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Chemical Equations Unit 3 Module 1

Chemical Equations Unit 3 Module 1. Counting Atoms Review. Co-efficient The large number in front of a compound representing the number of units taking part in the reaction Subscript Tells how many atoms are in each molecule Subscripts counted for that element only

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Chemical Equations Unit 3 Module 1

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  1. Chemical Equations Unit 3 Module 1

  2. Counting Atoms Review • Co-efficient • The large number in front of a compound representing the number of units taking part in the reaction • Subscript • Tells how many atoms are in each molecule • Subscripts counted for that element only • H2O = 2 ATOMS of HYDROGEN

  3. Counting Atoms Review • Coefficients counted for every element in the compound • 2 H2O • H = 4 • O = 2 • 4Al2(SO4)3 • Aluminum: 2 * 4 = 8 • Sulfur: 1*3 = 3 * 4 = 12 • Oxygen: 4 * 3 = 12 * 4 = 48

  4. Chemical Reactions • When bonds are broken and new bonds are formed • Energy is released from the old bonds and stored in the new bonds • New combination of elements • Chemical properties in new substances are different from the properties of the old substances

  5. Evidence of Chemical Reactions • A gas is formed (Bubbles) • A Precipitate is formed (Turns cloudy because a new solid forms) • There is a energy / temperature change (Because bonds are breaking and re-forming) • There is a color change (Because new substances are forming • Light is produced

  6. Chemical Equations • An expression that describes a chemical reaction 2Mg + O2 2MgO

  7. Chemical Equation Language REACTANTS PRODUCTS 2Mg + O2 2MgO • Reactants • On the left of the arrow • The elements/compounds you start with • 2Mg + O2 • Products • On the right of the arrow • The elements/ compounds you finish with • 2MgO

  8. Chemical Equation Language REACTANTS PRODUCTS • Arrow • “Yields” or “Results in” • Separates the reactants from the products

  9. Chemical Equation Language 3Fe(s) + 4H2O(l) 1Fe3O4(aq) + 4H2(g) • (s) • This Reactant is in SOLID form • (l) • This Reactant is in LIQUID form • (aq) • This Product is in AQUEOUS form (Mixed with Water) • (g) • This Product is in GAS form

  10. Practice: Counting Atoms • Fe(SO4) • Fe = • S = • O = • 4Cu(SO4) • Cu = • S = • O = • 6Zn(NO3)2 • Zn = • N = • O =

  11. Practice: Equations ZnBr2 + 2Ag(NO3) Zn(NO3)2 + 2AgBr • What are the reactants? • What are the products? • How many molecules are there of AgBr? • How many atoms of Oxygen are there in Ag(NO3)?

  12. Law of Conservation of Mass • Mass (matter) can be neither created or destroyed • It just changes from one form to another • Example: BURNED WOOD 500g Wood 300g Ash + 200g Smoke • Reactant: 500g Wood • Product: 300g Ash + 200g Smoke • TOTAL MASS OF THE PRODUCTS OF A REACTION IS EQUAL TO THE TOTAL MASS OF THE REACTANTS.

  13. Law of Conservation of Mass 2KClO3 2KCl + 3O2 • If 500 grams of KClO3 decomposes (breakdowns) and produces 303 grams of KCl, how many grams of O2 are produced? 500 grams 303 grams + ? 500 grams 303 grams + 197 grams

  14. Law of Conservation of Mass 2KI + Pb(NO3)2 PbI2 + K(NO3) • If 700 grams of the product is produced, how many grams of KI do you start with if you also have 520 grams of Pb(NO3)2? 520 grams + ? 700 grams 520 grams + 180 grams 700 grams

  15. Law of Conservation of Mass 2H2S + O2 H2O + S • If you have 250 grams of water and 380 grams of sulfur, how many grams of oxygen do you have if you start with 400 grams of H2S? ? + 400g 250g + 380g ? + 400g 630g 230g + 400g 630g

  16. Balanced Chemical Equations • Shows Chemical Reactions in a Conservation of Mass form • The total mass of the reactants MUST equal the total mass of the products • A BALANCED EQUATION has the same ELEMENTS & the same # OF ATOMS in BOTH the reactants and products

  17. Balancing Chemical Equations • IN A CHEMICAL EQUATION, THE # & TYPE OF ATOMS ON BOTH SIDES MUST BE EQUAL!! • THIS IS NOT BALANCED!!!! H2 + O2 H2O H = 2 H = 2 O = 2 O = 1

  18. Balancing Chemical Equations • ONLY CO-EFFICIENTS MAY BE CHANGED OR ADDED TO BALANCE AN EQUATION!!! • THE NUMBER BEFORE THE COMPOUND • SUBSCRIPTS MAY NOT BE CHANGED OR ADDED!!!!! • THE SMALL NUMBER AFTER THE COMPOUND 2H2 + O22H2O BALANCED

  19. How to Balance • Write the equation with boxes in front of each compound H2 + O2 H2O • Count the # of atoms of each element in the reactants and the products H = 2 H = 2 O = 2 O = 1 • If any numbers are different, the equation is NOT balanced

  20. How to Balance • Change ONLY the coefficients to balance the equation H2 + O22 H2O H = 2 H = 2 4 O = 2 O = 1 2 • The equation is BALANCED when the same number of atoms of each element are on BOTH sides of the equation 2 H2 + 1 O22 H2O H = 2 4 H = 4 O = 2 2O = 2

