Transcript Balancing Chemical Equations G-1(1-4)

Chapter 8
Types of Chemical Reactions
Will the reaction occur?
• If you light a candle, it burns and makes
carbon dioxide and water. Why doesn’t
the reverse reaction occur? Why can’t you
make a candle from carbon dioxide and
water?
Will the reaction occur?
• Driving forces
– Forming a solid (“precipitate)
– Transfer of electrons
– Forming water
– Forming a gas
• Yes, a reaction will occur if one of these
things can happen.
Dissolving ions
• A strong electrolyte completely separates
into ions when it is mixed with water.
– Example: NaCl
NaCl(S)
H2O
Na+(aq) + Cl-(aq)
Complete the equation of silver nitrate dissolving
in water:
AgNO3(s) 
Precipitates
• If you mix NaCl(aq) and AgNO3 (aq) , what
possible products could form?
NaCl(aq) and AgNO3 (aq)  ?
The anions (Cl- and NO3-)change places.
NaCl(aq) and AgNO3 (aq)  NaNO3(aq) + AgCl(s)
• AgCl is a precipitate, so write an “(s)”
• A precipitate is an insoluble solid.
Insoluble = it cannot dissolve in water.
• What is the driving force in this reaction?
Double replacement (continued)
• A double replacement reaction happens when a
precipitate forms.
• Reactants must be aqueous (dissolved in water)
– Example: NaCl dissolved would be shown as NaCl(aq)
• Solubility chart on page 245 will show you when
a precipitate will form.
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Example: KNO3
Soluble or insoluble?
Rule #2: K+ salts are usually soluble.
Answer: Soluble (No precipitate)
Will this double replacement
actually happen??
• Practice: Will this form a reaction?
Li2 SO4(aq )  Ba(ClO3 )2(aq)  ________ (Reacts??)
1.Write the formulas of the possible products (Inside
and outside)
2.Use the solubility chart to determine if any of the
products are INSOLUBLE.
3.If one or both products are insoluble, a chemical
reaction will happen.
• Examples:
– KNO3 and BaCl2
– KOH and Fe(NO3)3
– Na2SO4 and Pb(NO3)
– Annimation:
http://www.mhhe.com/physsci/chemistry/anim
ations/chang_7e_esp/crm3s2_3.swf
Double Replacement
• You should be able to write three types of
chemical equations for double
replacement:
– 1. Molecular equation
– 2. Complete ionic equation
– 3. Net ionic equation
Double Replacement
• The molecular equation shows the
complete formulas of all reactants and
products
NaCl(aq) + AgNO3 (aq)  NaNO3(aq) + AgCl(s)
• The complete ionic equation shows all
strong electrolytes (aq) as ions.
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s)
Double Replacement
• The net ionic equation shows only the
chemicals participating in the reaction.
• Steps:
– Remove the “spectator ions”
– Spectator ions are the same on the reactant
side and the product side (Na+ and NO3-)
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s)
Net ionic equation:
Cl-(aq) + Ag+(aq)  AgCl(s)
8.2
Acid-Base Reactions and
Oxidation-Reduction Reactions
Arrhenius Acids and Bases
• An Arrhenius Acid is a substance that
produces H+ ions when dissolved in water.
• A “strong acid” is an acid that is a strong
electrolyte. It completely separates into H+
and the anion.
HCl  H+ + Cl– Strong acids: HCl, HNO3 and H2SO4
Arrhenius Acids and Bases
• An Arrhenius Base produces OH ions
when dissolved in water.
• A strong base completely separates into
a metal cation and OH• NaOH  Na+ + OH-
Acid-Base Reaction
• Write the molecular equation, complete ionic
equation and net ionic equation for the reaction
of hydrochloric acid and sodium hydroxide.
• Molecular equation
HCl + NaOH  H2O + NaCl
• Complete ionic equation
H+ +Cl- + Na+ + OH-  H2O(l) + Na+ + Cl• Net ionic equation
H+ +OH-  H2O(l)
Acid-Base Reaction
• When an acid and base are mixed, the
products are always water and a salt.
• How do you know a reaction happened?
The solution will be hot.
• An acid-base reaction is the reaction of H+
and OH-
Oxidation Reduction
• In an oxidation-reduction reaction,
electrons move from one chemical to
another.
• Common reactions:
– A metal and a nonmetal react
– Reactions between nonmetals where O2 is a
reactant or product.
Oxidation Reduction
2 electrons
• Ca(s) + Cl2(g)  CaCl2(s)
• Which chemical is losing electrons? How
many electrons?
– Ca loses two electrons
• Which chemical is gaining electrons? How
many electrons?
– Cl gains one electron
Oxidation Reduction
• This happens in two steps:
Ca Ca2+ + 2eCl + e-  Cl• Draw a picture of this reaction:
Mg(s) + CuCl2(s)  Cu(s) + MgCl2(s)
Which chemical loses electrons? How
many?
Which chemical gains electrons? How
many?
8.3
Types of reactions & “How do we
know IF it will happen?”
Classifying reactions
• Looking at a chemical equation, be able to
classify it…
• Based on driving force:
– 1. Precipitation reactions
– 2. Oxidation-reduction reactions
– 3. Acid-base reactions
• Types of oxidation-reduction reactions:
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1. Combustion reactions
2. Synthesis reactions
3. Decomposition reactions
4. Single Replacement
Double Replacement
AX+BY → AY +BX
• Each anion changes places with the cation.
• Example: sodium sulfate + copper (II) chloride
Single Replacement:
A+BX → AX +B
• A = a metal or group 7 element.
• B = metal, group 7 element or hydrogen
• X = anion
• A replaces B in the BX compound.
• Example:
Zn(s) +2HCl(aq)  H2(g) + ZnCl2(aq)
Synthesis Reactions
• Synthesis– 2 or more substances combine to
form one, bigger molecule.
• General formula…
A  B  AB
• Example: Combustion of Ca
• Ca + O2  CaO
Decomposition Reactions
• Decomposition– one substance splits to form
several smaller molecules/atoms.
• General formula…
AB  A  B
• Example: Breaking water molecules.
• What equation will it have? (it’s a reaction that
results in Hydrogen gas, H2, and Oxygen,O2)
• Usually requires energy input (heat, electricity,
etc), because we are breaking bonds.
Combustion Reactions
Combustion Reactions
• Combustion – a substance combines with
oxygen. When they react they release energy,
water vapor and carbon dioxide.
• Will need to balance these
• Ex: C2H5OH + O2  CO2 + H2O
Classifying reactions
• Practice: Classify this reaction in as many
ways as possible
• 2Ca + O2  2CaO
• This is classified as a synthesis and
combustion. It is also an oxidationreduction reaction.