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Unit 7: Chemical Reactions

Unit 7: Chemical Reactions. Balancing Equations Chapter 11.1 Pages 324-329. Balancing Equations. Atom Inventories Writing a correct chemical equation and counting the number of atoms of each element is VERY important Subscripts Indicate the number of ATOMS in a compound

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Unit 7: Chemical Reactions

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  1. Unit 7:Chemical Reactions Balancing Equations Chapter 11.1 Pages 324-329

  2. Balancing Equations • Atom Inventories • Writing a correct chemical equation and counting the number of atoms of each element is VERY important • Subscripts • Indicate the number of ATOMS in a compound • NEVER changed in order to balance an equation – this will change the substance itself

  3. Balancing Equations • Atom Inventories • Writing a correct chemical equation and counting the number of atoms of each element is VERY important • Coefficients • Indicate the number of ELEMENTS or COMPOUNDS in a reaction • CAN be changed to balance an equation • Determines the molar ratio of substances in a reaction

  4. Balancing Equations • Atom Inventories • Practice • C6H12O6 • Ca(OH)2 • 3H2O2 • 2Fe2(CO3)3 • 3CaNO3 + 2O2 C = 6; H = 12; O = 6 Ca = 1; O = 2; H = 2 H = 6; O = 6 Fe = 4; C = 6; O = 18 Ca = 3; N = 3; O = 13

  5. Balancing Equations • Keeping Track of Atoms Activity • Work in groups of three and finish this activity in the next 10 minutes • Your group may ask me a total of two questions during this time…use them wisely • To get credit for this activity, ALL group members must have their sheet checked and 100% correct by the end of the time • Begin now….

  6. Balancing Equations • Keeping Track of Atoms Activity 14 minutes 10 minutes 4 minutes 2 minute Time’s Up!! 20 minutes 6 minutes 16 minutes 8 minutes 18 minutes 12 minutes

  7. Balancing Equations • Balanced Equations • A chemical equation that shows the same number of atoms of each element on each side of the equation. • Based on the Law of Conservation of Matter • Matter cannot be created or destroyed, only changed

  8. Balancing Equations • Balance Equations • Number of atoms on the reactant side must equal the number of atoms on the product side • C + O2 CO2 C C O O O O

  9. Balancing Equations • Balance Equations • Number of atoms on the reactant side must equal the number of atoms on the product side • Cu + O2 CuO • Not balanced! Add coefficients • 2Cu + O2 2CuO Cu O Cu Cu O O Cu O

  10. Balancing Equations • Balancing Equations • Steps 1) Determine the correct chemical formulas for each substance. 2) Write the skeleton (unbalanced) equation. 3) Do an atom inventory (count the number of atoms on each side). *Count polyatomic ions as one atom

  11. Balancing Equations • Balancing Equations • Steps 4) Use coefficients to get the number of atoms to equal on each side of the equation. 5) Redo the atom inventory with the new coefficients. 6) Make sure coefficients are in the lowest whole number ratio.

  12. Balancing Equations • Examples…balance skeleton equations from the Chemical Reactions homework #6-10

  13. Balancing Equations • Algebraic Balancing 1) Assign letters to unknown coefficients. 2) Make a grid indicating the appearance of an element in each substance of the equation. Use a whole number and the coefficient “letter” to indicate each appearance.

  14. Balancing Equations • Algebraic Balancing 3) Reduce each equation. 4) Assume a=1. 5) Solve for the coefficients. If there is a fraction for a coefficient, multiply ALL coefficients by the denominator. 6) Write the balanced equation.

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