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Writing Simple Chemical Equations

Writing Simple Chemical Equations. Balancing and Classification of Reactions. Chemical Reactions. Balanced c hemical equations represent chemical reactions A substance which undergoes a chemical change has taken part in a chemical reaction

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Writing Simple Chemical Equations

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  1. Writing Simple Chemical Equations Balancing and Classification of Reactions

  2. Chemical Reactions • Balanced chemical equations represent chemical reactions • A substance which undergoes a chemical change has taken part in a chemical reaction • Remember the differences between chemical and physical change?

  3. Signs of a Chemical Reaction Indicators of a probable chemical reaction • These may be present in some physical changes too • Color Changes • Precipitation of a solid from a solution • Energy changes, heat or light absorbed or released • Odor Changes; like baked bread • Gas release- sometimes occurs in physical change too

  4. Mini-Lab 6.1 Energy Change Question: How can we observe energy changes? Background Information: • All chemical reactions involve an energy change. • Sometimes the change is so small that special detection instruments are needed to observe it. • Sometimes they can be observed easily. • Light, heat, sound, kinetic and potential are all forms of energy.

  5. Mini-Lab 6.1 Energy Change Procedure: • Place 25g of iron powder and 1g of NaCl in a reseal able bag • Add 30g of vermiculite to bag, seal bag and shake • Open bag and add 5ml of water, reseal and shake gently • Hold bag in your hands, note any changes you observe

  6. Mini-Lab 6.1 Energy Change Analysis: (answer the following in your notebook • Did you observe energy changes? If so, describe them • Did a chemical reaction take place? What kind of reaction? • Can you think of anytime in the real world, where this reaction might be useful? Explain

  7. Exothermic Reaction The Reaction has as one of the products, energy, in the form of heat!

  8. Endothermic Reactions These reactions use energy from the surroundings, in the form of heat, as one of the reactants; creating a cold product!

  9. Chemical Equations • Describe all changes that take place • Identify the substances that react • Called Reactants • Identify the substances formed • Called Products • Reactants: Iron and Oxygen • Product: Iron(III) Oxide Rust

  10. The Description of Changes • More than what can be observed • Ex. “bubbles are formed”, does not tell what gas is formed • A Chemical Equation is how we represent the changes taking place in a reaction • Word equations are the simplest way to describe reactants and products • An arrow, between reactants and products, represents change • + signs are used to separate reactants and to separate products

  11. Word Equations • Example: The combining of Vinegar (acetic acid) and Baking soda results in a vigorous reaction, forming a bubbly product The word equation: Vinegar + Baking Soda  Sodium acetate + water + Carbon Dioxide

  12. Chemical Equations • Shorter than word equations • more exact and specific • Replace the names of the substances with their chemical formulas Example: (the previous reaction) HC2H3O2 + NaHCO3 NaC2H3O2 + H2O + CO2 (Vinegar) Sodium Sodium Acetate water Carbon dioxide Acetic acid Hydrogen Carbonate • By examining the equation you can determine EXACTLY what elements are involved and how many atoms of each

  13. Writing Basic Chemical Equations • Replace the names of the substances with their chemical formulas • (remember; use oxidation numbers to form stable octets and write compound formulas) • Write the chemical equation with all reactants on one side, separated by a (+) sign • Draw an arrow pointing toward the products , also separated by a (+) sign. (recall diatomic elements) • Add symbols next to each compound, indicating physical state of matter (solid-s, liquid-l, gas-g)

  14. Write Chemical Equations; Practice • Sodium metal + chlorine gas sodium chloride crystals Answer: Na (s) + Cl2 (g) NaCl(s) Reactants Product

  15. Write Chemical Equations; Practice • Propane gas + oxygen  carbon dioxide + water + energy Answer: C3H8(g) + O2(g)  CO2 +H2O(g) + energy

  16. Write Chemical Equations; Practice • Zinc metal + hydrochloric acid  zinc chloride solution + hydrogen Answer: Zn(s) + HCl(aq)  ZnCl2(aq) +H2(g)

  17. Additional Practice • Hand out #’s 26-30 - with partner (10 min) • Post answers! • Handout #’s 31-35 – with partner (8 min) • Post answers! • Exit Ticket on your own! • Complete #36-50 for homework!

