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UNIT 2 – CHEMICAL REACTIONS

UNIT 2 – CHEMICAL REACTIONS. SCIENCE 1206. OUTLINE. Law of Conservation of Mass Balancing Chemical Reactions Types of Chemical Reactions Simple Composition Simple Decomposition Single Replacement Double Replacement Hydrocarbon Combustion Predicting Reaction Types.

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UNIT 2 – CHEMICAL REACTIONS

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  1. UNIT 2 – CHEMICAL REACTIONS SCIENCE 1206

  2. OUTLINE • Law of Conservation of Mass • Balancing Chemical Reactions • Types of Chemical Reactions • Simple Composition • Simple Decomposition • Single Replacement • Double Replacement • Hydrocarbon Combustion • Predicting Reaction Types

  3. LAW OF CONSERVATION OF MASS

  4. LAW OF CONSERVATION OF MASS • Mass CANNOT be created nor destroyed. • As applied to a chemical reaction, the MASS of the REACTANTS EQUALS the MASS of the PRODUCTS

  5. BALANCED CHEMICAL EQUATIONS • Balanced chemical equations are a means of representing the process in a chemical reaction, whereby REACTANTS form PRODUCTS, as per the Law of Conservation of Mass. • REACTANTS: STARTING MATERIALS • PRODUCTS: NEW MATERIALS • ARROW: “Goes to Form” or “Yields” • COEFFICIENTS: # in front of FORMULA • EXAMPLE: • Iron + oxygen  iron (III) oxide • 4 Fe(s) + 3 O2(g)  2 Fe2O3(s)

  6. BALANCED CHEMICAL EQUATIONS • Make a LIST of atoms for REACTANTS and PRODUCTS. • Count up the NUMBER OF ATOMS on each side. • ADD coefficients in front of the chemical formulae until you have equal numbers on each side. • POINTS TO REMEMBER: • Start with atom that appears in only 1 formula on each side first. • Lowest Common Multiple Rule for coefficients • Keep polyatomic ions together.

  7. TYPES OF CHEMICAL REACTIONS • SIMPLE COMPOSITION/SYNTHESIS (SC): • ELEMENT + ELEMENT  COMPOUND • SIMPLE DECOMPOSITION (SD): • COMPOUND  ELEMENT + ELEMENT • SINGLE REPLACEMENT (SR): • ELEMENT + COMPOUND  ELEMENT + COMPOUND • DOUBLE REPLACEMENT (DR): • COMPOUND + COMPOUND  COMPOUND + COMPOUND • HYDROCARBON COMBUSTION (HC): • CxHy + O2 CO2 + H2O • NEUTRALIZATION: • ACID + BASE  SALT + WATER

  8. CHEMICAL REACTIONS • When studying our chemical reactions, we will use the analogy of RELATIONSHIPS and DANCING!!! • CATIONS will be FEMALES • (remember, they’re positive ions  ) • ANIONS will be MALES • (remember, they’re negative ions  )

  9. SIMPLE COMPOSITION REACTIONS • GENERAL EQUATION: • Element + Element  Compound • ANALOGY: RELATIONSHIP • Amy + Bob  Amy-Bob • A + B  A-B • EXAMPLES: • 4 Fe + 3 O2  2 Fe2O3 • 2 Na + Cl2  2 NaCl

  10. SIMPLE COMPOSITION . . . • PREDICT THE PRODUCTS: • _____ Li + _____ Cl2 • _____ Mg + _____ N2 

  11. SIMPLE DECOMPOSITION REACTIONS • GENERAL EQUATION: • Compound  Element + Element • ANALOGY: BREAKUP • Amy-Bob  Amy + Bob • A-B  A + B • EXAMPLES: • 8 FeS  8 Fe + S8 • 2 H2O  2 H2 + O2

  12. SIMPLE DECOMPOSITION . . . • PREDICT THE PRODUCTS: • _____ NO2 • _____ Mg3P2 

  13. SINGLE REPLACEMENT REACTIONS NEW! NEW! • GENERAL EQUATION: • Element + Compound  Element + Compound • ANALOGY: CHEATING!!! • Amy-Bob + Cherise  Amy + Cherise-Bob • Why, Bob, Why?  • A-B + C  A + C-B • EXAMPLES: • 1 K + 1 NaCl  1 Na + 1 KCl • 1 Cu + 2 AgNO3  2 Ag + 1 Cu(NO3)2

  14. SINGLE REPLACEMENT • PREDICT THE PRODUCTS: • _____ ZnS + _____ O2 • _____ Br2 + _____ NaI 

  15. SINGLE REPLACEMENT . . . • WHAT’S WRONG WITH THE FOLLOWING EQUATION? • 2 NaI + 1 Br2  2 Na + 2 IBr • There are 2 NEGATIVE IONS put together on the PRODUCT SIDE. • IONIC COMPOUNDS are made up of a CATION and an ANION. • CORRECT EQUATION: • 2 NaI + 1 Br2  2 NaBr + 1 I2

  16. DOUBLE REPLACEMENT REACTIONS NEW! NEW! • GENERAL EQUATION: • Compound + Compound  Compound + Compound • ANALOGY: Switching Dance Partners • Amy-Bob + Cherise-Dan  Amy-Dan + Cherise-Bob • A-B + C-D  A-D + C-B • EXAMPLES: • 2 NaCl + 1 MgS  1 Na2S + 1 MgCl2 • 2 AgNO3 + 1 H2SO4  1 Ag2SO4 + 2 HNO3

  17. DOUBLE REPLACEMENT • PREDICT THE PRODUCTS: • ____ Al(NO3)3 + ____ H2SO4  • ____ Pb(NO3)2 + ____ CaSO4 

  18. DOUBLE REPLACEMENT . . . • WHAT’S WRONG WITH THE FOLLOWING EQUATION? • 1 Ca(OH)2 + 1 MgCl2  1 CaMg + 2 ClOH • There are 2 NEGATIVE IONS and 2 POSITIVE IONS put together on the PRODUCT SIDE. • IONIC COMPOUNDS are made up of a CATION and an ANION. • CORRECT EQUATION: • 1 Ca(OH)2 + 1 MgCl2  1 CaCl2 + 1 Mg(OH)2

  19. HYDROCARBON COMBUSTION • GENERAL EQUATION: • CxHy + O2 CO2 + H2O • FOR TRICKY BALANCING, TRY THIS: • Divide the SUBSCRIPT of the H in CxHy by 2. • If your answer is: • EVEN  BALANCE using C-H-O • ODD  Add a “2” coefficient to the CxHy and THEN BALANCE using C-H-O

  20. HYDROCARBON COMBUSTION • PREDICT THE PRODUCTS: • ____CH4 + ____O2 ____CO2 + ____ H2O • ____ C2H6 + ____O2 ____CO2 + ____ H2O • ____ C5H12 + ____O2 ____CO2 + ____ H2O

  21. NEUTRALIZATION • GENERAL EQUATION: • ACID + BASE  SALT + WATER • Also considered a DOUBLE REPLACEMENT REACTION

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