Download - CHEMICAL REACTIONS Reactants: Zn + I 2 Product: Zn I 2 Chem I: Chapter 6 Chem IH: Chapter 11
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CHEMICAL REACTIONSCHEMICAL REACTIONS
Reactants: Zn + IReactants: Zn + I22 Product: Zn IProduct: Zn I22
Chem I: Chapter 6Chem IH: Chapter 11
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Chemical Reactions…
•occur when bonds between valence electrons of atoms are formed or broken
• involve changes in matter, the making of new materials with new properties & energy changes
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Signs of Chemical Reactions(These signs usually indicate a chemical rxn has occurred.)
1. Color change (ex: KMnO4)2. Formation of precipitate 3. Odor change (ex: spoiled milk)4. Gas release (baking soda & vinegar)5. Energy change- (vermiculite)
–heat absorbed –heat or light released
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Using EquationsUsing EquationsEquations represent chemical
rxns. They show what is happening.
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Rules All Equations Follow• Show reactants (“before”) on the left,
products (“after”) on the right
• Use an arrow() to separate reactants from products
• Use + signs between reactants
• Use + signs between productsEx:aluminumaluminum+ + oxygenoxygenaluminum aluminum
oxideoxide
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2 Ways to Write an Equation
1. Word Equations-
• use names of compounds & elements.
Ex: Ex: aluminumaluminum++oxygenoxygenaluminum oxidealuminum oxide
• don’t tell you how much reactant or product is involved.
• Write this equation first
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2. 2. Chemical EquationsChemical Equations• Show the relative amounts of Show the relative amounts of
reactantsreactants and and productsproducts in a reaction in a reaction• Symbols represent elements
Ex: Al• Formulas represent compounds
Ex: OO22 & AlAl22OO33
• Coefficients are the numbers in front of the symbols or formulas. They show how many units (atoms, molecules, etc.)
44 AlAl (s)(s) + + 33 OO22 (g) (g) ---> ---> 22 AlAl22OO33 (s) (s)
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Additional Rules Chemical Equations
Follow• Physical state Physical state of chemicals is shown after of chemicals is shown after the formula or symbolthe formula or symbol
(s) = solid(s) = solid (l) = liquid(l) = liquid(g) = gas(g) = gas (aq) = in aqueous solution(aq) = in aqueous solution
• EnergyEnergy is shown when it is an important is shown when it is an important part of a rxn.part of a rxn.
• With the With the reactantsreactants in endothermic rxns in endothermic rxns• With the With the products products in exothermic rxnsin exothermic rxns
• BalanceBalance-equations must be balanced-equations must be balanced
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• Charcoal, which is basically carbon, reacts with oxygen to yield carbon dioxide.
• Word eq’n: carbon + oxygen carbon dioxide+ energy
• Chemical equation: C(s) + O2(g) CO2(g) + energy
has a quantitative meaning as well.
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Balancing Chemical Balancing Chemical EquationsEquations
Because of the principle of Because of the principle of the the conservation of conservation of
mattermatter, an , an equation equation
must be balancedmust be balanced..
Def: It must have the Def: It must have the
same number of atoms of the same number of atoms of the same kind on both sides.same kind on both sides.
Lavoisier, 1788Lavoisier, 1788
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Balancing Chemical Balancing Chemical Equations, Equations, cont.cont.
Balancing Chemical Balancing Chemical Equations, Equations, cont.cont.
44 Al(s)Al(s) + + 33OO22(g)--->(g)--->22 AlAl22OO33(s)(s)
This equation meansThis equation means4 4 AlAl atoms +atoms + 33 OO22 molecules molecules
---produces--->---produces--->
2 2 units of units of AlAl22OO33
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Balancing Equations, Balancing Equations, cont.cont.• When balancing a chemical
equation you may ONLY add coefficients in front of the compounds & elements to balance the reaction.
• You may notnot change subscripts b/c this changes the compound.
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Subscripts vs. Subscripts vs. CoefficientsCoefficients• SubscriptsSubscripts tell tell
you how many you how many atoms of an atoms of an element are in a element are in a compound.compound. Ex: Ex: the “2” in Othe “2” in O22..
• CoefficientsCoefficients tell tell you the quan-you the quan-tity, or number, tity, or number, of units of a of units of a chemical. chemical. Ex: Ex: the “3” in front the “3” in front of COof CO22.←.←
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4 Steps to Balancing 4 Steps to Balancing EquationsEquations
Step #1: Write the correct symbols & formulas for the reactants and the products.
