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Chemical Equations Review

Chemical Equations Review. CH 4 + 2 O 2 CO 2 + 2 H 2 O “ coefficients ” “ subscripts ” coefficients can be changed to achieve mass balance but subscripts are never changed to balance an equation Why?

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Chemical Equations Review

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  1. Chemical Equations Review CH4 + 2O2 CO2 + 2H2O “coefficients” “subscripts” coefficientscan be changed to achieve mass balance but subscripts are never changed to balance an equation Why? Because changing a subscript changes the compound entirely!!!

  2. So how do we get subscripts? In ionic compounds you simply cross the ions charge values. Li + MgCl2 ??????? Single replacement reaction. Why? Li is a metal, Mg is a metal, Cl is a nonmetal Li+ replaces Mg2+ and combines with Cl- The products are Mg + LiCl The balanced equation will be 2 Li + MgCl2 Mg + 2 LiCl

  3. Balancing a Chemical Equation • write formula for each reactant and product on the correct side of the “reaction arrow” • count atoms of each element on both sides of arrow • start with the compound which has the most complex formula • add coefficients to chemical formulas to balance numbers of each atom • trial and error begins...

  4. What am I? Mg + HCl  MgCl2 + H2 Single replacement Na2CO3 + HCl  NaCl + H2CO3 Double replacement Cu + S Cu2S Synthesis

  5. NaCl is soluble in water. Solid NaCl dissociates into Na+ and Cl- ions in aqueous solution: NaCl(s) Na+(aq) + Cl-(aq)

  6. Pb(NO3)2 + 2NaI  PbI2 + 2NaNO3 (aq) (aq) (s) (aq) See solubility rules

  7. Solubility Rules:

  8. Net Ionic Equations Balanced Chemical Equation: Pb(NO3)2(aq) + 2NaI(aq)  PbI2(s) + 2NaNO3(aq) “Complete Ionic” Equation: Pb2+(aq) + 2NO3-(aq) + 2Na+(aq)+ 2I-(aq)  PbI2(s) + 2Na+(aq) + 2NO3-(aq) Cancel the “spectator ions” that appear on both sides of the arrow Pb2+(aq) + 2NO3-(aq) + 2Na+(aq)+ 2I-(aq)  PbI2(s) + 2Na+(aq) + 2NO3-(aq) “Net Ionic” Equation: Pb2+(aq) + 2I-(aq)  PbI2(s)

  9. For the exam: know how to use solubility rules to predict whether an ionic compound is insoluble or not

  10. Net Ionic Equations Revisited: • Write the (balanced!) molecular equation first • Reaction products: swap cations and anions • Predict solubility (using Solubility rules) • Write the complete ionic equation next • (s) compounds don’t ionize • (aq) compounds do ionize • ion subscripts in the molecular equation become coefficients in the complete ionic equation! • Write the netionic equation next • cancel spectator ions • The net ionic equation is a “simplified” form • of the complete ionic equation

  11. Example: Problem Ba(NO3)2 + NiSO4 Balanced Molecular Equation:

  12. Example: Problem Ba(NO3)2 + NiSO4 Ni(NO3)2 + BaSO4 Balanced Molecular Equation:

  13. Example: Problem Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2(aq)+ BaSO4(s) Balanced Molecular Equation:

  14. Example: Problem Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2(aq)+ BaSO4(s) Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) +SO42-(aq) Ni2+(aq) + 2NO3-(aq) + BaSO4 (s) Balanced Molecular Equation: Complete Ionic Equation:

  15. Example: Problem Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2(aq)+ BaSO4(s) Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) +SO42-(aq) Ni2+(aq) + 2NO3-(aq) + BaSO4 (s) Balanced Molecular Equation: Complete Ionic Equation:

  16. Example: Problem Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2(aq)+ BaSO4(s) Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) +SO42-(aq) Ni2+(aq) + 2NO3-(aq) + BaSO4 (s) Balanced Molecular Equation: Complete Ionic Equation: Net Ionic Equation: Ba2+(aq) + SO42-(aq) BaSO4 (s)

  17. What is the Net Ionic Equation for the reaction: HCl(aq) + NaOH(aq) ?

  18. HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) H+(aq) + -OH(aq) H2O(l)

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