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Chemistry SM-1131 Week 9 Lesson 1

Chemistry SM-1131 Week 9 Lesson 1. Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008. Class Today. Tests Chemical Reactions Types of Chemical Reactions Balancing Chemical Reactions Solubility Precipitation Reactions. Tests.

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Chemistry SM-1131 Week 9 Lesson 1

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  1. Chemistry SM-1131Week 9 Lesson 1 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008

  2. Class Today • Tests • Chemical Reactions • Types of Chemical Reactions • Balancing Chemical Reactions • Solubility • Precipitation Reactions

  3. Tests • There are still people needing to take tests. • They will hopefully be handed back on Friday • The range was huge. A handful of you really aced that last test. There was a small section of Bs. There was a large section of 60-79, and then there were a handful of 10-30. • We’ll go over it soon. • WIKI EXTENSION UNTIL NEXT WEDNESDAY

  4. Chemical Reactions • A chemical reaction is a rearrangement of atoms. • Reactants  Products • Once a reaction has happened chemists often want to collect 1 of the products. Often times we’ll use solubility to help us… we’ll see how that works in a sec.

  5. Evidence of a Chemical Reaction • Heat and Light • Formation of solids • Gas emitting • Changing colors • Change in temperature

  6. Some quick vocab • (g) means the substance is a gas • (l) means the substance is a liquid • (s) means the substance is a solid • (aq) means the substance is aqueous • Aqueous means dissolved in water, which does not necessarily mean the compound was a liquid. Ethanol and sugar both become aqueous, but only one of them was a solid at room temperature.

  7. Rules about Chemical Equations • Remember that law of conservation of mass? • Matter can neither be created nor destroyed. • We have to follow that! • So, whatever mass we started with on the reactants side we’re going to have to have on the right side. • We do this by making sure reactions are balanced. Mean we have the same number and types of atoms on both sides of the .

  8. Counting molecules and atoms • 2H2O • 2 moles of water. To count atoms we’re going to use mutiplication. 2x2H= 4H, 2x1O= 2O • 4Mg(NO3)2 • 4x 1Mg= 1Mg, 4x2N = 8N, 4x6O= 24O • The 2 and the 4 are called coefficients, just like 5X in math where the 5 is the coefficient.

  9. Types of Chemical Reactions • There are 5 main types of reactions • Combination aka synthesis • Decomposition • Combustion • Single displacement • Double displacement • (Acid Base, gas evolution, precipitation, oxidation and reduction aka redox)

  10. Combination Reactions • 2 things come together to make 1 thing. • Carbon and Hydrogen react to form the compound methane. • C + H2 CH4 • This is called a skeleton equation since it’s not balanced. There is 1 C on the left, and 1C on the right, but there are 2H on the left and 4H on the right.

  11. Balanced Chemical Reaction • C + 2H2 CH4 • Note, when I’m talking about “things” I mean unique formulas. I recognize to balance this reaction it requires 3 moles or 3 molecules on the left, BUT, I’m only speaking about the “types of molecules,” and I’m not invoking the coefficients.

  12. Combination Reaction 2 • Mg and oxygen react at high temperature what is formed? • Mg + O2 MgO • O2 is diatomic when written into reactions (HINClBrOF) • (How’d I know MgO, well 4 steps: symbols, charges, switcheroo, reduce) • To balance it…

  13. Balancing Chemical Reactions • ___ Mg + ___ O2 ___MgO • 1- for all ionic compounds correctly establish their formula • 2-List all elements in the rxn under the arrow • 3-Count the number of atoms of each type on both sides of the equation • 4-Starting with metals change the coefficients until both sides are balanced. DO NOT CHANGE CHEMICAL FORMULAS.

  14. Balancing Chemical Reactions • ___ Mg + ___ O2 ___MgO ___Mg___ ___O___ • ___ Mg + ___ O2 ___MgO 1 Mg 1 2 O 1 NOT BALANCED • ___ Mg + ___ O2 _2_MgO 1 Mg 2 2 O 2 NOT BALANCED • _2_ Mg + ___ O2 _2_MgO 1 Mg 2 2 O 2 BALANCED

  15. More examples • N2 + 3H2 2NH3 • 2Al + 3F2  2AlF3 • P4 + 5O2  P4O10 • SO3 + H2O  H2SO4

  16. Decomposition • When things decompose they break down. This reaction is where 1 molecule breaks down into several molecules. • Iron(III) chloride decomposes at high temperature into it’s elements. • FeCl3 Fe + Cl2 • Not balanced, again HINClBrOF

