1. Balancing Equations Balancing and writing equations

2. 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. 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. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Balancing Equations

3. Solid (s) Solid (s) Liquid (l) Liquid (l) Gas (g) Gas (g) Aqueous solution (aq) Aqueous solution (aq) Catalyst H 2 SO 4 Catalyst H 2 SO 4 Symbols Used in Equations

4. Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound. The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

5. Chemical Equations 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules ---produces---> 2 molecules of Al 2 O 3 2 molecules of Al 2 O 3 AND/OR AND/OR 4 moles of Al + 3 moles of O 2 ---produces---> 2 moles of Al 2 O 3 2 moles of Al 2 O 3

6. There are four basic steps to balancing a chemical equation. 1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS! 2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side. 3. 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. 4. Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced) The coefficients are in the lowest possible whole number ratios. (reduced) Steps to Balancing Equations

7. Some Suggestions to Help You Some of Mr. Rapp’s 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. 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) 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) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

8. Solid (s) Solid (s) Liquid (l) Liquid (l) Gas (g) Gas (g) Aqueous solution (aq) Aqueous solution (aq) Catalyst H 2 SO 4 Catalyst H 2 SO 4 Symbols Used in Equations

9. Balancing Equations

10. Law of Conservation of Matter: Law of Conservation of Matter: Matter cannot be created nor destroyed, but is only rearranged. Matter cannot be created nor destroyed, but is only rearranged. In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, the amount of reactants must equal the amount of products. In a chemical reaction, the amount of reactants must equal the amount of products.

11. Balancing Equations Paraphrase: Paraphrase: Law of Conservation of Atoms: Law of Conservation of Atoms: The number of atoms of each type of element must be the same on each side of the equation. The number of atoms of each type of element must be the same on each side of the equation.

12. 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. 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. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Balancing Equations

13. Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound. The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

14. Balancing Equations Balancing hints: Balancing hints: Start at the very left-most atom Start at the very left-most atom Save hydrogen to second to last, and then oxygen very last Save hydrogen to second to last, and then oxygen very last Treat polyatomic ions that are present on both sides of the equation as single units. Treat polyatomic ions that are present on both sides of the equation as single units.

15. Chemical Equations 4 Al(s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules ---produces---> 2 molecules of Al 2 O 3 2 molecules of Al 2 O 3

16. There are five basic steps to balancing a chemical equation. 1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS! 2. Record the states of substances (if given). 3. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side. 4. 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. 5. Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced) The coefficients are in the lowest possible whole number ratios. (reduced) Steps to Balancing Equations

17. Balancing Equations Hydrogen and oxygen are diatomic elements. Their subscripts cannot be changed. The subscripts on water cannot be changed. Hydrogen + oxygen water Hydrogen + oxygen water H 2 + O 2 H 2 O H 2 + O 2 H 2 O

18. Balancing Equation Count the atoms on each side. Reactant side: 2 atoms H and 2 atoms O Product side: 2 atoms H and 1 atom O H 2 + O 2 H 2 O H 2 + O 2 H 2 O

19. Balancing Equations H 2 + O 2 H 2 O H 2 + O 2 H 2 O If the subscripts cannot be altered, how can the atoms be made equal? If the subscripts cannot be altered, how can the atoms be made equal? Adjust the number of molecules by changing the coefficients. Adjust the number of molecules by changing the coefficients.

20. Balancing Equations Reactants: 2 atoms of H and 2 atoms of O Products: 4 atoms of H and 2 atoms of O H is no longer balanced! H 2 + O 2 2H 2 O H 2 + O 2 2H 2 O

21. Balancing Equations Reactant side: 4 atoms of H and 2 atoms of O Product side: 4 atoms of H and 2 atoms of O It’s Balanced! 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O

22. Balancing Equations Count atoms. Reactants: 2 atoms N and 2 atoms H Products: 1 atom N and 3 atoms of NH 3 N 2 + H 2 NH 3 N 2 + H 2 NH 3 Nitrogen + hydrogen ammonia Nitrogen + hydrogen ammonia

23. Balancing Equations Nothing is balanced. Nothing is balanced. Balance the nitrogen first by placing a coefficient of 2 in front of the NH 3. Balance the nitrogen first by placing a coefficient of 2 in front of the NH 3. N 2 + H 2 2NH 3 N 2 + H 2 2NH 3

24. Balancing Equations Hydrogen is not balanced. Hydrogen is not balanced. Place a 3 in front of H 2. Place a 3 in front of H 2. Reactant side: 2 atoms N, 6 atoms H Reactant side: 2 atoms N, 6 atoms H Product side: 2 atoms N, 6 atoms H Product side: 2 atoms N, 6 atoms H N 2 + 3H 2 2NH 3 N 2 + 3H 2 2NH 3

25. Balancing Equations Sulfur is not balanced. Sulfur is not balanced. Cu + H 2 SO 4 CuSO 4 + H 2 O + SO 2

26. Balancing Equations Sulfur is not balanced. Sulfur is not balanced. Place a two in front of sulfuric acid. Place a two in front of sulfuric acid. Count atoms: 2 H 2 SO 4 H – 4, S – 2, O - 8 Count atoms: 2 H 2 SO 4 H – 4, S – 2, O - 8 Cu + 2H 2 SO 4 CuSO 4 + H 2 O + SO 2

27. Balancing Equations Hydrogen needs to be balanced so place a 2 in front of the H 2 O. Hydrogen needs to be balanced so place a 2 in front of the H 2 O. Count the number of atoms. Count the number of atoms. Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2

28. Balancing Equations Reactants: Cu – 1, H – 4, S – 2, O – 8 Reactants: Cu – 1, H – 4, S – 2, O – 8 Products: Cu – 1, S – 1, O – 4, H – 4, O – 2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O – 8 Products: Cu – 1, S – 1, O – 4, H – 4, O – 2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O – 8 It’s balanced! It’s balanced! Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2

29. Writing and Naming Write the corresponding formula equation and then balance the equation. Nickel + hydrochloric acid Nickel(II) chloride + hydrogen

30. Writing and Naming Write each formula independently. Write each formula independently. Ignore the rest of the equation. Ignore the rest of the equation. Balance the equation after writing the formulas. Balance the equation after writing the formulas. Ni + HCl NiCl 2 + H 2 Ni + HCl NiCl 2 + H 2 Ni + 2HCl NiCl 2 + H 2 Ni + 2HCl NiCl 2 + H 2