drill: calculate the osmotic pressure of 5.0 g naoh in 7500 ml soln at 27 o c
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Drill: Calculate the osmotic
pressure of 5.0 g NaOH in 7500
mL soln at 27oC.
Drill: Calculate the heat change when 25.0 g of H2O goes from 66.3oC
to 26.3oC.Cwater = 4.18 J/gK
Chemical Kinetics or
Reaction Rates
Reaction Rate•The speed at which reactants become products in a chemical reaction
•M/s = mole/Ls
Kinetic Theory• All matter is made up of
tiny particles
• The particles are in constant motion
• All collisions are elastic ?
Elastic Collisions•Collisions in which there is no energy change
Particles Reacting•For particles to react, they must collide
•Reaction rate is dependent on collision rate
Particles Reacting• When a reaction takes place,
an energy change occurs
• Collisions (in which reactions occur) are not elastic
Reaction Rate•Rate = - d[Reactant]/dt
•Rate = +d[Product]/dt
•M/s
Factors Affecting Rxn Rate
• Concentration, Temperature, Agitation, Process, Orientation, Catalyst, SA of Solid, Pressure of Gas, Reaction Mechanism
Drill:List & describe at least 5 factors that will affect reaction
rates
Rate Expression•An equation showing how rate depends on the number of reactants in a rate determining reaction
Rate Expression
•Rxn: aA(aq) + bB(aq)
P•Expr: Rate = k[A]a[B]b
•[A] = molarity of A
Rate Expression
•Rxn: aA(g) + bB(g)
Product
•Exp: Rate = kPAaPB
b
Write Rate Expressions for:
H2(g) + N2(g) NH3(g)
HCl(aq) + Ba(OH)2(aq)
BaCl2(aq) + H2O (l)
Write Rate Expressions for:
H2(g) + N2(g) NH3(g)
Rate = k(PH2)3(PN2)
Write Rate Expressions for:
2HCl(aq) + 1Ba(OH)2(aq)
1BaCl2(aq) + 2H2O (l)
Rate =
k[HCl]2[Ba(OH)2]
Write Rate Expressions for:
1 Cl2(g) + 1 HOOH (aq)
2 HOCl(aq)
Write Rate Expressions for:
1 Cl2(g) + 1 HOOH (aq)
2 HOCl(aq)
Rate = k(PCl2) or
Rate = k[HOOH]
Write the Rate Law for:
2A(aq) + B(aq) + 3C(s)
Products
Write the Rate Law for:
2A(aq)+ B(aq)+ 3C(s) P
Rate = k[A]2[B]
Reaction Order•The total number of reactants (coefficients)
•Equals total exponents in rate expression
Drill: Write the rate expression & determine
rxn order for:
SO2(g) + O2 (g)
SO3(g)
Drill: Write the rate expression & determine rxn order for:
2 SO2(g) + 1 O2 (g)
2 SO3(g)
Rate = k(PSO2)2(PO2)
Determining Rxn Order
• Find rate expression ratios
• (Ratio of concentrations)x = rate ratio
• x = exponent
Write the rate expression for:
aA + bB
Products
All aqueous
The next slide includes data from an experiment where various concentrations of A & B were added together, and the rates of product
formation was measured.
