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Chemical Reactions

Chemical Reactions . Objectives . Recognize Evidence of a chemical change. Represent chemical reactions with equations. Change word equations into formula equations. Given a description of a reaction, write a word and formula equation. Balance chemical equations.

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Chemical Reactions

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  1. Chemical Reactions

  2. Objectives • Recognize Evidence of a chemical change. • Represent chemical reactions with equations. • Change word equations into formula equations. • Given a description of a reaction, write a word and formula equation. • Balance chemical equations. • Translate a formula equation into a sentence. • Define and give a description of the major types of chemical reactions. • Classify reactions as one of five major types. • Predict the products of simple reactions when given the reactants. • Understand, explain, and apply the activity series of the elements.

  3. Skills • Memorize the diatomic elements • Memorize the symbols used in chemical equations. • Use the Activity Series for single replacement reactions • Use the Solubility Chart for Double Replacement Reactions • Know common gases • Memorize substances that decompose • Carbonic acid, H2CO3 • H2CO3(aq) H2O+ CO2(g) • Sulfurous acid, H2SO3 • H2SO3 (aq) H2O + SO2(g) • Ammonium hydroxide, NH4OH • NH4OH (aq) H2O + NH3(g)

  4. Chemical Reaction The process by which one or more substances are rearranged to form different substances is called a chemical reaction. Also called a chemical change Activity 1: Name Some Common Chemical Reactions

  5. Equations show • the reactants which enter into a reaction. • the products which are formed by the reaction. • the relative amounts of each substance used and each substance produced. • Reactants ® Products

  6. Two important principles to remember • Every chemical compound has a formula which cannot be altered. • A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.

  7. Evidence of a Chemical Reaction Activity #2 Indicators of a chemical reaction Procedure • Add 10.0 mL od distilled water to a small beaker. • Add 1 drop of .1 M NaOH to the water. • Add 15 drops of universal indicator to the water. Stir. • Record the color of the water. • Record the temperature of the water. • Drop an alka seltzer tablet into the water. • Observe the reaction. Record all observations including any temperature change. Analysis Questions Describe any color changes or temperature changes. Was a gas produced? How do you know? Did chemical change occur? Explain how you know. What is the purpose of the universal indicator? Make a list of five indicators of a chemical reaction.

  8. Evidence of a Chemical Reaction • Production of a Gas • Temperature Change • Color Change • Production of a Solid (precipitate) • Production of Water or other unionized substance

  9. Representing Reactions • We use chemical equations to represent reactions • Ways to show equations • Sentence Descriptions • Word Equations • Skeleton Equations • Balanced Chemical Equation

  10. Sentence Descriptions Every item is a word. • Copper reacts with chlorine to form copper (II) chloride • Iron (III) chloride is produced from iron metal reacting with chlorine gas

  11. Word Equations Words and symbols are used. • Copper + chlorine ® copper (II) chloride • iron(s) + chlorine(g)iron(III) chloride(s)

  12. Skeleton Equation Uses chemical formulas instead of words Fe (s) + Cl2 (g) FeCl3 (s)

  13. Balanced Chemical Equation 2Fe (s) + 3Cl2 (g) 2FeCl3 (s)

  14. Some things to remember about writing equations • The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2 • The sign,  →  , means "yields" and shows the direction of the action. • A small delta, ( ), above the arrow shows that heat has been added. • A double arrow,  ↔  , shows that the reaction is reversible and can go in both directions.

  15. Chemical Equation • In order to obey the Law of Conservation of Mass equations must be Balanced: • Coefficients:number written in front of a chemical formula to indicate the smallest number of particles involved in the reaction.

  16. Steps for Balancing • Write skeleton equation. • Change the coefficients to make the number of atoms of each element equal on both sides of the equation. NEVER CHANGE A SUBSCRIPT!!! • Write the coefficients in the smallest ratio possible. • Check your work.

