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To learn the signals that show a chemical reaction has occurred

Objectives. To learn the signals that show a chemical reaction has occurred To learn to identify the characteristics of a chemical reaction To learn the information given by a chemical equation To learn various classification schemes for reactions.

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To learn the signals that show a chemical reaction has occurred

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  1. Objectives • To learn the signals that show a chemical reaction has occurred • To learn to identify the characteristics of a chemical reaction • To learn the information given by a chemical equation • To learn various classification schemes for reactions

  2. SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions. • b. Experimentally determine indicators of a chemical reaction specifically precipitation, gas evolution, water production, and changes in energy to the system. - How are types of chemical reactions determined?

  3. Chemical reactions involve a rearrangement of the ways atoms are grouped together. • A chemical equation represents a chemical reaction. • Reactants are shown to the left of an arrow. • Products are shown to the right of the arrow.

  4. In a chemical reaction atoms are not created or destroyed. • Law of Conservation of Mass • All atoms present in the reactants must be accounted for in the products. • Same number of each type atom on both sides of arrow

  5. Physical states of compounds are often given in a chemical equation.

  6. A. Ways to Classify Reactions • Driving forces for a reaction: • Formation of a solid • AB + CD  AD + CB • Precipitation reaction • Double displacement reaction • Formation of water • H+(aq) + OH−(aq) H2O(l) • Acid-base reaction

  7. A. Reactions That Form Water: Acids and Bases • Arrhenius Acids and Bases • A strong acid is one in which virtually every molecule dissociates (ionizes) in water to an H+ ion and an anion.

  8. A. Reactions That Form Water: Acids and Bases • Arrhenius Acids and Bases • A strong base is a metal hydroxide that is completely soluble in water, giving separate OH ions and cations. • Most common  NaOH, KOH

  9. A. Reactions That Form Water: Acids and Bases • Arrhenius Acids and Bases • The products of the reaction of a strong acid and a strong base are water and a salt. • Salt  Ionic compound • Net ionic equation • H+(aq) + OH−(aq) H2O(l) • Reaction of H+ and OH− is called an acid-base reaction. • H+ acidic ion • OH− basic ion

  10. A. Ways to Classify Reactions • Driving forces for a reaction: • Transfer of electrons (Oxidation-Reduction or Redox Reactions)

  11. A. Ways to Classify Reactions • Driving forces for a reaction: • Transfer of electrons • Formation of a Gas • A + BC  B + AC • Single replacement reaction

  12. B. Reactions of Metals with Nonmetals (Oxidation-Reduction) • Reactions between metals and nonmetals involve a transfer of electrons from the metal to the nonmetal. • oxidation – reduction reaction

  13. B. Other Ways to Classify Reactions • Combustion Reactions • Involve oxygen and produce energy so rapidly that a flame results • CH4(g) + 2O2(g) CO2(g) + 2H2O(g) • Special class of oxidation-reduction reactions

  14. B. Other Ways to Classify Reactions • Synthesis (Combination) Reactions • A synthesis reaction is one in which a compound forms from simpler materials. • C(s) + O2(g)  CO2(g) • Special class of oxidation-reduction reactions

  15. B. Other Ways to Classify Reactions • Decomposition Reactions • A decomposition reaction occurs when a compound is broken down into simpler substances. • 2H2O(l)  2H2(g) + O2(g)

  16. B. Other Ways to Classify Reactions • Summary

  17. Objectives • Write a balanced equation for a chemical reaction

  18. Balancing a Chemical Equation • Unbalanced equation • Balancing the equation • The balanced equation CH4 + 2O2 CO2 + 2H2O

  19. A chemical reaction is balanced by using a systematic approach: • Write the formulas of the reactants and products to give the unbalanced chemical equation. • Balance by trial and error starting with the most complicated molecule(s). • At the end check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides).

  20. Example:  • Hydrogen gas and oxygen gas combine to form liquid water. • Write the formulas of the reactants and products to give the unbalanced chemical equation. H2(g) + O2(g) H2O(l)

  21. Example:  • Hydrogen gas and oxygen gas combine to form liquid water. • Balance by trial and error starting with the most complicated molecule(s).

  22. Example:  • Hydrogen gas and oxygen gas combine to form liquid water. • At the end check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides). 2H2(g) + O2(g) 2H2O(l)

  23. Objectives • Identify factors that cause reactions to occur • Predict the solid that forms in a precipitation reaction • Write molecular, complete ionic, and net ionic equations

  24. A. Predicting Whether a Reaction Will Occur • Four driving forces favor chemical change. • Formation of a solid • Formation of water • Transfer of electrons • Formation of a gas

  25. B. Reactions in Which a Solid Forms • A reaction in which a solid forms is called a precipitation reaction. • Solid = precipitate

  26. B. Reactions in Which a Solid Forms • What Happens When an Ionic Compound Dissolves in Water? • The ions separate and move around independently.

  27. B. Reactions in Which a Solid Forms • What Happens When an Ionic Compound Dissolves in Water? • K2CrO4(aq) + Ba(NO3)2(aq) Products

  28. B. Reactions in Which a Solid Forms • How to Decide What Products Form • Determine the possible products from the ions in the reactants. • In our example • K2CrO4(aq) + Ba(NO3)2(aq) Products • The possible ion combinations are

  29. B. Reactions in Which a Solid Forms • How to Decide What Products Form • Decide which is most likely to be the yellow solid formed in the reaction. • K2CrO4(aq) reactant • Ba(NO3)2(aq) reactant • The possible combinations are KNO3 and BaCrO4. • KNO3 white solid • BaCrO4 yellow solid

  30. B. Reactions in Which a Solid Forms • Using Solubility Rules

  31. B. Reactions in Which a Solid Forms • Using Solubility Rules • Predicting Precipitates • Soluble solid • Insoluble solid • Slightly soluble solid

  32. B. Reactions in Which a Solid Forms

  33. C. Describing Reactions in Aqueous Solutions • Three types of equations: • Molecular (formula) equation  complete formulas of all reactants and products • Complete ionic equation  all strong electrolytes are shown as ions • Net ionic equation  only those components of the solution that undergo a change • Spectator ion (those that remain unchanged)  not shown in the net ionic equation

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