CHEMICAL REACTIONS CHEMICAL REACTIONS – Ch 7 Notes– Ch 7 Notes

Reactants: Zn + IReactants: Zn + I22 Product: Zn IProduct: Zn I22

– 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?

IntroductionIntroduction

Energy is in the bonds!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 + O2 CO2

Parts of a Reaction Parts of a Reaction EquationEquation

Other symbolsOther symbols• ________________________ - numbers in front - numbers in front

– Show relative amounts of reactants & Show relative amounts of reactants & productsproducts

– Shows the “__________”Shows the “__________”

44 Al Al (s)(s) + + 33 OO2 (g)2 (g) ---> ---> 22 AlAl22OO3 (s)3 (s)

• Letters (s), (g), and (l) are the Letters (s), (g), and (l) are the ___________ states of compounds.___________ states of compounds.

Because of the principle of the Because of the principle of the

______________ ______________

__ _______ _____, ,

an an equation must be equation must be __________________..

It must have the same number It must have the same number of ______ of the of ______ of the same same kind on _____ sides.kind on _____ sides.

Lavoisier, 1788Lavoisier, 1788

Chemical EquationsChemical 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 EquationsBalancing Equations

Subscripts vs. Subscripts vs. CoefficientsCoefficients

Why is it Why is it important NOT important NOT to change the to change the subscripts subscripts when balancing when balancing reactions?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 EquationsSteps to Balancing Equations

Balancing Balancing EquationsEquationsBalancing Balancing EquationsEquations

___ H___ H22(g) + ___ O(g) + ___ O22(g) ---> ___ H(g) ---> ___ H22O(l)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___ Al(s) + ___ Br22(l) ---> ___ Al(l) ---> ___ Al22BrBr66(s)(s)

Balancing Balancing EquationsEquationsBalancing Balancing EquationsEquations

____C____C33HH88(g) + _____ O(g) + _____ O22(g) ---->(g) ---->

_____CO_____CO22(g) + _____ H(g) + _____ H22O(g)O(g)

____B____B44HH1010(g) + _____ O(g) + _____ O22(g) ---->(g) ---->

___ B___ B22OO33(g) + _____ H(g) + _____ H22O(g)O(g)

Balancing EquationsBalancing EquationsBalancing EquationsBalancing EquationsSodium phosphate + iron (III) oxide Sodium phosphate + iron (III) oxide

sodium oxide + iron (III) phosphatesodium oxide + iron (III) phosphate

NaNa33POPO44 + Fe + Fe22OO33 ----> ---->

NaNa22O + FePOO + FePO44

Now Try These:a) P4 + O2 P4O10

b) Li + H2O H2 + LiOHc) Bi(NO3)3 + K2S Bi2S3 + KNO3

d) C2H6 + O2 CO2 + H2O

Mg + O2 MgO 2Mg + O2 2MgO Mg + ½O2 MgO Mg2+ O2 2MgO

4Mg + 2 O2 4MgO

Which Is Balanced?