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Chapter 5: Chemical Reactions

Chapter 5: Chemical Reactions. Suggested Problems: 1-8, 20, 28, 30, 35, 44, 46, 50, 52, 56. Reactants Products. Chemical Equations. Reactants: Are the species that are combined together to give a chemical change

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Chapter 5: Chemical Reactions

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  1. Chapter 5: Chemical Reactions Suggested Problems: 1-8, 20, 28, 30, 35, 44, 46, 50, 52, 56

  2. Reactants Products Chemical Equations • Reactants: Are the species that are combined together to give a chemical change • Products: Are the species that are created as a result of the chemical change

  3. A + B C + D Chemical Equations • A and B are reactants • C and D are products • Equation is read as: • A reacts with B to yield ( or give) products C and D • Think of the arrow as an algebraic equals sign • The equation is balanced when the atoms on the right equal the atoms on the left

  4. Balancing Equations Basic Rules • Balance elements other than oxygen and hydrogen first • Balance polyatomic ions as units if on both sides of the equation • Balance oxygen and hydrogen last • Never add subscripts add COEFFICIENTS

  5. Mg(OH)2 + HCl MgCl2 + H2O Mg(OH)2 + 2HCl MgCl2 + 2H2O Mg(OH)2 + 2HCl MgCl2 + H2O Balancing Equations: Atom Inventory 1 1 1 Mg O H Cl Mg O H Cl 1 2 2 1 2 3 4 2 4 2 2 1 2

  6. Fe2(SO4)3 + BaCl2 Ba(SO4) + FeCl3 Balance the Following Equation

  7. Types of Chemical Reactions • Redox • Decomposition • Combination • Replacement • Single and Double • Combustion • Acid Base

  8. Helpful Phrases for REDOX Reactions • Reduction: Gain of electrons by a species • Oxidation: Loss of electrons by a species LEO the lion says GER! OILRIG GER!

  9. Helpful Phrases for REDOX Reactions • Oxidizing Agent: This is the species that is reduced in a chemical reaction • Reducing Agent: This is the species that is oxidized in a chemical reaction • Reduction can’t happen without an oxidation to provide the electrons

  10. Helpful Phrases for REDOX Reactions • Oxidation Number (ON): This is the charge of a species in a chemical formula Rules • The ON in uncombined elements is zero • The ON of simple ions equals its charge • The ON of group 1A and 2A elements equals +1 and +2 respectively • The ON of H is +1 • The ON of O is -2 except in peroxide it is -1 • The sum of the ON’s of a chemical formula is zero • The sum of the ON’s of a polyatomic ion equal the charge of the polyatomic ion

  11. REDOX Reactions • Simply boils down to a change in oxidation numbers of the products and reactants • REDOX reaction is a broad classification that contains: • Combustion reactions • Decomposition reactions • Combination reactions • Single Replacements reactions

  12. KI + Cl2 KCl + I2 REDOX Example • Balance the following equation. Then identify the ON’s of each species in the above reaction as well as identify the oxidizing agent and reducing agent.

  13. A B + C Decomposition Reactions • A reaction in which one species is broken down into 2 or more simpler substances

  14. A + B C Combination Reactions • Known also as addition or synthesis reactions: 2 or more substances react to form a single substance

  15. A + BX B + AX Single Replacement • Is a reaction in which one element reacts with a compound and replaces another element

  16. AY + BX BY + AX Double Replacement • A reaction in which the cations of two compound switch anion partners

  17. C6H12O6 + O2 CO2 + H2O Combustion Reactions • An organic compound is heated in the presence of oxygen gas, resulting in the products of H2O and CO2 • Balance this equation!

  18. Endothermic and Exothermic Reactions • Endothermic Reaction: is a reaction that requires energy as a reactant • Exothermic Reaction: is a reaction that releases energy as a product • Energy is most often in the form of heat • So it is common to think of endothermic reaction as being cold and an exothermic reaction as being hot

  19. Mg(OH)2 + 2HCl MgCl2 + 2H2O Stoichiometry and Chemical Reactions • The coefficients used to balance chemical reactions can now be used as conversion factors!!!

  20. Mg(OH)2 + 2HCl MgCl2 + 2H2O Stoichiometry Example • If 25 ml of HCl, with a density of 1.079 g/mL reacts with Mg(OH)2, how many grams of water is produced?

  21. Limiting Reagent

  22. Limiting Reagent • Reaction mixtures do not always consists of the perfect stoichiometric ratio of reactants • Frequently on or more reagents are in excess; the other is called the limiting reactant (or limiting reagent) • The limiting reagent is present in the smallest stoichiometric amount, but not necessarily the smallest molar amount

  23. Limiting Reagent: Example • Aluminum reacts with bromine to give aluminum bromide • If 3.40 grams of Al are mixed with 26.2 grams of Br2, which is the limiting reagent?

  24. Theoretical Yield • Theoretical Yield is the maximum possible amount of product that can be produced • The theoretical yield is determined by the limiting reagent

  25. Theoretical Yield Example • What mass of aluminum bromide can be produced from 3.40 grams of Al and 26.2 grams of Br2?

  26. Percent Yield • The percent yield:

  27. Percent Yield: Example • If 12.5 grams of AlBr3 are isolated from the reaction of 3.40 grams of Al and 26.2 grams of Br2, what is the percent yield?

  28. Guideline for the Rest of the YEAR Units of A given Moles of A Moles of B Units of B wanted

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