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Balancing equations
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Balancing equations



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  • 1. Balancing Equations Just repeat: “I know I can, I know I can!”
  • 2. Balancing equations  Conservation   of Matter: During a chemical reaction, atoms cannot be created or destroyed! Due to the conservation of matter, equations MUST be balanced! Thus, the total number of atoms in the products must equal the total number of atoms in the reactants REMEMBER: The atoms are only being rearranged during the reaction!
  • 3. Coefficients vs. Subscripts  Subscripts tell us how many atoms there are in the molecule. H2O This tells us that there are 2 Hydrogen atoms bonded to one Oxygen atom  Coefficients tell us how many molecules there are. 2 H2O This tells us that there are 2 molecules of H2O
  • 4. Coefficient 2H2O Subscript
  • 5. Use of coefficients in balancing  When balancing a chemical equation, we can ONLY add coefficients!  Coefficients do not change the molecules in the reaction, they merely tell us how many molecules were needed for the reaction to occur.  We cannot add/change subscripts when balancing the equation. Any guesses why???
  • 6. Don’t use subscripts!!!!  Because…..  It changes the actual molecule!!! Which would change either the reactant or the product! Example: H2O is water, but H2O2 is hydrogen peroxide. That is a huge difference! Ok, let’s try balancing some equations together!
  • 7. How to balance an equation  FIRST STEP: Write out the equation with the reactants and products in the formula: MgO + HBr ---> MgBr2 + H2O (Magnesium oxide and Hydrogen Bromide becomes Magnesium Bromide and Water.)
  • 8. How to balance an equation  SECOND STEP: Count the Atoms of each element on both sides of the equation. MgO + HBr ---> MgBr2 + H2O 1 Mg 1O 1H 1 Br 1 Mg 1O 2H 2 Br
  • 9. How to balance an equation  THIRD STEP: Use coefficients to balance the equation MgO + HBr ---> MgBr2 + H2O We need a total of two hydrogen and bromine on the reactants side in order to balance this equation.
  • 10. How to balance an equation  And we’re done! Our balanced equation: MgO + 2HBr ---> MgBr2 + H2O Double check your work, by counting again: 1 Mg 1 Mg 1O 1O 2H 2H 2 Br 2 Br
  • 11. Try one on your own! H + O  H 2O H- 1 O- 1 H- 2 O- 1 2H + O  H2O
  • 12. Let’s do another, for fun!! Fe + HCl ---> FeCl2 +H2 1 Fe 1H 1 Cl 1 Fe 2H 2 Cl Fe + 2HCl ---> FeCl2 +H2
  • 13. Let’s try a couple more… N2 + O2 ---> N2O5 2N 2O 2N 5O We need to balance out the Oxygen first, then the Nitrogen. This gives us… 2N2 + 5O2 ---> 2N2O5 4N 10 O 4N 10 O
  • 14. One More… C2H4 + O2 ---> CO2 + H2O 2C 4H 1C 2H 2O 3O C2H4 + 3O2 ---> 2CO2 + 2H2O