  17. Decomposition • ___ FeCl3 ___Fe + ___Cl2 ___Fe___ ___Cl___ (count by atoms, not Cl2) • ___ FeCl3 ___Fe + ___Cl2 _1_Fe_1_ _3_Cl_2_

  18. Decomp. Cont. • _2_ FeCl3 ___Fe + _3_Cl2 _2_Fe_1_ _6_Cl_6_ • _2_ FeCl3 _2_Fe + _3_Cl2 _2_Fe_2_ _6_Cl_6_ • What’s the LCD of 3 and 2? 6 so Cl on both sides needs 6. So how many FeCl3? Cl2?

  19. Electrolysis of water • Electrolysis is when you put a current through water. Water turns into it’s elements. Write and balance the reaction. • ___H2O  ___H2 + ___O2 _2H 2 _1O_2 • _2_H2O  ___H2 + ___O2 _4H_2 _2O_2 • _2_H2O  _2_H2 + ___O2 _4H_4 _2O_2

  20. More examples of Decomposition • CaCO3 CaO + CO2 • 2 HgO  2 Hg + O2 • 2 ClO3  2KCl + 3O2

  21. Combustion Reactions • Combustion means burning and fire. What two things does fire require? O2 and something to burn. We normally burn hydrocarbons (Hydro=H, Carbon = C therefore stuff made up of H and C). • The products are always CO2 and H2O. • Methane and Oxygen burn write the equation. • ___CH4+ ___O2 ___ CO2 + ___H2O

  22. Balance a combustion • ___CH4+ ___O2 ___ CO2 + ___H2O __C __ __H __ __O __ (it comes from 2 places) Balance this reaction now

  23. Balanced Reaction • _1_CH4+ _2_O2 _1_ CO2 + _2_H2O 1_C 1_ 4_H 4_ 4_O 4_ (it comes from 2 places)

  24. Harder example • C2H6 + O2 CO2 + H2O 2 C 1_ 6 H 2_ 2 O 3_ • C2H6 + 3.5 O2 2 CO2 + 3 H2O 2 C 2_ 6 H 6_ 7 O 7_(no such thing as 0.5O2)

  25. Double all the coefficients • 2C2H6 + 7 O2 4 CO2 + 6 H2O 4 C 4_ 12 H 12_ 14 O 14_ All combustion reactions will be just like one of those two reaction.

  26. Displacements • These are the 2 hardest to tell apart when starting. • Single displacements typically have 1 lone element on both sides of the reaction • Double displacements look like the biggest reactions out there, and you’ll see that the two metals switch places

  27. Single Displacement • Magnesium metal starts making hydrogen gas when it’s dropped in aqueous hydrochloric acid. What’s the full reaction? ___Mg + ___HCl  ___ H2+ __ ?

  28. Single Displacement • ___Mg + ___HCl  ___ H2+ __ MgCl? • NO! 4 steps when writing ionic salts ALWAYS! So, it’s MgCl2 • ___Mg + ___HCl  ___ H2+ __ MgCl2 1 Mg 1_ 1 H 2_ 1 Cl 2_ ___Mg + _2_HCl  ___ H2+ __ MgCl2

  29. Single Displacement • ___Mg + _2_HCl  ___ H2+ __ MgCl2 • Notice: Mg is elemental on the left side, and Hydrogen is elemental on the right side. • The single lone element was displaced by a different lone element.

  30. More Examples • 3AgCl + Al  AlCl3 +3 Ag • 2Na + H2O  H2 + 2NaOH • Zn3N2 + 3Mg  Mg3N2 + 3Zn

  31. Double Displacementel double • Silver nitrate and sodium chloride react to form silver chloride and sodium nitrate. Write and balance the reaction. • KEY POINT: FIGURE OUT THE FORMULA FOR EACH INORGANIC PIECE AND DON’T MESS WITH THE FORMULA FOR THE REST OF THE TIME!

  32. El Double • AgNO3 + NaCl  AgCl + NaNO3 • It’s already balanced. • The Ag and Na switched places. • That’s why it’s a double displacement.

  33. El Double 2 • Barium nitrate and potassium sulfate reaction to form barium sulfate and potassium nitrate. Write and balance the equation.

  34. Wiki Delay • Due Wednesday of Next week. NO further extensions will be announced. • Homework for chapter 7 is due Monday.

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