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Chemical Reactions

Chemical Reactions. Reactions and Equations Chapter 10, Section 1. Evidence of Chemical Reactions. Chemical Reaction: the process by which the atoms of one or more substances are rearranged to form different substances Break down food to produce energy Produce natural fibers, cotton and wool.

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Chemical Reactions

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  1. Chemical Reactions Reactions and Equations Chapter 10, Section 1

  2. Evidence of Chemical Reactions • Chemical Reaction: the process by which the atoms of one or more substances are rearranged to form different substances • Break down food to produce energy • Produce natural fibers, cotton and wool

  3. Representing Chemical Reactions • Reactants: the starting substances • Products: the substances formed during the reaction reactant 1 + reactant 2product 1 + product 2 Reactants written to the left of the arrow Products are written to the right of the arrow Arrow is read as “react to produce” or “yields”.

  4. Symbols Used in Equations

  5. Example • How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide?

  6. Example • How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide? First write the chemical formulas for the reactants to the left of the arrow including their physical states. C(s) + S(s)

  7. Example • How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide? Finally write the chemical formula for the product, liquid carbon disulfide to the right of the arrow, indicating its physical state. C(s) + S(s) CS2(l)

  8. Practice Problems • Write skeleton equations for the following word equations. • Hydrogen(g) + bromine(g) hydrogen bromide(g) • Carbon monoxide(g) + oxygen(g)  carbon dioxide(g) • Potassium chlorate(s)  potassium chloride(s) + oxygen(g)

  9. Balancing Chemical Equations • Chemical Equation: a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

  10. Steps for Balancing Equations 1. Write the skeleton equation for the reaction. ex. H2(g) + Cl2(g) HCl(g) 2. Count the atoms of the elements in the reactants. ex. H2  2 atoms of H Cl2  2 atoms of Cl 3. Count the atoms of the elements in the products. ex. HCl  1 atom H + 1 atom Cl 4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. Never change a subscript!! ex. H2(g) + Cl2(g)  2HCl(g)

  11. Steps for Balancing Equations 5. Write the coefficient in their lowest possible ratio. ex. (2:2)  (1:1) 6. Check your work.

  12. Example Problem • Write the balanced chemical equation for the reaction in which sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. The reaction occurs in water.

  13. Example Problem • Write the balanced chemical equation for the reaction in which sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. The reaction occurs in water. 2NaOH(aq) + CaBr2(aq) Ca(OH)2(s) + 2NaBr(aq)

  14. Practice Problems • Write chemical equations for each of the following reactions. • In water, iron(III) chloride reacts with sodium hydroxide, producing solid Iron (III) hydroxide and sodium chloride. • Liquid carbon disulfide reacts with oxygen gas, producing caron dioxide gas and sulfur dioxide gas. • Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfide.

  15. Chemical Reactions Classifying Chemical Reactions Chapter 10, Section 2

  16. Types of Chemical Reactions • Synthesis • Combustion • Decomposition • Single-replacement • Double-replacement

  17. Synthesis Reactions • A chemical reaction in which two or more substances react to produce a single product. • A + B  AB • Ex. 2Na + Cl2  2NaCl • Ex. CaO + H2O  Ca(OH)2 • Ex. 2SO2 + O2  2SO3

  18. Combustion Reactions • A reaction during which oxygen combines with a substance and releases energy in the form of heat and light. • Ex. 2H2 + O2  2H2O • Ex. C + O2  CO2 • Ex. CH4 + 2O2  CO2 + 2H2O

  19. Practice Problems • Write chemical equations for the following reactions. Classify each reaction into as many categories as possible. • The solids aluminum and sulfur react to produce aluminum sulfide • Water and dinitrogen pentoxide gas react to produce aqueous hydrogen nitrate. • The gases nitrogen dioxide and oxygen react to produce dinitrogen pentoxide gas. • Ethane gas (C2H6) burns in air, producing carbon dioxide gas and water vapor.

  20. Decomposition Reactions • A reaction in which a single compound breaks down into two or more elements or new compounds • Ex. AB  A + B • Ex. NH4NO3 N2O + 2H2O • Ex. 2NaN3  2Na + 3N2

  21. Practice Problems • Write chemical equations for the following decomposition reactions. • Aluminum oxide decomposes when electricity is passed through it. • Nickel (II) hydroxide decomposes to produce nickel (II) oxide and water. • Heating sodium hydrogen carbonate produces sodium carbonate, carbon dioxide and water.

