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8.2 Chemical Equations

8.2 Chemical Equations. law of conservation of mass reactants products diatomic molecule coefficient. Big Idea Ch8. In Chemical changes (reactions) atoms are rearranged, never made or destroyed Mass stays the same in chemical changes (reactions)

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8.2 Chemical Equations

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  1. 8.2 Chemical Equations law of conservation of mass reactants products diatomic molecule coefficient

  2. Big Idea Ch8 • In Chemical changes (reactions) atoms are rearranged, never made or destroyed • Mass stays the same in chemical changes (reactions) • Chemical reactions release energy or absorb energy to break and make chemical bonds

  3. 8.2 Chemical Equations Is matter conserved in chemical reactions? • Chemical equations show that in chemical reactions, atoms rearrange, but no atoms are gained or lost.

  4. 8.2 Chemical Equations Conservation of Mass • The law of conservation of mass The mass before a chemical reaction is equal to the mass after the reaction.

  5. 8.2 Chemical Equations Chemical Equation • Reactants react to produce Products • Reactants react to produce Products • Reactants react to produce Products • Reactants react to produce Products • Reactants react to produce Products

  6. Quick check Paper reacts with oxygen to produce carbon dioxide and ashes WHAT ARE THE REACTANTS? WHAT ARE THE PRODUCTS? Is the mass of the paper and oxygen the same as the carbon dioxide, water, and ashes?

  7. 8.2 Chemical Equations Balancing a Chemical Equation • Atoms are neither gained nor lost in a reaction, so both sides of the equation must have the same number of atoms. = Reactants Products

  8. 8.2 Chemical Equations Balancing Chemical Equations • “Tin + oxygen → tin oxide” reads as “tin plus oxygen produces tin oxide.” To save space let’s use the chemical symbols Sn + O2SnO2 PRODUCTS REACTANTS

  9. 8.2 Chemical Equations Balancing Equations • Use the symbols and formulas instead of words.

  10. 8.2 Chemical Equations Elements, Compounds, and Molecules (cont.)

  11. 8.2 Chemical Equations Elements, Compounds, and Molecules (cont.) • Some elements are diatomic, that is, they contain two atoms.

  12. 8.2 Chemical Equations Equations for Common Chemical Reactions Reaction of methane: CH4 + O2 → CO2 + H2O balance hydrogen CH4 + O2 → CO2 + 2H2O balance oxygen CH4 + 2O2 → CO2 + 2H2O

  13. 8.2 Chemical Equations Equations for Common Chemical Reactions (cont.) Baking soda and vinegar: NaHCO3 + HC2H3O2 → CO2 + H2O + NaC2H3O2

  14. 8.2 Chemical Equations Using Parentheses with Formulas • When counting atoms inside parentheses, the subscript multiplies all atoms inside. Ca + H2O → Ca(OH)2 + H2 Ca + 2H2O → Ca(OH)2 + H2

  15. 8.2 Chemical Equations Lesson 2 Review Which is a diatomic molecule? AO2 BH2O CCH4 D N

  16. 8.2 Chemical Equations Lesson 2 Review What is potassium bromide (KBr)? A an element B a mixture C a compound D a diatomic molecule

  17. 8.2 Chemical Equations Lesson 2 Review In the following equation, which is a reactant? Ca +2H2O → Ca(OH)2 + H2 A H2 B (OH)2 C Ca D none of the above

  18. End of Lesson 2

  19. 8.3 Energy and Chemical Change law of conservation of energy exothermic process endothermic process

  20. 8.3 Energy and Chemical Change Conservation of Energy • The law of conservation of energy states that energy cannot be created or destroyed, simply changed from one form to another.

  21. 8.3 Energy and Chemical Change • Where is the energy from sunlight?

  22. 8.3 Energy and Chemical Change Net Energy During a chemical reaction, reactant bonds are broken and product bonds are formed: • Breaking bonds releases energy. • Forming bonds absorbs energy. • The total of energy in and energy out makes the entire reactions release or absorb energy

  23. 8.3 Energy and Chemical Change Net Release of Energy (cont.) • An exothermic process releases energy. • The products in an exothermic reaction have less energy than the reactants.

  24. 8.3 Energy and Chemical Change Net Absorbtion of Energy (cont.) • An endothermic process absorbs energy. • The products in an endothermic reaction have a higher energy than the reactants.

  25. 8.3 Energy and Chemical Change Chemical Bonds • Molecules have chemical energy stored in their bonds. • Energy is stored in the food that you eat and transferred to your cells. • Where is the energy from sunlight? • Which is endothermic or exothermic?

  26. 8.3 Energy and Chemical Change Lesson 3 Review Products have a higher energy level than the reactants in an endothermic reaction. A False B True

  27. 8.3 Energy and Chemical Change Lesson 3 Review ____ bonds ____ energy. A Breaking; releases B Breaking; requires C Forming; requires D Ionic; release

  28. 8.3 Energy and Chemical Change Lesson 3 Review The law of ____ states that energy is neither created nor destroyed in a chemical reaction. A conservation of mass B definite proportions C conservation of matter D conservation of energy

  29. End of Lesson 3

  30. Chapter Resources Menu Chapter Assessment California Standards Practice Image Bank Science Online Click on a hyperlink to view the corresponding feature.

  31. Chapter Assessment 1 Which is a chemical change? A copper turning green from exposure to air B drying clothes C ice melting D none of the above

  32. Chapter Assessment 2 Which is a chemical property? Aboils at 100°C Bhas a volume of 500 ml C does not rust D has a luster

  33. Chapter Assessment 3 Which does NOT describe an exothermic reaction? AThere is a net release of energy. BThe reactants have a higher energy than the products . CThe reactants are lower in energy than the products. D The products are less stable than the reactants.

  34. Chapter Assessment 4 What is the coefficient of H2O? Ca + 2H2O → Ca(OH)2 + H2 A 1 B 0 C 4 D 2

  35. Chapter Assessment 5 How many (OH) molecules are in the products? Ca + 2H2O → Ca(OH)2 + H2 A 1 B 2 C 3 D 4

  36. SCI 5.b CA Standards Practice 1 In a chemical reaction, which law states the products have the same mass as the reactants? A Law of Conservation of Water B Law of Conservation of Energy C Law of Conservation of Mass D Law of Conservation of Particles

  37. CA Standards Practice 2 SCI 5.c Energy is ____ in exothermic reactions. A absorbed B created C released D stored

  38. CA Standards Practice 3 SCI 3.b If an equation is balanced, the number of atoms in the products is ____ the number of atoms in the reactants. A greater than B less than C equal to D none of the above

  39. CA Standards Practice 4 SCI X.X Which of the following is a physical change? A hydrogen burning B iron rusting C copper turning green when exposed to air D none of the above

  40. CA Standards Practice 5 SCI 3.f Symbols represent ____ and ____ represent molecules. A elements; formulas B formulas; equations C molecules; formulas D elements; equations

  41. Image Bank

  42. End of Resources

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