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Chemical Equations & Reactions

Chemical Equations & Reactions. Describing a Chemical Reaction. Indications of a Chemical Reaction Evolution of heat, light, and/or sound Production of a gas Formation of a precipitate Color change. 4 Al(s) + 3 O 2 (g) 2 Al 2 O 3 (s). Chemical Equations.

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Chemical Equations & Reactions

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  1. Chemical Equations & Reactions

  2. Describing a Chemical Reaction Indications of a Chemical Reaction • Evolution of heat, light, and/or sound • Production of a gas • Formation of a precipitate • Color change

  3. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. The numbers in the front are called stoichiometric coefficients. The letters (s), (g), and (l) are the physical states of compounds.

  4. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations This equation means: 4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 or 4 Al moles + 3 O2moles yield 2 moles of Al2O3

  5. Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (reactants), the amount of matter in a system does not change. The Law of Conservation of Matter Kotz web

  6. Chemical Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

  7. Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse

  8. Characteristics of Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.

  9. Chemical Equations • Reactants – the substances that exist before a chemical change (or reaction) takes place. • Products – the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

  10. Word Equations • A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactant Product

  11. Unbalanced and Balanced Equations H Cl Cl H H Cl H Cl Cl Cl H Cl H H H2 + Cl2 2 HCl (balanced) H2 + Cl2 HCl (unbalanced) reactants products reactants products H H 2 1 2 2 Cl Cl 2 1 2 2

  12. Meaning of Chemical Formula Chemical Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

  13. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

  14. Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.

  15. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide  bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl2 + NaBr  Br2 + NaCl 3) Determine the coefficients that make the equation balance. Cl2 + 2 NaBr  Br2 + 2 NaCl

  16. Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al2(SO4)3 + CaCl2 CaSO4 + AlCl3 3) Determine the coefficients that make the equation balance. Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3

  17. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

  18. Reactants  Products Unbalanced

  19. Showing Phases in Chemical Equations • Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) • Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) • Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g) H2O(s) H2O(l) H2O(g)

  20. Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

  21. Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction D 2 atm pressure 0 oC MnO2

  22. Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + BC  AC + B BDouble-replacement reaction AB + CD  AD + CB HX + BOH  BX + HOH Neutralization reaction CH + O2 CO2 + H2O Combustion reaction (of a hydrocarbon) Ause activity series to predict Bdriving force…water, gas, or precipitate

  23. Chemical Equations

  24. Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2 2 NaCl Na Cl Na+ Cl - Cl Cl - Na+ Na General form: A + B  AB element or element or compound compound compound

  25. Na Cl Cl Na Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2 2 NaCl Na Cl  Cl Na General form: A + B  AB element or element or compound compound compound

  26. Formation of a solid: AgCl AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)

  27. H H H H Decomposition Reaction Decomposition reaction 2 H2O + 2 H2 O2 H O O H + H O O H General form: AB A + B compound two or more elements or compounds

  28. Single and Double Replacement Reactions Single-replacement reaction Mg + CuSO4 MgSO4 + Cu General form: A + BC  AC + B Double-replacement reaction CaCO3 + 2 HCl  CaCl2 + H2CO3 General form: AB + CD  AD + CB

  29. Ca Activity Series Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Foiled again – Aluminum loses to Calcium Halogen Reactivity F2 Cl2 Br2 I2

  30. Potassium reacts with Water P O W !

  31. Double Replacement Reaction K2CO3 (aq) Potassium carbonate + BaCl2 (aq) Barium chloride 2 KCl (aq) Potassium chloride + BaCO3 (s) Barium carbonate

  32. Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustion Reactions

  33. Summary of Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustion Reactions Synthesis reactions (Reactants are elements.) Decomposition reactions (Products are elements.)

  34. Summary of Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustion Reactions Synthesis reactions Decomposition reactions

  35. IONIC BONDING: Formation of Magnesium Chloride Cl Cl Mg Mg2+ Cl Cl Loses 2e- Each gains 1e- One magnesium ion Two chloride ions Mg2+ Cl1- [(2+) 2 (1-) = 0] MgCl2 magnesium chloride

  36. IONIC BONDING: Formation of Magnesium Chloride Cl Cl Mg2+ Mg Mg2+ Cl Cl Loses 2e- Each gains 1e- One magnesium ion Two chloride ions Mg2+ Cl1- [(2+) 2 (1-) = 0] MgCl2 magnesium chloride

  37. Production of Methanol

  38. A Mixture of Molecules

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