  22. Replacement Reactions – Single & Double • Single-replacement reaction: A reaction in which the atoms of one element replace the atoms of another element in a compound. • Ex. A + BX  AX + B • Ex. Cu + 2AgNO3 2Ag + Cu(NO3)2

  23. Replacement Reactions • ** A metal will not always replace another metal • Reactivity determines whether or not a metal will replace another metal. • The most active metals, do not replace metals

  24. Example Problem • Predict the products that will result when these reactants combine and write a balanced chemical equation for each reaction. • Fe + CuSO4 • Br2 + MgCl2 • Mg + AlCl3

  25. Practice Problems • Predict if the following single-replacement reactions will occur. If a reaction occurs, write a balanced equation for the reaction. • 2K + ZnCl2 • Cl2 + 2HF • Fe + Na3PO4

  26. Double Replacement Reactions • A reaction involving the exchange of positive ions between two compounds dissolved in water most often producing a precipitate, water or a gas (H2S, HCN, and CO2) • Ex. AX + BY  AY + BX • Ex. Ca(OH)2 + 2HCl  CaCl2 + 2H2O • Ex. 2NaOH + CuCl2  2NaCl + Cu(OH)2

  27. Guidelines for Double-Replacement Reactions

  28. Practice Problems • Write the balanced chemical equations for the following double-replacement reactions. • Aqueous lithium iodide and aqueous silver nitrate react to produce solid silver iodide and aqueous lithium nitrate. • Aqueous barium chloride and aqueous potassium carbonate react to produce solid barium carbonate and aqueous potassium chloride. • Aqueous sodium oxalate and aqueous lead(II) nitrate react to produce solid lead(II) oxalate and aqueous sodium nitrate.

  29. Predicting Products of Chemical Reactions

  30. Chemical Reactions Reactions in Aqueous Solutions Chapter 10, Section 3

  31. Aqueous Solutions • Solutes: a substance dissolved in a solution • Solvent: the substance that dissolves a solute to form a solution • Aqueous solution: a solution in which the solvent is water

  32. Reactions that Form Precipitates 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s) In solution, these exist as ions. When their solutions are mixed, a precipitate of copper (II) hydroxide forms. Ionic equations are written to show the details of the reaction. 2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq)  2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)

  33. Reactions that From Precipitates • Complete ionic equation: an ionic equation that shows all of the particles in a solution as they realistically exist • Spectator ions: ions that do not participate in a reaction • Net ionic equations: ionic equations that include only the particles that participate in the reaction

  34. Example Problem • Write the chemical, complete ionic and net ionic equation for the reaction between aqueous solutions of barium nitrate and sodium carbonate that forms the precipitate barium carbonate.

  35. Practice Problems • Write chemical, complete ionic and net ionic equations for the following reactions that may produce precipitates. Use NR to indicate that no reaction occurs. • Aqueous solutions of potassium iodide and silver nitrate are mixed, forming the precipitate silver iodide. • Aqueous solutions of ammonium phosphate and sodium sulfate are mixed. No precipitate forms and no gas is produced. • Aqueous solutions of aluminum chloride and sodium hydroxide are mixed, forming the precipitate aluminum hydroxide. • Aqueous solutions of lithium sulfate and calcium nitrate are mixed, forming the precipitate calcium sulfate. • Aqueous solutions of sodium carbonate and manganese (V) chloride are mixed, forming the precipitate manganese (V) carbonate.

  36. Reactions That Form Water • Double replacement reaction • No evidence of chemical reaction is observable HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq) Complete Ionic Equation: H+(aq) + Br-(aq) + Na+(aq) + OH-(aq)  H2O(l) + Na+(aq) + Br-(aq)

  37. Reactions That Form Water Crossing out the spectator ions leaves us with: H+(aq) + OH-(aq) H2O(l) (net ionic equation)

  38. Example Problem • Write the chemical, complete ionic and net ionic equations for the reaction between hydrochloric acid and aqueous lithium hydroxide, which produces water.

  39. Practice Problems • Write chemical, complete ions and net ionic equations for the reactions between the following substances, which produce water. • Sulfuric acid and aqueous potassium hydroxide • Hydrochloric acid and aqueous calcium hydroxide • Nitric acid and aqueous ammonium hydroxide • Hydrosulfuric acid and aqueous calcium hydroxide • Phosphoric acid and aqueous magnesium hydroxide

  40. Reactions that Form Gases • Double Replacement Reaction • Commonly produce CO2, H2S and HCN 2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq) Ionic Equation 2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq)  H2S(g) + 2Li+(aq) + 2I-(aq)

  41. Example Problem • Write the chemical, complete ionic and net ionic equations for the reaction between hydrochloric acid and aqueous sodium sulfide which produces hydrogen sulfide gas.

  42. Practice Problems • Write chemical, complete ionic and net ionic equations for these reactions. • Perchloric acid reacts with aqueous potassium carbonate • Sulfuric acid reacts with aqueous sodium cyanide • Hydrobromic acid reacts with aqueous ammonium carbonate • Nitric acid reacts with aqueous potassium rubidium sulfide

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