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Chemical Reactions: Understanding and Balancing Equations

Learn about chemical reactions, identification, and balancing equations. Explore types of reactions and stoichiometry calculations. Online resources and practice problems provided for further understanding.

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Chemical Reactions: Understanding and Balancing Equations

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  1. Chemical Reactions Intro to Reactions Ch 11 honors Ch 8 cp chem

  2. During your life you have witnessed numerous chemical reactions. What were some of those reactions? How did you know that a reaction was going on? How would you describe them to someone else?

  3. What do you see in this picture?

  4. A.Signs of a Chemical Reaction • Evolution of heat and light • Formation of a gas • Formation of a precipitate • Color change

  5. B.Law of Conservation of Mass • mass is neither created nor destroyed in a chemical reaction • total mass stays the same • atoms can only rearrange 4 H 2 O 4 H 2 O 36 g 4 g 32 g

  6. C. Chemical Equations A+B  C+D REACTANTS PRODUCTS

  7. C. Chemical Equations p. 246

  8. D. Writing Equations 2H2(g) + O2(g)  2H2O(g) • Identify the substances involved. • Use symbols to show: • How many? - coefficient • Of what? - chemical formula • In what state? - physical state • Remember the diatomic elements.

  9. D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. • How many? • Of what? • In what state?  3 2 Al (s) + 3 CuCl2 (aq) Cu (s) + 2 AlCl3 (aq)

  10. Describing Coefficients: individual atom = “atom” covalent substance = “molecule” ionic substance = “unit” E. Describing Equations 3CO2 2Mg  4MgO  3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide

  11. E. Describing Equations Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) to produce • How many? • Of what? • In what state? One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chloride and one molecule of hydrogen gas.

  12. Which of the following involves a chemical change? What evidence supports your choice? • The burning of gasoline • The freezing of water • Magnesium burning in oxygen to form magnesium oxide • Methane melting at -182C • Boiling of an egg • Liquid solutions of potassium chloride plus silver nitrate combining to form solid silver chloride • Nitroglycerine exploding on impact or when heated • Water boiling at 100C Not all the items are examples of a chemical change. What kind of change are they?

  13. Internet activity – introducing reactions • http://newtraditions.chem.wisc.edu/fpts/fbeqns/eqnintrf.htm • http://newtraditions.chem.wisc.edu/fpts/fbeqns/eqnintrf.htm

  14. End of day 1 notes Honors homework: Read section 11.1 • Do the reading strategy from page 321 • Page 329 #s 7,8, & 9 • Extra credit practice problems 1-6 CP Chem homework: read section 8-1

  15. 5. Chemical Reactions and Stoichiometry • Central Concepts: In a chemical reaction, one or more reactants are transformed into one or more new products. Chemical equations represent the reaction and must be balanced. The conservation of atoms in a chemical reaction leads to the ability to calculate the amount of products formed and reactants used (stoichiometry).

  16. 5.1 Balance chemical equations by applying the laws of conservation of mass and constant composition (definite proportions). 5.2 Classify chemical reactions as synthesis (combination), decomposition, single displacement (replacement), double displacement, and combustion. 5.3 Use the mole concept to determine number of particles and molar mass for elements and compounds. 5.4 Determine percent compositions, empirical formulas, and molecular formulas. 5.5 Calculate the mass-to-mass stoichiometry for a chemical reaction. 5.6 Calculate percent yield in a chemical reaction.

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