1. Chapter 9 Balancing Equations Part 1

2. Terms A chemical reaction is a process that always results in the change of chemical substances. A chemical equation is a means of writing out a chemical reaction. A reactant or reagent is a substance consumed during a chemical reaction. A product is a substance that forms during chemical reaction.

3. Potassium metal is added to water.

4. K + H 2 O

5. Water can also be written HOH

6. K + HOH

7. What are the products?

8. What gas might be produced?

9. What has happened to the liquid?

10. The litmus test Blue litmus paper turns red under acidic conditions. Red litmus paper turns blue under basic conditions. If both litmus tests result in no change then the solution is neutral.

11. The resulting liquid is a base. Most common bases contain hydroxide (OHˉ).

12. What are the products?

13. K + H 2 O → KOH + H → + What is wrong here?

14. K + H 2 O → KOH + H → + HONClFIBr mean H should be H 2

15. K + H 2 O → KOH + H → + HONClFIBr mean H should be H 2 2

16. K + H 2 O → KOH + H 2 → + Now what is wrong?

17. Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number and type of atoms on both sides of the equation. Lavoisier, 1788 Chemical Equations

18. not –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. Balancing Equations

19. 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.

20. K + HOH → KOH + H 2 → + We must balance the equation.

21. 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 coefficients are in the lowest possible whole number ratios. (reduced) Steps to Balancing Equations

22. _K + _HOH → _KOH + _H 2

23. 2K + 2HOH → 2KOH + H 2

24. 2K + 2H 2 O → 2KOH + H 2 → + Consider the form of these substances.

25. 2K + 2H 2 O → 2KOH + H 2 → + solid liquid gas

26. 2K (s) + 2H 2 O (l) → 2KOH + H 2(g) → + solid liquid gas What about the KOH?

27. potassium hydroxide (KOH) is a solid at room temperature. However KOH is soluble in water. Substances dissolved in water are said to be aqueous and are indicated as such by an (aq) in the equation.

28. 2K (s) + 2H 2 O (l) → 2KOH + H 2(g) → + solid liquid gas aqueous solution (aq)

29. Solid (cr) or (s) Precipitate ( ↓ ) “Heated” Escaping gas (  ) Catalyst H 2 SO 4 A word may be written above an arrow to indicate something is necessary for the reaction to occur. Other Symbols Used in Equations electricity ∆