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

2 Chemical Equations 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) Numbers in the front : coefficients- coefficients- amount of molecules or ions amount of molecules or ions The letters (s), (g), and (l) are the physical states of compounds.

3 Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken Chemical reactions involve chemical change making new materials with new properties + energy changes. Symbols represent elements Formulas describe compounds Chemical equations describe a chemical reactionIntroduction

4 The charcoal used in a grill is basically carbon (C). The carbon reacts with oxygen to yield carbon dioxide. C + O 2  CO 2 This reaction is a concise sentence that also is quantitative.

5 During a chemical change mass is conserved, or remains the same. All the atoms are still present, but in a different arrangement. Lavoisier, 1788 Conservation of Matter

6 Once the formulas are written correctly…….do NOT change the subscripts!!!! *changing the subscript changes the compound* NaCl is not Na 2 Cl 2 H 2 O is not H 2 O 2 Coefficients are added in front of the formula indicates the amount that is present--- this satisfies the Law of Conservation of Matter Balancing Equations

7 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.

8 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 2 molecules of Al 2 O 3 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

9 1.Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! 2.Do an Atom Inventory 3.Use coefficients in front of formulas to balance the reaction 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

10 Some Suggestions to Help You Take ONE element at a time work from left to right leave H and O until the end If everything balances except O with a whole # ….2x the coefficients Polyatomic ions that are on both sides of the equation should be kept together in the atom inventory If H 2 O is on one side of the equation and OH -1 is on the other, write H 2 O as HOH

11

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

13 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)

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