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Chapter 6 Chemical Reactions

Chapter 6 Chemical Reactions. Section 1 The Nature of Chemical Reactions (p. 184). Yields. Products Substance that is formed. Reactants Starting substance(s). I. Chemical reactions change substances – it rearranges atoms 25 O 2 (g) + 2 C 8 H 18 (l)  1 6 CO 2 (g) + 18 H 2 O(l).

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Chapter 6 Chemical Reactions

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  1. Chapter 6Chemical Reactions Section 1 The Nature of Chemical Reactions (p. 184)

  2. Yields Products Substance that is formed Reactants Starting substance(s) I. Chemical reactions change substances – it rearranges atoms 25 O2(g) + 2 C8H18(l)  16 CO2(g) + 18 H2O(l)

  3. Symbols used in chemical equations • aq – dissolved in water (aqueous) • s – solid • cr – crystalline solid • l – liquid • g - gas

  4. Section 1 The Nature of Chemical Reactions Chapter 6 Chemical Reaction

  5. Signs of a Chemical Reaction • Signs of a chemical reaction include: • production of gas • change of color • production of odor • giving off of heat/light • formation of a precipitate

  6. Section 1 The Nature of Chemical Reactions Chapter 6 Signs of a Chemical Reaction

  7. II. Energy and Reaction Activation Energy – energy that must be added to break bonds and start a reaction A. Energy is needed to break bonds (heat, electricity, sound, light, etc) B. Energy is sometimes released when new substances are formed (sometimes as heat or light)

  8. Law of conservation of energy • energy is not created or destroyed, it only changes form • amount of energy in reactants is same as amount in products • chemical energy • a type of energy found in chemical bonds. • Can be released or absorbed when chemical compound reacts to produce new substances.

  9. Section 1 The Nature of Chemical Reactions Chapter 6 Reaction Model

  10. 1. Exothermic – reaction where energy is released (sometimes felt as heat) - Products have less energy than reactants 2. Endothermic – reaction that absorbs energy - Products have more energy than reactants

  11. Section 2 – Reaction Types (p. 190)

  12. Section 2 – Reaction Types (p. 190) • Classifying types of reactions • A. Synthesis • 1. Two or more substances become one • 2. A + BAB • Example: In the following synthesis reaction, the metal sodium reacts with chlorine gas to form sodium chloride, or table salt. • 2Na + Cl2 → 2NaCl

  13. Section 2 Reaction Types Chapter 6 Synthesis Reaction

  14. B. Decomposition (Electrolysis is an example) 1. Complex substances are broken down into simpler ones 2. ABA + B • Example: The following shows the decomposition of water. • 2H2O → 2H2 + O2 • Electrolysis is the process in which an electric current is used to produce a chemical reaction, such as the decomposition of water.

  15. Section 2 Reaction Types Chapter 6 Decomposition Reaction

  16. Section 2 Reaction Types Chapter 6 Electrolysis

  17. C. Single Displacement (Replacement) 1. Changes one element for another – less reactive for a more reactive one 2. AX + BBX + A • Example: The single-displacement reaction between copper(II) chloride and aluminum is shown as follows. • 3CuCl2+ 2Al → 2AlCl3 + 3Cu

  18. D. Double Displacement (Replacement) 1. Exchange of two ions in two compounds 2. Shown by a formation of a gas, precipitate, or molecular compound 3. AX + BY AY + BX • Example: The double-displacement reaction that forms leadchromate is as follows. • Pb(NO3)2 + K2CrO4 → PbCrO4 + 2KNO3

  19. Section 2 Reaction Types Chapter 6 Double Displacement Reaction

  20. E. Combustion 1. Oxidation of an organic compound where heat is released 2. Oxygen is ALWAYS a reactant 3. Water is usually a product 4. Products depend on amount of oxygen

  21. Section 2 Reaction Types Chapter 6 Combustion Reaction

  22. F. Acid-Base Reaction(neutralization) 1. an acid and a base combine to produce a salt and water 2. HX + YOH HOH + YX • Example: The acid-base reaction that forms sodiumchlorideis as follows. • HCl + NaOH → H2O + NaCl

  23. Steps to Classify Reaction Types • Does it have H2O in products? Yes → go to step 2 No → go to step 3 • Does it have O2 in reactants? Yes → combustion No → acid-base rxn • Does it have a + on both sides? Yes → go to step 4 No → go to step 5 • Does it have 2 compounds in reactants & products? Yes → double displacement No → single displacement • Does it have a + in the reactants? Yes → synthesis No → decomposition

  24. Section 3 – Balancing Chemical Equations(p. 198)

  25. Section 3 – Balancing Chemical Equations Chapter 6 I. Describing Reactions A. chemical equation - representation of chemical reaction that uses symbols

  26. Section 3 Balancing Chemical Equations Chapter 6 Reading a Chemical Equation

  27. Section 3 Balancing Chemical Equations Chapter 6 Chemical Equation

  28. B. Balanced chemical equation - when the number of atoms of reactants matches the number of atoms of products. 1. follows law of conservation of mass (number of atoms in reactants = number of atoms in products) 2. cannot change formulas or subscripts 3. use coefficients to balance chemical equations

  29. Section 3 Balancing Chemical Equations Chapter 6 Law of Conservation of Mass

  30. Section 3 Balancing Chemical Equations Chapter 6 Balancing a Chemical Equation by Inspection

  31. C. Rules for Balancing Chemical Equations • Write the chemical equation with correct symbols and formulas • Count the number of atoms of each element on each side of the arrow • Balance using coefficients • Check your work by counting atoms again * NEVER CHANGE SUBSCRIPTS * to balance equation!!!

  32. II. Balanced Equations A. show conservation of mass B. can be used to determine ratios of reactants and products (called mole ratios) C. can be used to calculate amount of mass in reactants and in products.

  33. Calculating relative mass of compounds Step 1: use the periodic table to find atomic mass for each element Step 2 : add and multiply for each atom of each element to find the total mass of the reactants and the total mass of the products Step 3 : compare the total mass of the reactants to the total mass of the products (they should be equal) Law of Conservation of Mass states mass of reactants equals mass of products

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