Chemical Reactions. Chemical Reaction occur when atoms collide. Reaction rates change from increasing or decreasing collisions

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1 Chemical Reactions

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3 Questions 1. What is a chemical reaction 2. What evidence suggests that a chemical reaction has taken place? 3. What factors can affect the rate of a chemical reaction (how fast the reaction occurs) 4. Compare reactants and products in a chemical reaction 5. What does it mean to have a balanced reaction 6. Compare endothermic and exothermic reactions 7. Compare synthesis and decomposition reactions 8. What is a combustion reaction 9. What is a replacement reaction

4 Chemical Reactions Chemical Reaction Chemical bonds are formed or broken Physical changes are not chemical reactions Evidence of chemical reactions 1. Energy is released 2. Bubbles form 3. Color Change 4. Precipitate forms 5. Change is difficult to reverse

5 Chemical Reactions Chemical Reaction occur when atoms collide Reaction rates change from increasing or decreasing collisions Ways of changing reaction rate: 1. Nature of reactants 2. Concentration 3. Pressure 5. Catalysts 6. Agitation 7. Surface Area 4. Temperature

6 Chemical Equations Equation Description of the chemical reaction Reactants Ingredients or substance before reaction Reactants go on left side of equation Products Substance after the reaction Products go on right side of equation Equations are balanced so you have the same number of atoms on both sides of the equation

7 Chemical Equations Examples A + B AB A 2 + 2B 2 2AB 2 4H + O 2 2H 2 O 2H 2 O 2H + O2

8 Two Important Chemical Reactions Sunlight 6 CO H 2 O C 6 H 12 O 6 + 6O 2 Chlorophyll C 6 H 12 O 6 + 6O 2 6 CO H 2 O

9 Chemical Reactions Reaction Reactant Product Other Photosynthesis Cellular Respiration

10 I Bleed Mountain Dew One important chemical reaction inside of your body involves CO 2. Your cells are constantly producing CO 2 as a by-product of cellular respiration. This CO 2 is carried to your lungs by your bloodstream and then released when you exhale. However, CO 2 is not very soluble in water and your body could never get rid of it fast enough if not for a chemical reaction.

11 I Bleed Mountain Dew 2 This reaction converts CO 2 and water to carbonic acid, which is very soluble in water. In the lungs the reaction is then reversed and the CO 2 is able to be expelled. Carbonic acid is the same stuff that makes soda bubbly. Compare the ph of water and soda water. What can you infer about the effects of dissolving carbonic acid (or carbon dioxide for that matter) in water?

12 Review Questions Identify the reactants and the products in the following reactions: Hydrogen gas + Oxygen gas makes water Sugar ferments to ethyl alcohol and carbon dioxide Alcohol + oxygen becomes vinegar and water Burning methane releases carbon dioxide & water

13 Energy and Chemical Reactions Use the temperature probe to record the temperature of the following chemical reactions. Make sure the temperature probe is ready to use before you mix the reactants. 5 g of baking soda (NaHCO 3 ) + 10-ml Vinegar (CH 3 COOH) 5 g of dry yeast + 10ml hydrogen peroxide (H 2 O 2 )

14 Energy & Chemical Reactions Endothermic Exothermic Requires energy Reactants have less energy than products Few reactions Energy Breaking bonds requires energy Activation energy is part of the reaction Releases energy Products have less energy than reactants Majority of reactions

15 Review Are the following reactions exothermic or endothermic A + B + Energy AB AB A + B + Energy H 2 O + Energy 2H 2 + O 2 2H 2 + O2 H 2 O + Energy

16 Types of Chemical Reactions Synthesis Reactions Combination Exothermic Reaction Reactants simple Products complex Analogy: Skinny Bird + Fat Worm Fat Bird i.e. 2H 2 + O 2 2H 2 O Decomposition Reactions Separation Endothermic Reaction Reactants complex Products simple Analogy: Egg Egg Shell + Turtle i.e. 2H 2 O 2H 2 + O 2

17 Types of Chemical Reactions Replacement Reactions One or more elements trade places with each other Exothermic or Endothermic Analogy: Unfaithful wife or husband Ross & Sam Ruschman + Leah Rinker Ross & Leah Ruschman + Sam Beebe i.e. Cl + NaBr Br + NaCl Combustion Reactions Synthesis Reaction Reactant: O 2 and some compound Product: H 2 O and CO 2 i.e. Burning wood uses wood and oxygen and produces water vapor & carbon dioxide while releasing heat

18 General Misconceptions T/F The rate of reactions is increased by rapid stirring T/F Atoms can reproduce T/F Elements can form other elements

19 Review Identify the following reactions as synthesis, decomposition, replacement, or combustion A + B C A + BC AB + C 2Ag + S Ag 2 S C 6 + O 12 6CO 2 Cl 2 + 2NaBr Br 2 + 2NaCl CH 4 + 2O 2 CO 2 + 2H 2 O