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Unit 8 – Chemical Equations and Reactions

Unit 8 – Chemical Equations and Reactions. Notes p.1-2 These ones are in order!. Format of Chemical Equations:. 2H 2 + O 2  2H 2 O Reactants/Reagents. Format of Chemical Equations:. 2H 2 + O 2  2H 2 O Product(s). Format of Chemical Equations:.

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Unit 8 – Chemical Equations and Reactions

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  1. Unit 8 – Chemical Equations and Reactions Notes p.1-2 These ones are in order!

  2. Format of Chemical Equations: 2H2+ O2 2H2O Reactants/Reagents

  3. Format of Chemical Equations: 2H2+ O2 2H2O Product(s)

  4. Format of Chemical Equations: 2H2+ O2 2H2O Yield(s)

  5. Format of Chemical Equations: 2H2+ O22H2O Subscript(s)

  6. Format of Chemical Equations: 2H2+ O2 2H2O Coefficients(s)

  7. Format of Chemical Equations: • Coefficients • Large numbers in front • Give how many moleculesof each substance are in the equation • Subscripts • Small numbers after an element • Give how many of eachatomare needed in the formula

  8. Now for some practice • These are not in the notes but are essential skills to have

  9. What is the coefficient for … • 2Al + 3CuSO4 Al2(SO4)3 + 3Cu • Aluminum: 2 • Copper sulfate: 3 • Aluminum sulfate: 1 (when there is no number written, it is 1) • Copper: 3

  10. What is the coefficient for … • 2H2O  2H2 + O2 • Water: 2 • Hydrogen gas: 2 • Oxygen gas: 1

  11. How many ___ are there in ___ • Mg(OH)2 + 2HCl  MgCl2 + 2H2O • How many H are in Mg(OH)2? • 2 (distribute the subscript through the parentheses) • How many H are in HCl? • 2 (the coefficient means there are 2 H) • How many H are in the reactants? • 4 total: 2 from HCland 2 from Mg(OH)2 • How many H are in the products? • 4 (all from H2O)

  12. Law of Conservation of mass • Matter cannot be created nor destroyed, only change form • Balancing Equations • Must be the same number of each type of atom on the reactant side and the product side Even though a reaction has taken place, the mass at the beginning and the mass at end are the same. No mass (or matter) is gained or lost in the reaction.

  13. Never change SUBSCRIPTS in balancing!! Only change COEFFICIENTS!!!

  14. To Balance an Equation: 1. Totalthe number of each element for both sides 2. Check if each element is the same on both sides 3. Change the total on the inventory list so that the number of atoms matches. 4. Add a coefficient to the substance in the equation 5. Adjust the inventory list to reflect any changes in other atoms 6. Move on to each atom until the lists match for EVERY element

  15. Tricks: • Balance polyatomic ions as a group • If an element is present twice on one side, leave it for last • If the list isn’t working because you have an odd number on one side and an even number on the other, try doubling everything • Simplify: Check after balancing for any factor that could divide through all the coefficients

  16. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr Br2 + NaCl Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2 • 1. Total the number of each element for both sides • Look at subscripts to tell how many are in the unbalanced equation • All coefficients in an unbalanced equation are 1 (You might need to brush up on writing chemical formulas if you are only given the name.)

  17. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr Br2 + NaCl Cl: 2 ≠ Cl: 1 Na: 1 = Na: 1 Br: 1 ≠ Br: 2 2. Check if each element is the same on both sides - Chlorine and bromine are unbalanced

  18. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr Br2 + NaCl Cl: 2 ≠ Cl: 1 2 Na: 1 = Na: 1 Br: 1 ≠ Br: 2 3. Change the total on the inventory list so that the number of atoms matches. - I like to start with the first element on my inventory list. It doesn’t really matter which one you start with.

  19. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr Br2 + 2NaCl Cl: 2 ≠ Cl: 1 2 Na: 1 = Na: 1 Br: 1 ≠ Br: 2 4. Add a coefficient to the substance in the equation - 1 x coefficient = 2, therefore the coefficient is 2

  20. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr Br2 + 2NaCl Cl: 2 = Cl: 1 2 Na: 1 ≠ Na: 1 2 Br: 1 ≠ Br: 2 5. Adjust the inventory list to reflect any changes in other atoms - The new coefficient applies to both Na and Cl. According to the equation, there are now 2 Na in the products.