  21. LET’S PRACTICE!!! • __CH4 +__ O2 __CO2 + __H2O • __Al +__Br2 __AlBr3

  22. LET’S PRACTICE!!! • 1 CH4 + 2 O2 1CO2 + 2 H2O • 2 Al + 3 Br2 2 AlBr3

  23. LET’S PRACTICE!!! • _SrCl2 +_KNO3 __ Sr(NO3)2+_KCl • __KOH +__H2SO4 __K2SO4 +__H2O

  24. LET’S PRACTICE!!! • 1 SrCl2 +2 KNO31 Sr(NO3)2+2 KCl • 2 KOH +1 H2SO41 K2SO4 +2 H2O

  25. LET’S PRACTICE!!! • __H2O +__N2O3 __HNO2 • __Fe +__H2O __Fe3O4 + __H2

  26. LET’S PRACTICE!!! • 1 H2O +1 N2O32 HNO2 • 3 Fe + 4 H2O 1 Fe3O4 + 4 H2

  27. LET’S PRACTICE!!! • __C12H22O11 + __H2O __C + __H2O • __Na2(SO4) +__BaCl2 __BaSO4+__NaCl

  28. LET’S PRACTICE!!! • 1 C12H22O11 + 1 H2O 12 C + 12 H2O • 1 Na2(SO4) + 1 BaCl21 BaSO4+ 2 NaCl

  29. LET’S PRACTICE!!! • __PbO2 __PbO + __O2 • __Cl2 +__KBr __KCl +__Br2

  30. LET’S PRACTICE!!! • 2 PbO22 PbO + 1 O2 • 1 Cl2 +2 KBr 2 KCl + 1 Br2

  31. LET’S PRACTICE!!! • __NaCl + __H2(SO4) __Na2SO4 +__HCl

  32. LET’S PRACTICE!!! • 2 NaCl + 1 H2(SO4) 1 Na2SO4 + 2 HCl

  33. Ratios & Chemical Equations • Ratios are written #:#:# • Use the Co-efficients when writing ratios 2 H2 + 1 O2 2 H2O RATIO FOR THIS EQUATION = 2:1:2

  34. QUESTION: • If I have 10 molecules of O2, how many molecules of H2O do I have? 2 H2 + 1 O2 2 H2O RATIO FOR THIS EQUATION = 2:1:2

  35. ANSWER: • If I have 10 molecules of O2, how many molecules of H2O do I have? 2 H2 + 1 O2 2 H2O RATIO FOR THIS EQUATION = 2 : 1 : 2 Oxygen Coefficient = 10/1 = 10 molecules Water Coefficient = 2*10 = 20 Molecules

  36. QUESTION: • If I have 30 molecules of H2O, how many molecules of O2 do I have? 2 H2 + 1 O2 2 H2O RATIO FOR THIS EQUATION = 2:1:2

  37. ANSWER: • If I have 30 molecules of H2O, how many molecules of O2 do I have? 2 H2 + 1 O2 2 H2O RATIO FOR THIS EQUATION = 2 : 1 : 2 Water = 30 molecules/2 = 15 Oxygen = 1*15 = 15 Molecules

  38. QUESTION: • If I have 24 molecules of PbO, how many molecules of Pb do I have? PbS + 2 PbO 3 Pb + SO2 RATIO FOR THIS EQUATION = __ : __ : __ : __

  39. ANSWER: • If I have 24 molecules of PbO, how many molecules of Pb do I have? PbS + 2 PbO 3 Pb + SO2 RATIO FOR THIS EQUATION = 1 : 2 : 3 : 1 PbO = 24 molecules/2 = 12 Pb = 3*12 = 36 Molecules

  40. End notes for Thursday, November 2, 2006

  41. Types of Chemical Reactions • Synthesis Reaction • Decomposition Reaction • Single Displacement Reaction • Double Displacement Reaction • Combustion Reaction

  42. Synthesis Reactions • Addition reaction • Two or more substances chemically combine to form ONE product A + B C 4Al + 3O2 2Al2O3 4Fe + 3O2 2Fe2O3

  43. Decomposition Reactions • Breakdown Reaction • ONE reactant breaks down into two or more substances AB A + B 2KClO3 2KCl + 3O2 2NaH(CO3) 2Na(CO3) + H2

  44. Single Displacement Reactions • One ELEMENT replaces another in a compound A + BC AC + B Ca + 2Ag(NO3) 2Ag + Ca(NO3)2 Fe + CuCl2 FeCl2 + Cu

  45. Double Displacement Reactions • The CATION of one compound replaces the CATION of another compound • TWO compounds produce two NEW COMPOUNDS • Usually produces a PRECIPITATE (something not soluble in water) & a liquid/gas AB + CD AD + CB HCl + NaF HF + NaCl NaCl + KBr NaBr + KCl

  46. Combustion Reactions • A CARBON compound combines with OXYGEN to form CARBON DIOXIDE and WATER CARBON COMPOUND + O2 CO2 + H2O CH4 + 2O2 2H2O + CO2

  47. Energy in Reactions • Energy is released or absorbed in ALL chemical reactions • When bonds are FORMED, energy is RELEASED • When bonds are BROKEN, energy is ABSORBED (Taken In)

  48. Exothermic Reactions • Energy is RELEASED • Usually occurs in the form of HEAT because BONDS ARE BROKEN • More bonds are FORMED than broken

  49. Exothermic Reactions • Energy will be on the PRODUCT side of the chemical equation • Temperature Rises (Feels Warmer) • Examples: • Burning of Gasoline • Heat Packs • Explosion of Dynamite

  50. Endothermic Reactions • Energy is ABSORBED (Taken in) • More bonds are BROKEN than formed • Temperature Drops (Feels Cold) • Energy is on the REACTANT side of the chemical equation • Examples: • Ice pack

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