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Balancing Chemical Equations

Balancing Chemical Equations. Parts of a Chemical Equation. Chemical reactions continued . Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken What do we call those “outermost parts”??? Valence electrons.

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Balancing Chemical Equations

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  1. Balancing Chemical Equations

  2. Parts of a Chemical Equation

  3. Chemical reactions continued • Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken • What do we call those “outermost parts”??? • Valence electrons

  4. Symbols represent elementsFormulas represent the moleculesChemical equations represent the reaction

  5. Law of conservation of matter “mass is neither created nor destroyed in any ordinary chemical reaction. “ • Or more simply, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).

  6. Law of conservation of matter • Ex’s • 1.00g carbon + 5.34g sulfur  _____g carbon disulfide? • 6.34g carbon disulphide • 2.00g carbon + 10.68g sulfur  _____g carbon disulfide? • 12.68g carbon disulphide

  7. Balancing Equations • To follow the law of conservation of mass, any equation must be BALANCED • (Mass of reactants must equal the mass of the products)

  8. BALANCING EQUATIONS • When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the … • subscripts. • Changing the subscripts changes the compound. • H2O is very different that H2O2 • (Water vs Hydrogen Peroxide!)

  9. Subscripts tell you how many atoms of each element you haveCoefficients tell you how many of each molecule you have

  10. Ex: 4 Al + 3 O2 2Al2O3 This equation means : “4 Al atoms + 3 O2 molecules produces 2 molecules of Al2O3”

  11. Steps to Balancing Chemical Equations • 1. Write out the equation leaving room to add coefficients. • Ex- Na3PO4 + Fe2O3 Na2O + FePO4

  12. Step 2: Record how many atoms of each element 2. Find the number of atoms for each element on each side. • YOU MUST COMBINE ALL of the same element together… • ex Na3PO4 + Fe2O3 Na2O _ FePO4 • Na- 3 Na-2 • P-1 P-1 • Fe- 2 Fe- 1 • O- 7 O-5 HINT- write them in the same order on both sides so that it is easier to compare them

  13. STEP THREE Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.

  14. 2 Na3PO4 +___ Fe2O3 3 Na2O + 2 FePO4 • Na- 3 6Na-2 6 • P-1 2P-1 2 • Fe- 2 Fe- 1 2 • O- 7 11O-5 9 11

  15. Step 4… 4. Check your answer to see if: • The numbers of atoms on both sides of the equation are now balanced. • The coefficients are in the lowest possible whole number ratios. (reduced)

  16. Some Helpful Hints for balancing equations: • Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last. • IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element)

  17. Example Illustration:

  18. Let’s try a few 1. ___ C3H8 + ___ O2  ____ CO2 + ___ H2O

  19. Ready for another? 2. _____B4H10 +___O2___B2O3 + ____H2O

  20. One more… 3. __Na3PO4 + ___ Fe2O3  __Na2O + __ FePO4

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