CHEMICAL REACTIONS – Ch 7 Notes Reactants: Zn + I 2 Product: Zn I 2

–Chemical reactions occur when _______ between atoms are _______ or ________ –Chemical reactions involve ________ in matter, the making of _____ materials with ______ properties, and _______ changes. –Chemical reactions are written in symbolic form. –How can you tell a chemical reaction is happening?Introduction

Energy is in the bonds! ___________ rxns – bonds _______ and energy is ________ ___________ rxns – bonds ______ and energy is ________

–______________ –______________ (molecules on left of arrow) –______________ –______________ (molecules on right of arrow). –“ + ” sign separates molecules on same side – “  ” is read as “____________” – Ex: carbon plus oxygen react to yield carbon dioxide C + O 2  CO 2 Parts of a Reaction Equation

Other symbols ____________ - numbers in front____________ - numbers in front –Show relative amounts of reactants & products –Shows the “__________” 4 Al (s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s) Letters (s), (g), and (l) are the ___________ states of compounds.Letters (s), (g), and (l) are the ___________ states of compounds.

Because of the principle of the ______________ __ _____, an equation must be _________. It must have the same number of ______ of the same kind on _____ sides. Lavoisier, 1788 Chemical Equations

___ –When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may ___ 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

Subscripts vs. Coefficients Why is it important NOT to change the subscripts when balancing reactions?

1. DO NOT CHANGE THE _________________! 2. Always start on the ___________. 3. Compare the number of _____ for each element on either side of the reaction 4. Add or change ________________ to balance. 5. Every time you make a change, go back to the _______________. 6. If polyatomic ions are present on both sides, treat them as one unit. 7. Check your answer. Steps to Balancing Equations

Balancing Equations ___ H 2 (g) + ___ O 2 (g) ---> ___ H 2 O(l) What Happened to the Other Oxygen Atom????? This equation is not balanced! What coefficients need to be added to balance this equation?

___ Al(s) + ___ Br 2 (l) ---> ___ Al 2 Br 6 (s)

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)

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

Now Try These: a)P 4 + O 2  P 4 O 10 b)Li + H 2 O  H 2 + LiOH c)Bi(NO 3 ) 3 + K 2 S  Bi 2 S 3 + KNO 3 d)C 2 H 6 + O 2  CO 2 + H 2 O Mg + O 2  MgO 2Mg + O 2  2MgO Mg + ½O 2  MgO Mg 2 + O 2  2MgO 4Mg + 2O 2  4MgO Which Is Balanced?