  21. EXAMPLE: WRITE A BALANCED EQUATION • Chlorine + sodium bromide  bromine + sodium chloride Cl2 + 2NaBr Br2 + 2 NaCl Cl: 2 = Cl: 1 2 Na: 1 2= Na: 1 2 Br: 1 2 = Br: 2 6. Move on to each atom until the lists match for EVERY element - Na is now unbalanced. The new coefficient in front of NaBr should be 2. That means there are now also 2 Br. The equation is balanced!

  22. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + CaCl2 AlCl3 + CaSO4 Al: 2 Al: 1 SO4: 3 SO4: 1 Ca: 1 Ca: 1 Cl: 2 Cl: 3 • 1. Total the number of each element for both sides • Look at subscripts to tell how many are in the unbalanced equation • All coefficients in an unbalanced equation are 1 Trick: Because SO4 is present as a polyatomic ion on both sides, it (sulfate) can be treated as one unit instead as S and O separately.

  23. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + CaCl2 AlCl3 + CaSO4 Al: 2 ≠ Al: 1 SO4: 3 ≠ SO4: 1 Ca: 1 = Ca: 1 Cl: 2 ≠ Cl: 3 2. Check if each element is the same on both sides - Aluminum, sulfate, and chlorine are unbalanced

  24. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + CaCl2 AlCl3 + CaSO4 Al: 2 = Al: 12 SO4: 3 ≠ SO4: 1 Ca: 1 = Ca: 1 Cl: 2 ≠ Cl: 3 3. Change the total on the inventory list so that the number of atoms matches. - I like to start with the first element on my inventory list. It doesn’t really matter which one you start with – but do one at a time!

  25. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + CaCl2 2AlCl3 + CaSO4 Al: 2 = Al: 12 SO4: 3 ≠ SO4: 1 Ca: 1 = Ca: 1 Cl: 2 ≠ Cl: 3 4. Add a coefficient to the substance in the equation - 1 x coefficient = 2, therefore the new coefficient is 2. Now Al is balanced.

  26. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + CaCl2 2AlCl3 + CaSO4 Al: 2 = Al: 12 SO4: 3 ≠ SO4: 1 Ca: 1 = Ca: 1 Cl: 2 ≠ Cl: 36 5. Adjust the inventory list to reflect any changes in other atoms - The new coefficient applies to both Al and Cl. According to the equation, there are now 6 Cl in the products (2 from coefficient x 3 from subscript).

  27. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + 3 CaCl2 2 AlCl3 + CaSO4 Al: 2 = Al: 1 2 SO4: 3 ≠ SO4: 1 Ca: 1 = Ca: 1 Cl: 26 = Cl: 3 6 6. Move on to each atom until the lists match for EVERY element - Cl in the reactants is now unbalanced. There need to be 6. 2 x coefficient = 6, so the coefficient for CaCl2needs to be 3. Now Cl is balanced.

  28. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + 3 CaCl2 2 AlCl3 + CaSO4 Al: 2 = Al: 1 2 SO4: 3 ≠ SO4: 1 Ca: 13 = Ca: 13 Cl: 2 6 = Cl: 3 6 6. Move on to each atom until the lists match for EVERY element - Changing the coefficient of CaCl2 means there are now 3 Ca. To balance calcium we need to change the number in the products.

  29. EXAMPLE: WRITE A BALANCED EQUATION aluminum sulfate+ calcium chloride  aluminum chloride +calcium sulfate Al2(SO4)3 + 3 CaCl2 2 AlCl3 + 3 CaSO4 Al: 2 = Al: 1 2 SO4: 3 = SO4: 13 Ca: 1 3 = Ca: 1 3 Cl: 2 6 = Cl: 3 6 6. Move on to each atom until the lists match for EVERY element - Calcium now balances! The new coefficient means there are three sulfates. Now sulfate balances!

  30. HINTS 4 3 1 5 Balance oxygen LAST! 3 2 2 Practice Problems ___ C3H8 + ___ O2___ CO2 + ___ H2O ___ NaBrO3  ___ NaBr + ___ O2 ___ NH4NO3___ N2O + ___ H2O ___ H2 + ___ CO + ___ O2 ___ H2CO3 ___ La2O3 + ___ H2O  ___ La(OH)3 ___ NaI + ___ Pb(NO3)2 ___ NaNO3 + ___PbI2 1 1 2 Balance oxygen LAST! Make sure to account for both N in the reactants. 1 1 1 1 It was already balanced! Yay! 1 3 2 Balance oxygen LAST! 2 1 2 1 Treat the nitrate ion as one unit.

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