chemical reactions – ch 7 notes reactants: zn + i 2 product: zn i 2
TRANSCRIPT
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CHEMICAL REACTIONS CHEMICAL REACTIONS – Ch 7 Notes– Ch 7 Notes
Reactants: Zn + IReactants: Zn + I22 Product: Zn IProduct: Zn I22
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– 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
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Energy is in the bonds!Energy is in the bonds!• ___________ rxns –
bonds _______ and energy is ________
• ___________ rxns – bonds ______ and energy is ________
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– ____________________________ (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
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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.
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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
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– 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
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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?
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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
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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?
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___ Al(s) + ___ Br___ Al(s) + ___ Br22(l) ---> ___ Al(l) ---> ___ Al22BrBr66(s)(s)
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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)
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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
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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?