation 17A Chemical Equations

5. 17.1 Chemical Reactions • A chemical reaction is the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances. • When you make pizza, which changes are physical and which are chemical changes?

6. 17.1 Chemical Reactions • The process of making pizza involves some physical changes (like chopping vegetables). • The processes used by yeast in the dough or by the gas stove to bake the pizza are chemical changes.

7. 17.1 Evidence of chemical change Four indicators of chemical change are: • Formation of new gas • Formation of new solid • Release of energy (heat or light) • Color change

9. 17.1 Products and reactants • In chemical reactions, you start with reactants that are combined to make products. • The reactants are the starting substances. • The products are the new substances which result from the chemical reaction.

11. 17.1 Reactants and products • In the reaction, methane (a natural gas) is burnedor combusted. • Some energy is added to get the reaction started.

13. 17.1 Reaction symbols • The small symbols in the parentheses (s, l, g, aq) next to each chemical formula indicate the phase of each substance in the reaction.

14. Chapter Seventeen: Chemical Change • 17.1 Chemical Reactions • 17.2 Balancing Equations • 17.3 Classifying Reactions

15. Chapter 17.2 Learning Goals • Relate a balanced chemical equation to the law of conservation of mass. • Determine the formula and molar masses of chemical compounds. • Write and balance chemical equations.

16. Key Question: How do scientists describe what happens in a chemical reaction? Investigation 17B Conservation of Mass

17. 17.2 Balancing Equations • Antoine Laurent Lavoisier, established an important principal based on his experiments with chemical reactions. • He stated that the total mass of the products of a reaction is equal to the total mass of the reactants. • The law of conservation of mass holds true for even a burning mass of wood.

18. 17.2 Balancing Equations • The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.

19. 17.2 Conservation of mass • Lavoisier showed that a closed system must be used when studying chemical reactions. • When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

20. 17.2 Formula mass • The sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.

21. 17.2 Avogadro’s Number • The Avogadro number was named in honor of Amedeo Avogadro who discovered that a mole of any gas under the same conditions has the same number of molecules. • Johann Josef Loschmidt, a German physicist, named and discovered the Avogadro number. • Loschmidt realized that a mole of any substance—be it a gas, liquid, or solid—contains 6.02 x 1023 atoms or molecules.

22. 17.2 Molar Mass • The mass (in grams) of one mole of a compound is called its molar mass.

23. Solving Problems What is the molar mass of one mole of CaCO3? • Looking for: • … molar mass of CaCO3 • Given • … chemical formula • Relationships: • no. amu in formula = molar mass in grams

24. Solving Problems • Solution • Use periodic table and round values as needed. Formula mass CaC03 = 100.19 g 1 mole CaC03 = 100.19 g CaCO3

26. 17.2 Chemical Equations • When a chemical reaction is written using chemical formulas and symbols, it is called a chemical equation.

27. 17.2 Chemical equations • An arrow is always included between reactants and products. • It means “to produce” or “to yield.” to produce Reactants Products “Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”

28. 17.2 Numbers in equations

29. 17.2 Balancing equations • The law conservation of mass is applied by balancing the number and type of atoms on either side of the equation.

30. 17.2 Balancing equations • Counting atoms is necessary to balance an equation. How many carbon atoms? How many hydrogen atoms? How many oxygen atoms?

31. 17.2 Balancing chemical equations • A balanced chemical equation has the same number of each type of atom on the product side and the reactant side. • To balance the equation, we add another water molecule to the product side and add another oxygen molecule to the reactant side. • We can practice balancing equations using CPO periodic table tiles and pencil and paper.

32. 17.2 Steps for balancing • If not provided, write the word form of the equation. • Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and water.

33. 17.2 Steps for balancing • If not provided, write the chemical equation from the word form.

34. 17.2 Steps for balancing • Count the number of each type of atom on both sides.

35. 17.2 Steps for balancing • Add coefficients to balance the equation.

37. Solving Problems • In this reaction, chalcocite (a mineral) reacts with oxygen in the presence of heat. The products are a type of copper oxide and sulfur dioxide. Balance this equation: Cu2S + O2 → Cu2O + SO2

38. Solving Problems • Looking for: • …the coefficients for each molecule • Given • … chemical formulas which show types and no. of atoms

39. Solving Problems • Relationships • Coefficients can be added in front of any chemical formula in a chemical equation. • When a coefficient is added in front of a chemical formula, all atoms in that formula are multiplied by that number. • Use common denominators to help choose coefficients to try.

40. Solving Problems • Solution- Trial and error

41. Chapter Seventeen: Chemical Change • 17.1 Chemical Reactions • 17.2 Balancing Equations • 17.3 Classifying Reactions

42. Chapter 17.3 Learning Goals • Classify reactions based on how atoms combine to create new substances. • Discuss applications of polymer science. • Study examples of combustion reactions.

43. Key Question: How can you predict the products of a chemical reaction? Investigation 17C Classifying Chemical Reactions

44. 17.3 Addition reactions • The process of creating large molecules from small ones is called polymerization.

45. 17.3 Addition reactions • In an addition reaction, two or more substances combine to form a new compound.

46. 17.3 Addition reaction A+B----->AB Fe (s)+O2 (g)----->Fe2O3(s) Remember to balance! Fe+O2----->Fe2O3 4 3 2

47. 17.3 Decomposition reactions • A chemical reaction in which a single compound is broken down to produce two or more smaller compounds is called a decomposition reaction.

48. 17.3 Decomposition reaction AB-energy-> A+B 2 H2O (l) -electricity-> 2 H2(g) + O2 (g) Na2O(s) 2 NaHCO3(s) + CO2 (g) + 2 H2 (g) -heat->

50. 17.3 Single Displacement • In a single-displacement reaction, one element replaces a similar element in a compound.