• (DO NOT TRY TO BALANCE IT YET! Just write the correct formulas first.
• And most importantly, once you write them correctly, DO NOT CHANGE THE FORMULAS!)
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HINT: WHEN COMPLETING STEP #1
When writing formulas, remember
•The 7 diatomic elements –H2, N2, O2, F2, Cl2, Br2, I2
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4 Steps to Balancing 4 Steps to Balancing EquationsEquations
Step #2. Count the number of atoms for each element on the left side.
Count the number of the atoms of each element on the right side.
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4 Steps to Balancing 4 Steps to Balancing EquationsEquations
Step #3: Determine where to place coefficients in front of symbols & formulas so that the left side has the same number of atoms as the right side for EACH element.
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Steps to Balancing EquationsSteps to Balancing Equations
Step # 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)
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Some Suggestions to Help Some Suggestions to Help YouYouHelpful Hints for balancing equations:
• Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last.
• For polyatomic ions that appear on both sides of the equation count ions, not atoms.
• Water may be considered ionic, made up of H+ and OH-, if helpful.
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Practice Problem
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Balancing Balancing EquationsEquationsBalancing Balancing EquationsEquations
__ H__ H22(g) + ___ O(g) + ___ O22(g) ---> __ H(g) ---> __ H22O(l)O(l)2
What Happened to the Other Oxygen Atom?????
This equation is not balanced!
LEFT SIDE RIGHT SIDEH=2 H=2O=2 O=1
2
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ANSWER TO PRIOR SLIDE
• Re-Count the atoms
__22_H_H22(g) + ___O(g) + ___O22(g) --->_(g) --->_22_H_H22O(l)O(l)
• LEFT SIDE RIGHT SIDE
• H=4 H=4• O=2 O=2
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Balancing Balancing Equations EquationsBalancing Balancing Equations Equations
___ Al(s) + ___ Br___ Al(s) + ___ Br22(l) ---> ___ Al(l) ---> ___ Al22BrBr66(s)(s)2 3
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Practice Practice Balancing Balancing EquationsEquations
Practice Practice Balancing 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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5 Types of Reactions1. Combination(Synthesis)-2 or
more reactants combine to form 1 product. Ex: 2H2 + O2 2H2O
2. Decomposition- 1 reactant breaks down into 2 or more products.
Ex: 2H2O 2H2 + O2
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5 Types of Reactions, cont.
3. Single Replacement- 1 element replaces another in a compound
Ex: 2K + H2O 2KOH + H2
(K replaced H in water)
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5 Types of Reactions, cont.4. Double Replacement-
exchange of cations be-tween 2 ionic compounds
Ex: 2NaCN +H2SO42HCN + Na2SO4
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5 Types of Reactions, cont.5. Combustiontion-the-the rapid combination
of a substance w/oxygen to form heat & light.
• Reactants are made of C,H, and sometimes O.
• Products are CO2, H2O, (and energy).
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5 Types of Reactions, cont.
5. Combustiontion• Ex 1: CH4 + 2O2 CO2 + 2H2O
+ energy• Ex 2: Mg + O2 2MgO +energy(note: Ex2 is also a synthesis rxn)
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Practice Problems: What type of reaction?
1. Na1. Na33POPO44 + Fe + Fe22OO33 NaNa22O +FePOO +FePO44
2. C2. C33HH88(g)+O(g)+O22(g)(g)COCO22(g) + H(g) + H22O(g)O(g)
3. 2Al(s) + 3Br3. 2Al(s) + 3Br22(l) ---> Al(l) ---> Al22BrBr66(s)(s)
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Answers to Practice Problems:
What type of reaction?1.1. NaNa33POPO44 + Fe + Fe22OO33 NaNa22O +FePOO +FePO44
Double replacementDouble replacement
2. C2. C33HH88(g)+O(g)+O22(g)(g)COCO22(g) + H(g) + H22O(g)O(g)
combustioncombustion
3. 2Al(s) + 3Br3. 2Al(s) + 3Br22(l) ---> Al(l) ---> Al22BrBr66(s)(s)
synthesissynthesis
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Activity Series (Single Replacement)
• Not all combinations of chemicals will produce a reaction.
• An ion that is more reactive will replace a less reactive ion in a compound.
• Copy the Activity Series of Metals Table onto your P. Table. (also on p333 of text)
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Activity Series of Metals
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Activity Series of Halogens
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Practice Problems• Complete Q#1- from p
____ of text.• Q& A please!