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Understanding Chemical Reactions: Types, Balancing, and Examples

This chapter provides a comprehensive overview of chemical reactions, focusing on reactants and products, the concept of yielding, and balancing chemical equations to adhere to the law of conservation of matter. Key types of reactions discussed include combination, decomposition, single replacement, double replacement, and combustion reactions. Examples help illustrate each type, emphasizing the importance of coefficients and the rules for balancing equations. Additionally, the activity series is introduced, detailing how it influences the outcomes of single replacement reactions.

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Understanding Chemical Reactions: Types, Balancing, and Examples

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  1. Chapter 8 Chemical Reactions

  2. Reactants Products • + - separates reactants and products • - “yields” • - reversible reaction • (s) - solid • (l) - liquid • (g) - gas

  3. (aq) – aqueous solution, dissolves in H2O • - heat • Pt - catalyst

  4. Examples • Fe (s) + O2 (g) Fe2O3 (s) 4Fe (s) + 3O2 (g) 2Fe2O3 (s)

  5. Balancing Chemical Equations • Balanced equations obey the law of conservation of matter. • Balanced Equation – must have the same number of atoms of each element in both sides of the equation.

  6. Examples • C(s) + O2(g) CO2(g) 1 C + 2O 1C + 2O

  7. More Examples • 2C(s) + O2(g) 2CO 2C 2O 2C 2O

  8. Rules for Balancing Equations • 1) Determine the correct formulas for reactants and products • 2) Write the reaction • 3) Count the number of atoms of each element in the reactants and products (a poly-atomic ion appearing unchanged on both sides of the equation is counted as a single unit)

  9. Rules Cont’d • 4) Balance elements 1 at a time using coefficients • Coefficient: small whole # that appears in front of a formula in an equation • Balance O & H last • You cannot change subscripts

  10. Rules Cont’d • 5) Check to see if each atom is balanced • 6) Make sure Coefficients are lowest possible numbers

  11. Example • H2 + O2 H2O 2 1 2 4H2 + 2O2 4H2O

  12. Combination Reactions • Two or more substances react to form a single substance

  13. Formation of Binary Salts • M + X MX • Example • 2Na + Cl2 2NaCl

  14. Formation of Binary Oxides • M + O2 MO • Example • 2Zn + O 2 2ZnO

  15. Formation of Binary Acids • Examples • H2 + X HX • H2 + Cl2 2HCl

  16. Formation of Ternary Acids • Examples • H2O + nonmetallic oxide oxyacid • P2O5 + 3H2O 2H3PO4

  17. Formation of Bases • Examples • MO + H2O MOH • CaO + H2O Ca(OH)2

  18. Formation of Ternary Salts • Examples • MO + XOn MXOn+1 • CaO + CO2 CaCO3

  19. Decomposition Reactions • A single compound is broken down into 2 or more simpler products. • A B + C • CaCO3 CaO + CO2 • They can be a combination of elements and compounds

  20. Binary Compounds break down into constituent elements • Decomposition reactions require energy - (heat, light or electricity) • Example • 2H2O(l)electricity 2H2(g) + O2(g)

  21. Single Replacement Reactions • Atoms of an element replace the atoms of a second element in a compound • Gen Rxn: A + BC AC + B • Example • Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

  22. How do you know this will happen? • Whether one metal will replace another is determined by the relative activity of the 2 metals.

  23. Activity Series • Lists metals in order of decreasing reactivity • A positive metal will replace any metal found below it in the activity series • Metals from Li to Na replace H from acids and H20; Mg to Pb replace H from acids only.

  24. Double Replacement Rxns • Involve an exchange of positive ions between two compounds. • Generally take place in aqueous solutions

  25. For a double displacement rxn to occur one of the following must be true: • A precipitate forms • A gas forms and bubbles out of mixture • A molecular compound forms (ie H2O)

  26. Examples • AB + CD AD + CB AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

  27. Combustion Rxns • Oxygen reacts with another substance, producing energy in the form of heat or light. • Example • CxHy + O 2 CO2 + H2O

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