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Chemical Reactions Balancing Equation Steps

Learn the steps to balance chemical equations including synthesis, decomposition, single replacement, and double replacement reactions. Understand the process, examples, and special scenarios.

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Chemical Reactions Balancing Equation Steps

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  1. Chapter 10 Chemical Reactions

  2. Balancing Chemical Equations Steps for Balancing Equations • Write the skeleton equation • Use arrows, +/- & physical states of matter 2. Count the atoms of the reactants 3. Count the atoms of the products 4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation NEVER, NEVERCHANGE THE SUBSCRIPT 5. Write the coefficients in their lowest possible ratio

  3. Count the reactants & products Balance the H & O atoms with coefficients for the reactants to = the products

  4. YOU'RE NOT DONE !! Add the physical states of the elements Now you have a happy equation

  5. Types of Reactions Synthesis Reaction A chemical reaction in which 2 or more reactants produce 1 product General form A + B  AB In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.

  6. Synthesis Reaction • Examples • 2Na + Cl2 2NaCL • 2Mg + O2  2MgO • 4Al + 3O2  2Al2O3 • H20 + SO3  H2SO4 (this is one cause of acid rain) • H20 +CO2  H2CO3 (this is why rainwater is naturally acidic) • H2O + MgO  Mg(OH)2

  7. Synthesis (combin.) Reaction Special CASE “Scenarios” for these RXN’s Metallic oxide + Water  Base Na2O + H2O  2NaOH Non-Metallic oxide + Water  Acid SO3 + H2O  H2SO4

  8. Synthesis (combin.) Reaction Special CASE “Scenarios” for these RXN’s Metallic oxide + CO2 Metal carbonate CaO + CO2 CaCO3 Metal chloride + Oxygen  Metal chlorate 2KCl + 3O2 2KClO3

  9. Decomposition Reaction A chemical reaction where 1 compound, breaks apart into 2 or more simpler products General form AB  A + B In this cartoon the egg (the reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances.

  10. Decomposition Reaction • Examples • 2 H2O  2H2 + O2 • 2HgO  2Hg + O2 • 2Ag2O  4Ag + O2 • CaCO3  CaO + CO2 • H2CO3  H2O + CO2 • Decomposition reactions often require an energy source: • Heat • Light • Electricity

  11. Decomposition Reaction Special CASE “Scenarios” for these RXN’s Heating an acid  non metallic oxide + water Heating a base  metallic oxide + water Heating a carbonate  oxide + CO2 Heating a metal chlorate  chloride + O2 Heating a metallic oxide  Metal + O2 Heating a sulfite  Metal oxide + SO2 These are just the reverse of their synthesis RXN’s

  12. Single Replacement Reaction A reaction in which atoms of one element replace the atoms of another element that is part of a compound Notice, the guy in the orange shirt steals the date of the other guy. So, a part of one of the reactants trades places and is in a different place among the products

  13. Single Replacement Reaction 1. Cations replace Cations General Form AB + C  CB + A C would be the cation/metal and so replaced A, which would have to be a cation 2. Anions replace Anions General Form DE + F  DF + E F would be the anion/non-metal and so replaced E, which would have to be a anion

  14. Single Replacement Reaction • Examples: • Cu + AgNO3 Cu(NO3)2 + Ag • Cation replaces Cation • NaI + Cl2 NaCl + I2 • Anion replaces Anion

  15. Single Replacement Reaction Special situations for SR RXN’s 1. Activity Series Definition  A list of metal/cations in order of decreasing reactivity Used to determine if one metal can replace another in a RXN The higher its position on chart the more metals it can replace Ex: sodium will replace aluminum The lower its position on the chart the less metals it can replace Ex: zinc will not replace magnesium

  16. Single Replacement Reaction Special situations for SR RXN’s • Water  for writing RXN’s it may be useful to write water • as H(OH). Why? • Halogens • The halogens also have a series; As you go down group 17 they decrease in reactivity Ex: Chlorine cannot replace fluorine but it can replace bromine

  17. Single Replacement Reaction Special situations for SR RXN’s Do the following reactions occur? Explain. Zn + H2SO4 H2 + ZnSO4 Sn + 2NaNO3 Sn(NO3)2 + 2Na 2NaCl + F2  2NaF + Cl2 CaCl2 + I2 CaI2 + Cl2

  18. Double Replacement Reaction A reaction where there is an exchange of cations between 2 ionic compounds Notice how the first guy exchanged hats with the second guy, so they are both wearing each other's hat.

