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  1. Chemical Reactions Chapter 14 Material on Midterm

  2. A model formula • Chemicals react in very precise ways. In this activity, you will model a chemical reaction and will predict how chemicals react.

  3. Section 1: Forming New Substances • Objectives: • Give examples and explain of how chemical reactions produce new substances that have different chemical and physical properties • Identify four signs that indicate that a chemical reaction might be taking place • Explain what happens to chemical bonds during a chemical reaction

  4. Section 1: Forming New Substances • Chemical Reactions • A chemical reaction is a process in which one or more substances change to make one or more new substances. • Properties of starting materials (reactants) differ from ending materials (products) 4 Fe + 3 O2 2 Fe2O3

  5. Section 1: Forming New Substances • Signs of Chemical Reactions • Gas formation • Solid formation • The precipitate is the solid that is produced as a result of a chemical reaction in solution • Energy Change • Color Change

  6. Section 1: Forming New Substances • A Change of Properties • A sign of a chemical reaction does not GUARANTEE a chemical reaction • Boiling water produces bubbles, but it’s physical • KEY POINT: look for the formation of new products that have different properties

  7. Section 1: Forming New Substances • Bonds: Holding Molecules Together • To make a molecule… • The old bonds need to break • The new bonds need to form

  8. Section 1: Forming New Substances • New Bonds, New Substances • What happens with H2 + Cl2? • Hydrogen gas—flammable, colorless gas • Chlorine gas—greenish-yellow color; toxic • H-H bonds and Cl-Cl bonds break • H-Cl bonds form • Hydrogen chloride gas is nonflammable and colorless • NEW SUBSTANCE

  9. Section 1: Forming New Substances • New Bonds, New Substances • What happens with Na + Cl2? • Sodium—silver metal that reacts violently with water • Chlorine—green yellow gas that is poisonous • Na bonds and Cl-Cl bonds break • Na+ -- Cl- bonds form • Sodium chloride—harmless ionic compound that is white and dissolves in water • NEW SUBSTANCE

  10. Section 1: Forming New Substances • Section Review • Please answer the objectives on your objective summary sheet • Give examples and explain how chemical reactions produce new substances that have different chemical and physical properties • Identify four signs that indicate that a chemical reaction might be taking place • Explain what happens to chemical bonds during a chemical reaction

  11. Section 2: Chemical Formulas and Equations • Objectives: • Explain how to interpret and write simple chemical formulas • Explain how to and be able to write and balance simple chemical equations • Explain how a balanced equation shows the law of conservation of mass

  12. Section 2: Chemical Formulas and Equations • How many words can you make using the letters in the word “ m i d t e r m“ ? die diet dim dime dimer dimmer dire dirt edit id ire ired it item me merit met mid mime mimed mimermire mired mite miter red rid ride rim rimmed rite ted term tide tie tied tier time timed timer tire tired tried trim

  13. Section 2: Chemical Formulas and Equations • Chemical Formulas • All substance are formed from 94 naturally-occurring elements • Each has its own symbol • They combine in many ways! • Show the combinations with a chemical formula • A chemical formula is a shorthand ay to use chemical symbols and numbers to represent a substance

  14. Section 2: Chemical Formulas and Equations • Chemical formulas • A chemical formula shows how many atoms of each kind are present in a molecule • You will use element symbols and subscripts • Symbol: which element • Subscript : how many of each If there is a number in front, it is called a COEFFICIENT!

  15. Section 2: Chemical Formulas and Equations

  16. Section 2: Chemical Formulas and Equations

  17. Section 2: Chemical Formulas and Equations The Trick to figuring out how many is… CRISS CROSS APPLESAUCE!

  18. Section 2: Chemical Formulas and Equations • Criss…cross…applesauce? Mg2+ + Cl- Mg Cl MgCl2

  19. Section 2: Chemical Formulas and Equations • Chemical Equations • Universal

  20. Section 2: Chemical Formulas and Equations • Describing Reactions by Using Equations • A chemical equationuses chemical symbols and formulas as a shortcut to describe a chemical reaction. • Short • Understood by anyone

  21. Section 2: Chemical Formulas and Equations • From Reactants to Products • Reactants—left side • Reactants are substances or molecules that participate in a chemical reaction • Starting materials • Products—right side • Products are substances that form in a chemical reaction • Ending materials

  22. Section 2: Chemical Formulas and Equations • The Importance of Accuracy

  23. Section 2: Chemical Formulas and Equations • Why balance Equations • Alchemy is dead! • Atoms are never lost or gained in a chemical reaction • Lavoisier’s law of conservation of mass states that mass cannot be created or destroyed in ordinary physical and chemical equations

  24. Section 2: Chemical Formulas and Equations • What does this law mean to you? • When writing a chemical equation, the number of each type of element on the left side has to equal the number of each type of element on the right side 1) H2 + O2 H2O 2) 2 H2+ O2 2H2O

  25. Section 2: Chemical Formulas and Equations • How to Balance an Equation • You will need coefficients • The number in front of the element, molecule, or compound • This get distributed to the entire term • EX: 2CO2 2 carbon and 4 oxygen • NEVER change the subscripts—this would change the identity of the element, molecule, or compound!