  18. Balancing Chemical Equations What is Balancing Equations? • Ensuring every atom in the reactants is present in the products in the same numberand type! Why? Law of Conservation of Matter: matter is neither created or destroyed, just transformed from one form to another No creation, no destruction, just rearrangement! Same Number and Type of Atoms

  19. Balancing Chemical Equations Steps of process: • Write the chemical equation with all reactants on one side, separated by a (+) sign • Draw an arrow pointing toward the products , also separated by a (+) sign. (recall diatomic elements) • Add symbols next to each compound, indicating physical state of matter (solid-s, liquid-l, gas-g) • Count the numbers of each type of element from each side of the equation. • List the symbols and numbers of each. • Change the coefficients as needed to ensure conservation of matter. (numbers and types equal)

  20. Example of Process • Chemical equation for aqueous magnesium chloride plus silver nitrate solution making aqueous magnesium nitrate and solid silver chloride: • Add symbols for physical state • MgCl2(aq) + AgNO3(aq) Mg(NO3)2(aq) + AgCl(s) • Count number and type of elements on each side Matter is not conserved! Numbers are different!

  21. Practice: Count the number of Atoms • Complete HO 1-10 (pairs) (20 min)

  22. Last Step Change the coefficients as needed to ensure conservation of matter. MgCl2(aq) + AgNO3(aq)Mg(NO3)2(aq) + AgCl(s) Atoms in reactants Atoms in products Mg- 1 Mg- 1 Cl- 2 Cl- 1 -2 Ag- 1 -2 Ag- 12 N-1 - 2 N-2 O- 3 -6 O- 6 How can I change the coefficients to make then the same? • A 2 added before the AgNO3(aq) in the reactants, will balance both N and O • Another 2 added before AgCl(s) in the products will balance both the Ag and Cl MgCl2(aq) + 2 AgNO3(aq)  Mg(NO3)2 (aq) + 2 AgCl(s)

  23. Predicting Oxidation Numbers • The total charge on the ion is known as the Oxidation Number of the atom Some metals have the same oxidation number in all compounds • Group 1 elements , oxidation number = 1+ • Group 2 elements , oxidation number = 2+ • Aluminum, oxidation number = 3+ • Groups 3-12 Many have more than one oxidation # depending on the reaction • Group 13 elements have 3 valence electrons, oxidation # =3+ • Group 14 may have 2+ or 4+ oxidation number • Groups 15, 16 and 17 tend to gain electrons since they are already ½ full • Their oxidation numbers are 3-, 2-, and 1- respectively

  24. Write a Balanced Equation for Each of These Reactions • Sodium metal + chlorine gas sodium chloride crystals • Propane gas + oxygen  carbon dioxide + water + energy • Zinc metal + hydrochloric acid  zinc chloride solution + hydrogen Remember: • use the oxidation numbers to construct octets and determine formula compounds • Use your reference sheets for names of ionic substances and covalent molecules. (check for diatomic molecules)

  25. Answers • balance equations for ppt #1.docx • balance equations for ppt #2.docx • balance equations for ppt #3.docx

  26. Answers 1Na (s) + Cl2 (g) NaCl(s) Atoms reactants Atoms products • Na – 1 Na – 1 • Cl – 2 Cl - 1 • Add coefficient of 2 to NaCl to balance Cl • Add coefficient of 2 to Na to balance Na 2 Na (s) + Cl2 (g)  2 NaCl(s)

  27. Answers Diatomic molecule • 2. C3H8(g) + O2(g)  CO2 +H2O(g) + energy • Propane from reference sheet • Atoms reactants Atoms products • C – 3 C – 1 3 • H – 8 H – 2 8 • O – 2 10 O – 3 6 10 • Add coefficient of 4 to H2O to balance H • Add coefficient of 3 to CO2 in product to balance C • Add coefficient of 5 to O2 in reactants to balance O • C3H8(g) +5 O2(g)  3 CO2 + 4 H2O(g) + energy • Now it is balanced! Matter was conserved!

  28. Answers • 3. Zn(s) + HCl(aq)  ZnCl2(aq) +H2(g) • Diatomic molecule • Atoms reactants Atoms products • Zn– 1 Zn– 1 • H – 1 2 H – 2 • Cl – 1 2 Cl - 2 • Add coefficient of 2 to HCl to balance H and Cl • Zn(s) + 2 HCl(aq)  ZnCl2(aq) +H2(g) • Now it is balanced! Matter was conserved!

  29. Let’s Use the Internet to Help us Practice! • Using a computer, Your Brain and your Newly Acquired Skills, practice balancing • Complete at least 10 equations from the beginner level, then 10 at the intermediate level. • Then try 2 or three advanced ones! • Track your progress and record the number of trials it took for each equation in your notebook! • Complete an exit ticket, indicating how many tries it took for each equation • Leave your exit ticket on the laptop cart when you have put your computer away properly!