  19. Double Replacement Reaction General Form AB + CD  AD + CB ** Make sure of cation and anion placement Ex: BaCl2 + K2CO3 BaCO3 + 2KCl 3KOH + H3PO4 3H(OH) + K3PO4

  20. Double Replacement Reaction “Driving Forces” allow a RXN to take place Use your net ionic equation to see if one of the following are formed “Driving Forces” in double replacement RXN’s One of three things must form for these RXN’s to occur 1. A molecular compound like water forms • A gas forms that bubbles out i.e. • (H2, CO2, H2S, CO, etc.) 3. A precipitate forms

  21. Double Replacement Reaction How do you know if something is a precipitate? 1. It is insoluble or slightly soluble in water 2. Check your solubility chart Examples: will these RXN’s occur? Explain BaCl2 Soluble….NR AgCl Insoluble….Yes Ca3(PO4)2 Insoluble….Yes NaNO3 Soluble….NR

  22. Double Replacement Reaction Examples: will these RXN’s occur? FeS(s) + HCl(aq)  FeCl2(aq) + H2S ↑ Yes Pb(NO3)2 (aq) + 2KI (aq)  2KNO3 (aq) + PbI2 ↓ Yes FeCl3(aq) + Al(NO3)3(aq)  Fe(NO3)3(aq) + AlCl3(aq) No…soluble … no “driving force” present

  23. Combustion Reactions Definition: Oxygen reacts with another substance often producing energy in the form of heat and light General form: CxHy + O2 CO2 + H2O Types: 1. Complete combustion Definition: If sufficient oxygen is present to burn completely Hydrocarbons combine with oxygen to produce carbon dioxide and water

  24. Combustion Reactions 2. Incomplete combustion Definition: Insufficient oxygen is present to burn completely Hydrocarbons combine with oxygen to produce poisonous carbon monoxide and solid elemental carbon as well as carbon dioxide and water Examples:

  25. Extra “Special” RXN’s • Reactive metals and water (SR) • Group 1 and 2 metals react to form a metal hydroxide and hydrogen gas • Acid and a Base • React to form a salt (ionic compound composed of the anion of the acid and the cation of the base) and water

  26. Aqueous SLN • When two (aq) solutions that contain ions as solutes combine…. • The ions may react with one another • The H20 molecules don’t usually react • The three types of products can form aka “driving forces” …. Gas, water, or precip • Chemical equations do not always show all that happens in a RXN

  27. Net Ionic Equations • Solutions are composed of • Solute • Solvent • Aqueous SLN • Is a sln in which the solvent is water

  28. Net Ionic Equations • Substances that are ions in a solution and are written as such • These equations show all of the particles in a solution as they “really” exist • Some ions are in both the RXT & PROD, these are called… • SPECTATOR IONS

  29. Net Ionic Equations • SPECTATOR IONS - dissociation only occurs if it is in an aqueous solution • S, L, G are not ions see your solubility chart

  30. Net Ionic Equations • Regular equation • 2NaOH (aq) + CuCl2 (aq)  2NaCl (aq) + Cu(OH)2(s) • Ionic equation • 2Na+ (aq) + 2OH- (aq) + Cu+2(aq) + 2Cl- (aq)  2Na+(aq) + 2Cl- (aq) + Cu(OH)2 (s)

  31. Net Ionic Equations • Net Ionic equation • 2OH- (aq) + Cu+2(aq)  Cu(OH)2 (s) • Net ionic equation is formed when all of the spectator ions are cancelled

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