  26. Section 2: Chemical Formulas and Equations • Section Review • Please answer the objectives on your objective summary sheet • Explain how to interpret and write simple chemical formulas • Explain how to and be able to write and balance simple chemical equations • Explain how a balanced equation shows the law of conservation of mass

  27. Section 3: Types of Chemical Reactions • Objectives: • List and describe the four types of chemical reactions • Explain how to classify a chemical equation as one of the four types of chemical reactions

  28. Section 3: Types of Chemical Reactions • Types of Chemical Reactions • There are four major types of chemical reactions • Synthesis reaction • Decomposition reaction • Single-displacement reaction • Double-displacement reaction

  29. Section 3: Types of Chemical Reactions • Synthesis Reactions • A synthesis reaction is a reaction in which two or more substances combine to form one new compound • General formula: A + B  AB Synthesis means TO MAKE

  30. Section 3: Types of Chemical Reactions • Decomposition Reactions • A decomposition reaction is a reaction in which a single compound breaks down to form two or more simpler substances • General formula: AB  A + B Decomposing is BREAKING DOWN

  31. Section 3: Types of Chemical Reactions • Single-Displacement Reactions • A single-displacement reaction is a reaction in which one element or radical takes the place of another element or radical in a compound • General formula: A + BC  AC + B Single means ONE and displacement means to MOVE OUT OF THE WAY

  32. Section 3: Types of Chemical Reactions • Double-Displacement Reactions • A double-displacement reaction is a reaction in which ions from two compounds exchange places • General formula: AB + CD  AD + BC Double means TWO and displacement means GET OUT OF THE WAY

  33. Section 3: Types of Chemical Reactions • Reactivity and the single-and double-displacement reaction • Elements/compounds have to be more reactive to “bump out” another element or compound • Elements in Group 1—most reactive metals • Elements in Group 17—most reactive nonmetals

  34. Section 3: Types of Chemical Reactions • Section Review • Please answer the objectives on your objective summary sheet • List and describe the four types of chemical reactions • Explain how to classify a chemical equation as one of the four types of chemical reactions

  35. Section 4: Energy and Rates of Chemical Reactions • Objectives: • Compare exothermic and endothermic reactions • Explain activation energy • Interpret an energy diagram • Describe the five factors that affect the rate of a reaction

  36. Section 4: Energy and Rates of Chemical Reactions • Reactions and Energy • Two main types of reactions • Exothermic reactions • Endothermic reactions

  37. Section 4: Energy and Rates of Chemical Reactions • What is an exothermic reaction? • An exothermic reaction is a chemical reaction in which heat is released to the surroundings • Energy is usually listed as a product 2 Na Cl2 2 NaCl + energy

  38. Section 4: Energy and Rates of Chemical Reactions • What is an endothermic reaction? • An endothermic reaction is a chemical reaction in which energy is taken in • Energy is usually listed as a reactant 2 H2O + energy 2 H2 + O2 6CO2+ 6 H2O + energy C 6H12O6 + 6 O2

  39. Section 4: Energy and Rates of Chemical Reactions • The Law of Conservation of Energy • Similar to the law of conservation of mass • The law of conservation of energy states that energy cannot be created or destroyed • Instead, energy changes forms and transfers • Stored in chemical bonds

  40. Section 4: Energy and Rates of Chemical Reactions • Rates of Reactions • You need energy to make anything happen

  41. Section 4: Energy and Rates of Chemical Reactions • Activation Energy • Activation energy is the smallest amount of energy required to start a chemical reaction • Sources of Activation Energy • Friction • Electric spark • Light • Heat

  42. Section 4: Energy and Rates of Chemical Reactions • How do I read an energy diagram? • X axis—time • Y axis—energy • Curved line—amount of energy throughout reaction • Straight line at beginning—reactants • Straight line at end—products • Curve from reactants from peak—activation energy • Difference between reactants and products—energy differ • ENDOTHERMIC: R < P (less energy in reactants) • EXOTHERMIC: R > P (more energy in reactants)

  43. Section 4: Energy and Rates of Chemical Reactions • Factors Affecting Rates of Reactions • Temperature • Concentration • Surface Area • Inhibitors • Catalysts