  30. More Balancing! • Access the Following Site: • http://education.jlab.org/elementbalancing/index.html • At least 10 Beginner equations and 10 Intermediate!

  31. Exit Ticket • Complete an exit ticket, indicating how many tries it took for each equation. 2. Leave your exit ticket in the box AFTER you have put your computer away properly!

  32. Other Sites You Can Use To Practice • http://chemistry.csudh.edu/lechelpcs/rxnbalancingcsn7.html (pretty good, hard but shows solutions after 3 tries) • http://funbasedlearning.com/chemistry/chemBalancer • http://www.sciencegeek.net/Chemistry/taters/EquationBalancing.htm (All at Once)

  33. Types Of Reactions • There are 5 major types of chemical reactions • Synthesis • Decomposition • Single displacement • Double displacement • Combustion • Reactions can be categorized by recognizing patterns which occur.

  34. Synthesis • Pattern to recognize synthesis • Whenever two or more substances combine to form a single product, the reaction is synthesis.

  35. Decomposition • Pattern to recognize synthesis • Whenever a compound is broken down into two or more simpler substances it is a decomposition reaction.

  36. Single-Displacement Reaction • Pattern to recognize single displacement • Whenever one element takes the place of another in a compound, it is a single displacement reaction.

  37. Let’s Classify these reactions! • 2 Na + Cl2  2NaCl • PCl5  PCl3 + Cl2 • 2Al + Fe2O3  2Fe + Al2O3 • 2Ag2O  4Ag + O2 • Cl2 + 2KBr  2KCl +Br2 • CaO + SiO2  CaSiO3

  38. Answers • 2 Na + Cl2  2NaCl 2 substances combine so it is synthesis! 2. PCl5  PCl3 + Cl2 A single compound is broken down into two simpler substances- it is decomposition! 3. 2Al + Fe2O3  2Fe + Al2O3 One element takes the place of another, it is single displacement!

  39. Answers Continued • 2Ag2O  4Ag + O2 Decomposition • Cl2 + 2KBr  2KCl +Br2 Single-displacement • CaO + SiO2  CaSiO3 Synthesis

  40. Double-Displacement Reactions • Pattern to recognize a double-displacement • Whenever the positive ions of two ionic compounds are interchanged, it is a double displacement reaction. • At least one product must be a precipitate of water!

  41. Combustion Reaction • Pattern to recognize combustion • Whenever a substance combines rapidly with OXYGEN to form one or more oxides, is a combustion reaction.

  42. Let’s Apply what we have learned! • Classify these reactions: • PbCl2 + Li2SO4  PbSO4 + 2LiCl • CH4 + 202  CO2 + 2H2O • C6H1206 + 602 6CO2 + 6H2O • BaCl2 + H2SO4  2HCl +BaSO4

  43. Answers • PbCl2 + Li2SO4  PbSO4 + 2LiCl Interchanged cations, so Double-displacement • CH4 + 202  CO2 + 2H2O substance combines with Oxygen and forms an oxide, so Combustion • C6H1206 + 602 6CO2 + 6H2O Combustion • BaCl2 + H2SO4  2HCl +BaSO4 Double-displacement

  44. Compare and Contrast Types Of Reactions

  45. Identify these Reactions as one of the five types studied • A + BX AX +B • AB  A+B • AXZ  AX + Z • AB + CD  AC + BD • BC + D  BD + C • BD + oxygen  B oxide + D + water • AD + XY  AY + DX • +  +

  46. Answers • Single displacement (AKA single replacement) • Synthesis • Decomposition • Double Displacement (AKA Double replacement) • Single Displacement (AKA Single replacement) • Combustion • Double Displacement (AKA Double replacement) • Decomposition

  47. Factors that Affect Direction Of Reactions • External factors modify the direction of reactions • Many can change direction: Called Reversible • Like charging and draining a battery • Adding or removing energy as heat can affect direction • Endothermic reactions; added heat pushes reaction to the right • Exothermic reactions; added heat pushes the reaction to the left

  48. Reversibility of Reactions • Not all reactions are reversible • Like fuel burns, food is digested and paint hardens • New products are formed and at least one reactant is used up • Some reactions automatically reverse to establish equilibrium • No net (overall) change • Reactants and products change place, forming at about the same rate • Reactants are never used up because they are always being used then reformed from products • Ex. CaCo3 CaO + CO2

  49. Initiating a Reaction • For a reaction to occur, particles must collide with sufficient force to cause electrons to rearrange. • The amount of energy needed to cause a reaction is called Activation Energy • Slow reactions have high activation energy • To determine reaction rate, measure how quickly one reactant disappears or one product appears

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