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If we ’ re going to do chemical reactions with antacids, we ’ d better know how to write them!

Unit 2B. Section 2.6. If we ’ re going to do chemical reactions with antacids, we ’ d better know how to write them!. O. O. H. H. H. H. What is a Chemical Reaction?. Bonds are broken and atoms are rearranged to form new compounds. 2 H 2 + O 2  2 H 2 O.

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If we ’ re going to do chemical reactions with antacids, we ’ d better know how to write them!

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  1. Unit 2B Section 2.6 If we’re going to do chemical reactions with antacids, we’d better know how to write them!

  2. O O H H H H What is a Chemical Reaction? Bonds are broken and atoms are rearranged to form new compounds. 2 H2 + O2 2 H2O Watch as 2 H2 and 1 O2 undergo a chemical reaction

  3. O O H H H H O O H H H H Chemical Reactions Bonds and atoms are rearranged to form new compounds. 2 H2 + O2 2 H2O The compounds in the end are different from those in the beginning Bonds are broken and formed between different atoms

  4. What is a Chemical Reaction? • When bonds of substances are broken and atoms rearrange to form new substances • Also known as a chemical change 2 H2 + O2 2 H2O

  5. Observations (Indicators) of a Chemical Reaction(change) • Color change • Odor change • Gas production • Precipitate formation: insoluble solid that is formed when 2 • aqueous solutions are reacted • Temperature change • Exothermic Reactions: reactants release heat • & temp. of reaction • increases • Endothermic Reactions: reactants absorb heat • energy & temp. of reaction • decreases

  6. What are Chemical Equations? • The “sentence” of chemistry • Uses chemical formulas & other symbols instead of words to show a chemical reaction Reactants Products What you start with What you end with NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq) Arrow : Read as: Yields, Produces, Forms Physical State s = solid l = liquid g = gas aq = aqueous (dissolved in water)

  7. Formula equation: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g) Examples of Chemical Equations Word equation: Magnesium metal is reacted with aqueous hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas  Visualization

  8. Writing Chemical Equations • You must write the correct chemical formula for each reactant & product (Section 2.2) • “and”, “is mixed with” or “reacts with” = + • “yield”, “produces” and “forms” =  • Remember “BrINClHOF”: to represent the 7 diatomic elements that have a subscript of 2 in their chemical formula • Br2 I2 N2 Cl2 H2 O2 F2

  9. Let’s Practice #1 Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas Example: Write the word equation into symbol form

  10. Let’s Practice #1 Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas Example: Write the word equation into symbol form Al + HCl  AlCl3 + H2

  11. Let’s Practice #2 Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate Example: Write the word equation into symbol form

  12. Let’s Practice #2 Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate Example: Write the word equation into symbol form Cu(NO3)2 + NaOH  Cu(OH)2 + NaNO3

  13. Synthesis(Combination): when 2 or more substances combine to form a SINGLE substance Element + Element  Compound Cu + S CuS Compound + Compound  Compound Li2O + H2O LiOH

  14. Decomposition: when 1 substance breaks apart into 2 or more substances; requires Energy to initiate Compound  Element + Element CaS  Ca+ S Compound  Compound + Compound H2O2 H2O+ O2

  15. Single Replacement: when a more reactive element replaces a less reactive element in a compound Compound + Element  Element + Compound AgI + K  Ag + KI

  16. Double Replacement:when the positive ions of each aqueous compound replace each other +  + Compound + Compound  Compound + Compound KI + AgNO3  AgI + KNO3

  17. Combustion:reaction of an element or compound with OXYGEN to form an oxide & produce heathydrocarbons combust to always produce carbon dioxide,water & heat Mg + O2 MgO CH4 + O2  CO2 + H2O

  18. Section 2.7—Balancing Equations We need to finish writing those equations we started!

  19. Law of Conservation of Mass Matter cannot be created nor destroyed just changed in form. Thus mass must remain constant through changes.

  20. Conservation of Mass CaCl2 + Na2SO4 CaSO4 + 2NaCl Mass before(reactants) = mass after(products) # atoms before (reactants) = # atoms after(products)

  21. How Does the Law Lead to Balancing? • Matter cannot be created nor destroyed • during a chemical or physical change. • The number of atoms of each element • must be the same on both sides • To ensure this we must balance the • equation .

  22. How Do We Begin? Start by Counting the Atoms of each Substance • Subscripts tell you how many atoms • Coefficients are always multiplied by subscripts • With a parentheses, inner & outer subscripts are always multiplied together

  23. Try These! Count the atoms in each compound (a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___ (b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___

  24. How Do We Balance Equations? Practice Problems: How many atoms of each type are indicated in the following compounds? (a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___ (b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___ (c) 3 Ca(NO3)2 Ca= ___ N= ___ O= ___ 6 24 2 8 4 8 12 8 3 6 18

  25. Coefficients are added to change the number of atoms in a substance! CH4 + 2 O2 CO2 + 2 H2O Total: 1 C 4 H 4 O Total: 1 C 4 H 4 O The equation is balanced.

