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7.4: Balancing Chemical Equations

7.4: Balancing Chemical Equations. By Lexy O’Neill and Joanna Au. What is a balanced equation?. Both sides of the equation contains the same number of atoms of each element. It is necessary to balance the equation in order to be consistent with the law of conservation of mass.

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7.4: Balancing Chemical Equations

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  1. 7.4: Balancing Chemical Equations By Lexy O’Neill and Joanna Au

  2. What is a balanced equation? • Both sides of the equation contains the same number of atoms of each element. • It is necessary to balance the equation in order to be consistent with the law of conservation of mass.

  3. BALANCED AND UNBALANCED EQUATIONS balanced equations unbalanced equations Use coefficients to balance the equation No need for coefficients because same number on each side

  4. Rules for Balancing Equations: What to write down to get started • Identify the formulas for all the reactants and products. Make sure they are the correct ones. • On the left, write the formulas of the reactants. Write a yields sign (→). On the right, write the formulas of the products. Separate formulas with plus signs if there are two or more reactants or products used.

  5. Rules for Balancing Equations: How to balance it • Count how many atoms of each element are in the reactants and products; make note of it. If there is a polyatomic ion that remains the same on both sides of the equation, note it as a single unit. • Balance each element one at a time with coefficients because the coefficients will even out the amount of atoms of each element on either side. coefficient – a small whole number in front of a chemical formula in the equation Begin with elements that appear only once on either side of the equation. Do not change the subscripts in the chemical formula to balance the equation.

  6. Rules for Balancing Equations:Checking your work • Check the number of each atom or polyatomic ion there is and make sure each side of the equation has the same number so the equation is balanced. • Make sure all coefficients are in the lowest possible ratio.

  7. Example Balance this equation: Al + O2 → Al2O3 Al: 1atom Al: 2 atoms O: 2 atoms O: 3 atoms 2Al + O2 → Al2O3 2Al + O2 → 2Al2O3 Al: 2 atoms Al: 2 atoms Al: 2 atoms Al: 4 atoms O: 2 atoms O: 3 atoms O: 2 atoms O: 6 atoms 4Al+ O2 → 2Al2O3 4Al + 3O2 → 2Al2O3 Al: 4 atoms Al: 4 atoms Al: 4 atoms Al: 4 atoms O: 2 atoms O: 6 atoms O: 6 atoms O: 6 atoms Answer: 4Al + 3O2 → 2Al2O3

  8. Now You Try! Balance this equation: H2 + O2→ H2O • H2 + O2→ 2H2O • 2H2 + O2→ H2O • 2H2 + 2O2 → 2H2O • 2H2 + O2→ 2H2O

  9. Up for a challenge? Balance this equation: AgNO3 + Cu → Cu(NO3)2 + Ag • 2AgNO3 + Cu → Cu(NO3)2 + Ag • 2AgNO3 + Cu → Cu(NO3)2 + 2Ag • AgNO6 + Cu → Cu(NO3)2 + Ag • 4AgNO3 + 2Cu → 2Cu(NO3)2+ 4Ag

  10. History of Balancing Chemical Equations • Roman poet Lucretius stated, “Things cannot be born from nothing.” He set a foundation for future scientists to work off of, leading to Antoine Laviosier founding the concept of balancing chemical equations. • Antoine Laviosier would not accept what everyone said about how an object could have a positive, negative, or no weight so he proved that the metal combining with air caused the weight to increase. They had to balance the equation in order to have the mass of the products equivalent to the mass of the reactants because of the law of conservation of mass.

  11. HOMEWORK QUESTION Balance this equation: Fe + Cl2 → FeCl3

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