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Chemical Reactions

Chemical Reactions. Writing Formulas: Review. carbon tetrafluoride. CF 4. prefixes  covalent  prefixes indicate subscripts. Na 3 PO 4. sodium phosphate. metal  ionic  balance charges  3 Na 1+ needed for 1 PO 4 3-. cuprous sulfate. Cu 2 SO 4.

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Chemical Reactions

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  1. Chemical Reactions

  2. Writing Formulas: Review carbon tetrafluoride CF4 prefixes  covalent  prefixes indicate subscripts Na3PO4 sodium phosphate metal  ionic  balance charges  3 Na1+ needed for 1 PO43- cuprous sulfate Cu2SO4 metal present  ionic  balance charges 2 Cu1+ needed for 1 SO42- aluminum sulfide Al2S3 metal present  ionic  balance charges 2 Al3+ needed for 3 S2- dinitrogen pentoxide N2O5 prefixes  covalent  prefixes indicate subscripts ammonium nitrate NH4NO3 polyatomic ion present  ionic  balance charges  1 NH41+ needed for 1 NO31- plumbic oxide PbO2 metal present  ionic  balance charges 1 Pb4+ needed for 2 O2- ferric carbonate Fe2(CO3)3 metal present  ionic  balance charges 2 Fe3+ needed for 3 CO32-

  3. Indicators of a Chemical Change • Precipitate • Color Change • Gas Given off • Temperature Change • Light Produced

  4. Reactants vs. Products • In a chemical reaction, reactants are chemically combined or broken down to make (produce) products. • arrow always points toward products! CH4(g) + 2O2(g) CO2(g) + 2H2O(l) yields products reactants

  5. - a whole number that is placed before a symbol of an element or formula of a compound in order to balance a chemical equation. A coefficient multiplies the entire formula by that whole number. Example - 2 Al + 6 HCl 2AlCl3 + 3 H2 2 Al 2Al 6H  6H 6Cl  6Cl Coefficient

  6. - there are seven elements that exist as diatomic molecules in which two atoms of the same element bond together. Br I N Cl H O F Whenever these elements appear as free elements (by themselves) in a chemical equation, they MUST have a subscript "2" written beside them. Example 1 - 2 H2 + O22H2O Example 2 - 2 Na + Cl2 2NaCl Example 3 - 3 H2 + N2 2NH3 Diatomic Elements

  7. Sometimes chemical equations are written using the names of the free elements and compounds. But, usually chemical equations are written with symbols for free elements and formulas for compounds instead of names. Examples: magnesium + hydrochloric acid  magnesium chloride + hydrogen Mg + 2 HCl  MgCl2 + H2 sodium + water  sodium hydroxide + hydrogen 2Na+ 2H2O  2 NaOH + H2 Writing Chemical Equations

  8. Types of Reactions • There are five different types of reactions… • 1. SYNTHESIS or COMBINATION… - two or more reactants combine to produce one product. • Ex… 2 2 Mg (s) + O2 (g) MgO (s) 2:1 2 CaO (s) + CO2 (g) CaCO3(s) 1:1 1 2 2 KNO2 (s) + O2 (g) KNO3(s) 2:1 2

  9. Types of Reactions • 2. DECOMPOSITION… - opposite of synthesis - A single compound (one) reactant breaks down (decomposes) into two or more elements or new compounds (products). • Ex… 2 2 HgO Hg + O2 2 2:1 2 HNO3 N2O5 +H2O 2 1:1

  10. Types of Reactions • 3. SINGLE DISPLACEMENT… - one element in a compound is displaced (kicked out) by another (more reactive) element. - reactants =1element &1compound …products = 1element & 1compound. -By definition, all single replacement reactions are redox reactions • Ex… Mg + Zn(NO3)2 Mg(NO3)2 + Zn 1:1 1:1 2 2 Cl2 + KI KCl + I2 1:2 2:1 ** metals can only replace metals and vice versa for non-metals!

  11. Types of Reactions • 4. DOUBLE DISPLACEMENT… - cations of two different compounds trade places. - reactants = 2 compounds …products = 2 different compounds • Ex… NaCl + AgNO3 AgCl + NaNO3 1:1 1:1 2 3 Ca(OH)2 + H3PO4 6 H(OH) + Ca3(PO4)2 (H2O) 3:2 6:1

  12. Types of Reactions • 5. COMBUSTION… - oxygen combines with a substance and releases energy in the form of heat and light. - generally involves the burning of a hydrocarbon. - fires generally need oxygen to burn (reactant). - fires generally release water and carbon dioxide (prod). - reactants = hydrocarbon and O2 …products = H2O and CO2 • Ex… 4 3 5 C3H8 + O2 CO2 + H2O 1:5 3:4 6 6 6 C6H12O6 + O2 CO2 + H2O 1:6 6:6

  13. Types of Reactions • identify the following types of rxns… Pb(NO3)2 + K2CrO4 PbCrO4 + 2KNO3 double displacement 2Al(OH)3 Al2O3 + 3H2O decomposition CH4 + 2O2 CO2 + 2H2O combustion 2Li2O synthesis 4Li + O2 2Al + 3CuSO4 Al2(SO4)3 + 3Cu single displacement

  14. Balancing Chemical Equations

  15. Balancing Equations • chemical equations need to be balanced to comply w/ the Law of Conservation of Mass. (matter cannot be created or destroyed) • # of atoms for each element must = each other on both sides of rxn. ** use coefficients to balance. - large # in front of compound - must be whole #s - indicate the mole ratio each time you balance! • start from far left and work your way to the right!

  16. Balancing Equations • Practice… 2 2 O2 (g) + H2 (g) H2O (l) 4 H atoms 1 O atom 2 O atoms Mole Ratio = 1:2 2 3 2 4 2 Fe (s) + O2 (g) Fe2O3(s) Mole Ratio = 4:3 2

  17. Balancing Equations • Practice… 2 H2O2 (aq) O2 (g) + H2O (l) 2 Mole Ratio = 2 1:2 2 2 AgNO3 + H2S Ag2S + HNO3 Mole Ratio = 2:1 1:2 ** balance polyatomics together! 4 2 MnO2 + HCl MnCl2 + H2O + Cl2 Mole Ratio = 1:4 1:2:1

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