  26. How to Balance Chemical Equations: 1 Make a table of elements +  _____ + _____ C H4 _____ O2 H2 O _____ C O2 Reactants Products C H O

  27. How to Balance By Inspection: 2 Count the number of each element or ion on the reactants and products side. Don’t forget to add all the atoms of the same element together—even if it appears in more than one compound! +  _____ + _____ C H4 _____ O2 H2 O _____ C O2 Reactants Products C 1 1 H 4 2 O 2 3

  28. How to Balance By Inspection: 3 Use coefficients to balance the numbers Each time you add a coefficient, update your table with the new quantities of each atom. +  + _____ C H4 _____ 2 O2 _____ 2 H2 O _____ C O2 Reactants Products C 1 1 H 4 2 4 O 2 3 4 4

  29. How to Balance By Inspection: OPTIONALPlace a “1” in any empty coefficient location 4 Filling each coefficient location lets you and the grader know that you finished the problem rather than you left some blank because you weren’t done! +  + _____ 1 C H4 _____ 2 O2 _____ 2 H2 O _____ 1 C O2 Reactants Products C 1 1 H 4 2 4 O 2 3 4 4

  30. Choosing the Order of Balancing How do you know what order to balance in? StartElements that appear only 1 time per side Save for later Elements that are uncombined Pb + PbO2 + H+ Pb2+ + H2O StartElements in most complicated molecules To balance this equation, use the order: O, H, Pb

  31. How is Balancing Affected by Order? What happens if we balance in the order determined in the last slide? O, H, Pb + Pb O2 +  + _____ 1 Pb _____ 1 _____ 4 H+ _____ 2 H2 O _____ 2 Pb2+ Reactants Products O 2 1 2 H 1 4 2 4 Pb 2 1 2

  32. What about a different order? How is it different if we balance in a different order? H, O, Pb 4 + Pb O2 +  + _____ 1 Pb _____ 1 _____ 2 H+ _____ 2 H2 O _____ 2 Pb2+ Reactants Products  H 1 2 4 2 4 O 2 1 2 Pb 2 1 2 You’ll still get to the correct answer, but it will take longer and be more complicated!

  33. Do You Remember Polyatomic Ions? Polyatomic ion– Group of atoms that together has a net charge e.g. Nitrate NO31- Carbonate CO32-

  34. Balancing with Polyatomic Ions: 1 Make a table of elements Hint: Chunk the polyatomic ions—IF they appear on both sides OH is a polyatomic ion that is sometimes “hidden” in H2O. Re-write H2O as HOH to “see” the OH polyatomic ion. H OH _____ + (OH)2  + H3 PO4 _____ Ca _____ Ca3 (PO4)2 _____ H2 O Reactants Products H PO4 Ca OH

  35. Balancing with Polyatomic Ions: Count the number of each element or ion on the reactants and products side. 2 H OH + (OH)2  + _____ H3 PO4 _____ Ca _____ Ca3 (PO4)2 _____ H2 O Reactants Products H 3 1 PO4 1 2 Ca 1 3 OH 2 1

  36. Balancing with Polyatomic Ions: 3 Add coefficients to balance the numbers H OH + (OH)2  + _____ 2 H3 PO4 _____ 3 Ca _____ Ca3 (PO4)2 _____ 6 H2 O Reactants Products H 3 6 1 6 PO4 1 2 2 Ca 1 3 3 OH 2 6 1 6

  37. Balancing with Polyatomic Ions: 5 Place a “1” in any empty coefficient location H OH + (OH)2  + _____ 2 H3 PO4 _____ 3 Ca _____ 1 Ca3 (PO4)2 _____ 6 H2 O Reactants Products H 3 6 1 6 PO4 1 2 2 Ca 1 3 3 OH 2 6 1 6

  38. Let’s Practice #1 Example: Balance the following equation __ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O

  39. Example: Balance the following equation Did you see the “OH” polyatomic ion & change H2O to HOH? 2 1 1 2 __ HCl + __ Ca(OH)2 __ CaCl2 + __ H2O HOH

  40. Let’s Practice #2 Example: Balance the following equation __ H2 + __ O2 __ H2O

  41. Example: Balance the following equation 2 1 2 __ H2 + __ O2 __ H2O

  42. Example: Balance the following equation Let’s Practice #3 __ Fe + __ O2 ___ Fe2O3

  43. Example: Balance the following equation 4 3 2 __ Fe + __ O2 ___ Fe2O3

  44. Practice Problems • 1. 2 5 4 2 combustion • 2. 1 1 1 1 SR • 3. 1 2 2 1 SR • 4. 2 2 1 decomp • 5. 1 1 1 synthesis • 6. 16 1 8 synthesis • 7. 1 1 1 2 DR • 8. 4 3 4 3 SR

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