  17. Helpful hints for balancing chemical equations • Start with “Big Formulas” C2H6O2 • Save single elements for last O2 or Cu • Balance hydrogens second to last • Balance oxygens last • Check for lowest ratio • Do not change your subscripts • Balance the polyatomic ions as one unit (if it didn’t break apart) • Perform a final check

  18. If your equation doesn’t balance, check your formulas!!

  19. Classifying Chemical Reactions • Five Types of Chemical Reactions • Synthesis Reaction • Decomposition Reaction • Single Replacement Reaction • Double replacement Reaction • Combustion Reaction: oxygen combines with a substance and produces heat and light

  20. Synthesis Reaction:one product is formed from more than one simpler substances • A + B  AB • Activity: Reaction of Iron with Oxygen Gas

  21. Decomposition Reaction:One substance is broken down into one or more simpler substances: usually by the addition of energy • AB  A + B • Activity: Elephant Toothpaste

  22. Decomposition of Hydrogen Peroxide

  23. Single Replacement Reaction:atoms of one element replace another element in a compound • A + BC  B + AC • Activity: Reaction of iron with copper (II) nitrate

  24. Reaction Notes

  25. Double Replacement Reaction Involves the exchange of ions between two compounds AB + CD  AD + CB Activity: Copper (II) chloride reacts with sodium hydroxide

  26. Reaction Notes

  27. Combustion Reaction • Oxygen combines with a substance and produces heat and light • Most likely: Hydrocarbon (CxHy) Combustion • CxHy + O2  H2O + CO2 • X + O2  X2O3 • Demo: Methane Snake

  28. Reaction Notes

  29. Classify Each Reaction • Ca + O2 CaO • Br + LiI  LiBr + I • Al + Fe(NO3)2 Al(NO3)3 + Fe • MgO + HCl  MgCl2 + H2O • C4H10 + O2 CO2 + H2O • NH4NO2 NH3 + H2O • (NH4)3PO4 + Sr(OH)2 Sr3(PO4)2 + NH4OH • H2SO4 + NaOH  Na2SO4 + H2O • Zn + AgNO3 Zn(NO3)2 + Ag • CuNO3 + KCl  KNO3 + CuCl

  30. Predicting Products • Given the reactants predict what is formed • Write formulas for reactants • Identify the type of reaction • Rearrange the atoms to write formulas for products.

  31. Single Replacement Reactions • Atoms of one element replace another element in a compound • A + BC  B + AC There are 3 Ways that a Single Replacement Reaction can occur.

  32. 1.) Metal replaces another metal in a compound • when zinc combines with iron (II) chloride the zinc replaces iron in the compound • Z n + FeCl2Fe + ZnCl2

  33. 2.) Metal replaces hydrogen in an acid or water

  34. 3.) Nonmetal (halogen) replaces another nonmetal(halogen)in a compound • Br2 + LiILiBr + I2

  35. Single Replacement Cartoon

  36. How can we tell if a single replacement reaction will happen? • Use the activity series of the elements • If the free element is more active than the element in the compound the reaction will happen • If the free element is below the element in the compound the reaction will not happen

  37. The Activity Series

  38. Another way to look at it • Bigger, stronger, orange shirted guy replaces white shirt guy in the dancing couple • Now we have new couple and new single guy

  39. Single Replacement Lab and Examples for you to Predict the Products Some Examples to Observe before lab http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/series/3perform.htm

  40. Double Replacement Reactions • two ionic compounds are mixed together in water • In water the ionic compounds split into anions and cations. • The cations have an opportunity to swap anions • A reaction occurs, if by swapping anions, a product is formed that cannot split apart into anions and cations AB + CD  AD + CB

  41. AgNO3(aq) + KCl(aq)AgCl(s) + KNO3(aq)

  42. Double Replacement: Will it occur? • A reaction occurs when a pair of ions comes together to produce a substance that removes ions from the solution. • one of the following must occur • a precipitate: a solid produced during a reaction • a gas • Water or other unionized substance • a product that decomposes • http://www.wisc-online.com/objects/ViewObject.aspx?ID=gch1404

  43. No Driving Force • What happens when one of the three possible products is not formed? • Nothing • All ions remain in solution (dissolved) NaNO3(aq) + KCl(aq)��NaCl(aq) + KNO3(aq)

  44. Without a driving force there is no change in the solution so we say No Reaction has taken place

  45. Reactions that form a PrecipitatePbCl2(aq) + KI(aq) PbI2(s)+ KCl(aq)Solubility Chart

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