Post on 21-Jan-2016
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CHEMICAL REACTIONSCHEMICAL REACTIONSThe Process of Chemical Change
– or –“What the heck have I just made?”
CHEMICAL CHANGESCHEMICAL CHANGESIn a chemical change a new
substance is formedSigns of a chemical change
◦Color change◦Change in odor◦Release of a gas◦Precipitate – solid formed suddenly
in a liquid solution
CHEMICAL CHANGESCHEMICAL CHANGESEnergy changes
◦Temperature change◦Flame or explosion◦Luminescence or fluorescence
Chemical equations – a way of describing a reaction
Reactants and products◦reactant 1 + reactant 2 products
CHEMICAL EQUATIONSCHEMICAL EQUATIONSWord equationsacetic acid + sodium bicarbonate
sodium acetate + carbon dioxide
+ waterChemical equationsHC2H3O2 + NaHCO3 NaC2H3O2 + CO2 + H2O
CHEMICAL EQUATIONSCHEMICAL EQUATIONSChange to a chemical equation:Calcium + fluorine gas calcium
fluorideCa + F2 CaF2
Chemical EquationsChemical EquationsSymbols for physical state
(s) = solid(l) = liquid(g) = gas
(aq) = aqueous (dissolved in water)HC2H3O2(aq)+ NaHCO3(s)NaC2H3O2(aq)+ CO2(g)
+H2O(l)
Energy in Chemical Energy in Chemical ReactionsReactionsEnergy in chemical reactions
◦Exothermic reactions – heat is released
◦Reaction vessel feels warmEnergy appears on the right side
of the equation as a productC2H5OH + 3O2 2CO2 + 3H2O + energy
ENERGYENERGYEndothermic reactions
◦Take in energy from the surroundings
◦Reaction container gets cold◦Energy appears on the left side of
the equation as a reactantenergy+Ba(OH)2(s)+2NH4NO3(s)Ba(NO3)2(aq)+2H2O(l)
+2NH3(g)
BALANCING EQUATIONSBALANCING EQUATIONSLaw of conservation of matter
and energy◦Matter and energy cannot be created
or destroyed – only interconverted ◦All the atoms in the reactants show
up in the products
Balancing EquationsBalancing EquationsCoefficients – used to indicate
numbers of molecules or formula units
5NaCl (five formula units of sodium chloride)
2H2O (two molecules of water)
Balancing EquationsBalancing EquationsCounting atoms
5NaCl means five sodium atoms and five
chlorine atoms
2H2Omeans four (2x2) hydrogen atoms and
two oxygen atoms
Balancing EquationsBalancing Equations
3Ca(OH)2
means three calcium atoms, six (3x2) oxygen atoms and six hydrogen atoms Multiply the subscript times the coefficient for every atom in the
parentheses
Balancing EquationsBalancing Equations
4Ba(NO3)2
4 barium atoms, 8 (4x2) nitrogen atoms, and 24 (4x3x2) oxygen atoms
2Na2CO3 . 10H2O
4 (2x2) sodium atoms, 2 carbon atoms, 26 (2x3 + 10x2) oxygen atoms, and
40 (2x10x2) hydrogen atoms
Balancing EquationsBalancing EquationsThere must be the same number of
atoms on each side of the equation
H2 + O2 H2O22H 2O 4H 2O2H 2O 2H 1O
24H 2O 4H 2O
Balancing EquationsBalancing Equations
NaI + BaCl2 NaCl + BaI2(s)21Na 1I 1Ba 2Cl 1Na 1Cl 1Ba 2I1Na 1I 1Ba 2Cl 2Na 2Cl 1Ba 2I2Na 2I 1Ba 2Cl 2Na 2Cl 1Ba 2I
2
•Polyatomic ions can be counted as a group if they appear on both sides
AgNO3 + Na2SO4 Ag2SO4(s)+ NaNO3221Ag 1NO3 2Na 1SO4 2Ag 1SO4 1Na 1NO32Ag 2NO3 2Na 1SO4 2Ag 1SO4 1Na 1NO32Ag 2NO3 2Na 1SO4 2Ag 1SO4 2Na 2NO3
Types of Chemical Types of Chemical ReactionsReactions
Synthesis reaction
A + B CC + O2 CO2
2Na + Cl2 2NaClNa + Cl2 NaCl
Types of Chemical Types of Chemical ReactionsReactions
Decomposition
C A + BH2O H2 + O2
KClO3 KCl + O22KClO3 2KCl + 3O2
(NH4)2Cr2O7N2+4H2O+Cr2O3
22
Types of Chemical Types of Chemical ReactionsReactions
Single displacement
A + BC AC + BMetals displace metals,
nonmetals displace nonmetals
Fe + CuSO4Cu + FeSO4
Cl2+2NaBr(aq)Br2+2NaCl(aq)Cl2+NaBr(aq)Br2+NaCl(aq)
Types of Chemical Types of Chemical ReactionsReactions
Double displacement
AB + CD AD + CBMetals and nonmetals switch partners
NaCl+AgNO3NaNO3+AgCl(s)
2KI + Pb(NO3)2PbI2 + 2KNO3 KI+Pb(NO3)2PbI2(s)+KNO3
Types of Chemical Types of Chemical ReactionsReactions
Combustion Element or compound reacting
with oxygen
2Mg + O2 2MgO
2H2 + O2 2H2O
Combustion ReactionsCombustion ReactionsCarbon containing compounds
give CO2 and water
CH4 + O2 CO2 + H2OCH4 + 2O2CO2+ 2H2O
C2H5OH+O2CO2+H2O C2H5OH+3O22CO2+3H2O
EquilibriumEquilibriumDynamic equilibrium occurs when
the forward and reverse reactions happen at the same rate.
N2 + 3H2 2NH3
At equilibrium, ammonia is being made and decomposed at the same speed.
EquilibriumEquilibrium
At equilibrium, the reaction seems to stop.
In order to achieve equilibrium, reactions must be reversible, or able to occur in both directions.
LeChatelier’s PrincipleLeChatelier’s PrinciplePosition of equilibrium – how
much product and reactant is present at equilibrium
LeChatelier’s principle: If an equilibrium system is stressed, the system will shift to relieve the stress.
LeChatelier’s PrincipleLeChatelier’s PrincipleStresses – adding or removing
reactants, products or energy.
N2+3H22NH3+energy6H2O + CoCl4-2 Co[H2O]6
+2 + 4Cl- + energy
blue pink Add Cl-
Remove Cl-
•Add energy•Remove energy
KineticsKineticsKinetics: reaction rates, or how
fast does a reaction goActivation energy is the energy
required to start a reactionReaction rates are measured in
units of (product)/(unit time)
KineticsKineticsFactors affecting reaction rates
◦Temperature◦Concentration/surface area
Limiting reagent – the reactant that is completely used up in a reaction
◦Catalyst – a substance that speeds a reaction without being used up
KineticsKineticsInhibitor – a substance that slows
a reaction.