1 / 83

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.

thai
Télécharger la présentation

Chemical Reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related