1. 1 CHEMICAL REACTIONS Reactants: Zn + I 2 Product: Zn I 2

2. 2 Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al (s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) The numbers in the front are called Stoichiometric units The letters (s), (g), and (l) are the physical states of compounds.

3. 3 –Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken –Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes. –Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reactionIntroduction

4. 4 The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O 2  CO 2, contains the same information as the English sentence but has quantitative meaning as well.

5. 5 Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 Chemical Equations

6. 6 Solid ___ Liquid (l) Gas ___ Aqueous solution (aq) Catalyst H 2 SO 4 Escaping gas (  ) Change of temperature (  ) Symbols Used in Equations

7. 7 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. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Balancing Equations

8. 8 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.

9. 9 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 AND/OR AND/OR 4 moles of Al + 3 moles of O 2 --- produces  2 moles of Al 2 O 3

10. 10 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

11. 11 Some Suggestions to Help You Some of the Helpful Hints for balancing equations: Take one element at a time, working left to right except for H and O. Save O for next to last, and H 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) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

12. 12 More Rules:  means “yields” and shows direction of action ∆ above arrow shows heat has been added  shows reaction is reversible MINOH: try Metals first, then Ions, then Nonmetals, and Oxygen, then Hydrogen last

13. 13 Rules: 1. LEARN THESE DIATOMIC MOLECULES: O 2 H 2 N 2 F 2 Cl 2 Br 2 I 2 2. The same number of atoms of each element appearing in reactants must appear in the products. 3. The subscripts of a formula cannot be changed to balance the equation. Each compound must retain its stableness via oxidation states. 4. Choose compound with greatest number of atoms first. 5.Balance by placing necessary coefficients in front of entire molecules. NO SUBSCRIPT CHANGES!

14. 14 Rules cont. 6. Be certain each side of equation has same number of atoms of each type. 7. Make sure coefficients are in lowest whole number ratios. 8. (aq.) stands for aqueous which is Latin for water solution: (g) gas (l) liquid (s) solid (c) crystalline solid

15. 15 Balancing chemical equations using the one’s and two’s technique. Example: Balance the equation K + O 2 → K 2 O Solution: Step 1: On the left side of the equation there are 2 oxygen atoms and on the right side of the equation there is one oxygen atoms. Multiply K 2 O by the coefficient of 2 to balance the oxygen atoms. K + O 2 → 2K 2 O Step 2: Balance the K by placing the coefficient of 4 in front of K 4K + O 2 → 2K 2 O Step 3: Check that all the atoms balance and make sure that all coefficients are in the lowest-possible ratio.

16. 16 Balancing chemical equations using the two’s and three’s technique. Example: Balance the equation Fe + O 2 → Fe 2 O 3 Step 1: On the left side of the equation there are 2 oxygen atoms and on the right side of the equation there are 3 oxygen atoms. To balance the oxygen atoms, multiply Fe 2 O 3 by the coefficient of 2 and the O 2 by the coefficient of 3 Fe + 3O 2 → 2Fe 2 O 3 Step 2: Balance the Fe by placing the coefficient of 4 in front of Fe 4Fe + 3O 2 → 2Fe 2 O 3 Step 3: Check that all the atoms balance and make sure that all coefficients are in the lowest-possible ratio.

17. 17 Balancing chemical equations using the even technique. If you have an even number of a certain element on one side of the equation and an odd number of the same element on the other side of the equation, multiply both sides of the equation through by the coefficient of 2. This will give an even number on both sides and make the equation easier to balance. Example: Balance the equation CH 3 OH + O 2 → H 2 O + CO 2 Step 1: Using the CHO technique, we start with carbon, one on each side, so carbon is balanced. There are four H on the left and two on the right, so we place the coefficient of 2 in front of the H 2 O on the right CH 3 OH + O 2 → 2H 2 O + CO 2 Step 2: When we try to balance the oxygen, we find three on the left and four on the right. We multiply both sides of the equation through by two. 2CH 3 OH + 2O 2 → 4H 2 O + 2CO 2 Step 3: The C and H are still balanced, and now there are six O on the left and eight on the right. Change the coefficient in front of the O 2 to 3 to give eight O on the left. 2CH 3 OH + 3O 2 → 4H 2 O + 2CO 2 Step 4: Check that all the atoms balance and make sure that all coefficients are in the lowest- possible ratio.

18. 18 Balancing chemical equations using the CHO technique. If you are balancing equations that have carbon, hydrogen and oxygen atoms then balance the carbon atoms first, the hydrogen atoms second and the oxygen atoms last. Example: Balance the chemical equation C 5 H 12 + O 2 → CO 2 + H 2 O Step 1: Start with C. To balance the C put the coefficient of 5 for CO 2 C 5 H 12 + O 2 → 5CO 2 + H 2 O Step 2: Then, balance the H by placing the coefficient of 6 for H 2 O C 5 H 12 + O 2 → 5CO 2 + 6H 2 O Step 3: Lastly, balance the O by placing the coefficient of 8 for O 2 C 5 H 12 + 8O 2 → 5CO 2 + 6H 2 O Step 4: Check that all the atoms balance and make sure that all coefficients are in the lowest-possible ratio.

19. 19

20. 20 Balancing Equations ___ H 2 (g) + ___ O 2 (g) ---> ___ H 2 O(l) 22 What Happened to the Other Oxygen Atom????? This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H 2 ) combines with one of the oxygen atoms from an oxygen molecule (O 2 ) to form H 2 O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H 2 molecule) to make a second H 2 O molecule.

21. 21 Balancing Equations ___ Al(s) + ___ Br 2 (l) ---> ___ Al 2 Br 6 (s) 23

22. 22 Balancing Equations ____C 3 H 8 (g) + _____ O 2 (g) ----> _____CO 2 (g) + _____ H 2 O(g) ____B 4 H 10 (g) + _____ O 2 (g) ----> ___ B 2 O 3 (g) + _____ H 2 O(g)

23. 23 Balancing Equations Sodium phosphate + iron (III) oxide  sodium oxide + iron (III) phosphate Na 3 PO 4 + Fe 2 O 3 ----> Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O 3 ----> Na 2 O + FePO 4