Experimental ResultsExp [A] [B] Rate
1 1.0 1.0 2
2 2.0 1.0 4
3 1.0 2.0 8
Experimental ResultsExp [A] [B] Rate
1 1.0 1.0 2
2 2.0 1.0 4
3 1.0 2.0 8
Write the rate expression for:
aA + bB + cC
Products
All aqueous
Experimental ResultsExp # [A] [B] [C] Rate
1 0.1 0.1 0.1 3
2 0.3 0.1 0.1 81
3 0.1 0.3 0.1 27
4 0.1 0.1 0.3 3
Experimental ResultsExp # [A] [B] [C] Rate
1 0.1 0.1 0.1 3
2 0.3 0.1 0.1 81
3 0.1 0.3 0.1 27
4 0.1 0.1 0.3 3
Solve All: Exp Data:Exp # [R] [S] [T] Rate
1) 0.25 0.20 0.10 2
2) 0.25 0.60 0.10 18
3) 0.50 0.20 0.10 4
4) 0.25 0.20 0.40 32
Solve All: Exp Data:Exp # [R] [S] [T] Rate
1) 0.25 0.20 0.10 2
2) 0.25 0.60 0.10 18
3) 0.50 0.20 0.10 4
4) 0.25 0.20 0.40 32
Drill: Solve AllExp Data:
Exp # [R] [S] Rate
1) 0.25 0.20 2
2) 0.25 0.60 18
3) 0.50 0.20 4
Solve All: Exp Data:
Exp # [R] [S] Rate
1) 0.25 0.20 2
2) 0.25 0.60 18
3) 0.50 0.20 4
Solving exponents with a calculator.
Ax = B
Ax = B
Log Ax = log B
xLog A = log B
Thus:
x =Log BLog A
Clausius-Claperon Eq
Ea= R ln(T2)(T1) k2
(T2 – T1) k1
Calculate the activation energy of a reaction
whose rate constant is 2.0 x 103 at 27oC and is
2.0 x 106 at 77oC:
Drill:List & describe at least 5 factors that will affect reaction
rates
Half-Life•The time required for one half of the reactants to change into products
in a reaction
Useful RelationshipsRxn Order Rate Exp
0 Rate = k
1 Rate = k[A]
2 Rate = k[A]2
1st Order Age Dating Formula t = ln(Ai/Af)t1/2
0.693
Reaction Mechanism
•The sequence of steps that make up
the reaction process
Reaction Mechanism
Step 1 A B fast
Step 2 B C slow
Step 3 C D fast
Total A D
Reaction Mechanism•The rate determining
step in a reaction mechanism is the
slowest step
Reaction Mechanism
•To solve the rate expression, you
must use the slowest step
Solve Rate Expression
A + B C + D fast
2C + A G fast
2D + B K fast
2G + 2K Prod. slow
Solve Rate Expression
X + Y M + N fast
M + N 2G slow
2N + G K fast
2G + 2K Prod. fast
Solve All: Exp DataExp # T [A] [B] Rate
1) 27oC 0.10 0.10 2
2) 27oC 0.30 0.10 18
3) 27oC 0.10 0.20 4
4) 77oC 0.10 0.10 20
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140 160
Time (s)
Tem
per
atu
re (
C)
Solving Rxn ExponentRate2 k [IO3
-]x[S2O5-2]y
Rate2 k [IO3-]x[S2O5
-2]y
M/31 s k(0.10M)x(0.10M)y
M/66 s k(0.10M)x(0.05M)y
=
=
Plot of Absorbance vs Wavelength
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
400 450 500 550 600 650 700
Wavelength (nm)
Ab
sorb
ance
[Z]Abs 640
0.1 0.66
0.075 0.495
0.05 0.33
0.025 0.165
0.01 0.066
Plot of Abs vs Concentration
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.02 0.04 0.06 0.08 0.1 0.12
Concentration (M)
Ab
sorb
ance
Drill: Solve Rate Expr:
X + Y M + N fast
3M + N 2G fast
2N K fast
2G + K Prod. slow
Rate Law & Net RxnA + B C + D fast
4C + A 2G fast
4D + B 2K fast
G + K Q + W slow
Q + 2 W Prod. fast
Review
Drill: Determine AllExp # T [A] [B] Rate
1) 27oC 0.10 0.10 2
2) 27oC 0.30 0.10 54
3) 27oC 0.10 0.20 8
4) 77oC 0.10 0.10 200
Solve Rate ExpressionA + B C + D fast
4 C + A 2G fast
2 K 4D + B fast
G + K Q + W fast
2Q + 2W Prod. slow
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