Home > Chemistry, Uncategorized > Bonus Lecture: Principles of Chemical Science – Lecture 31 Notes

Bonus Lecture: Principles of Chemical Science – Lecture 31 Notes

Overview

This is a nice, brief lecture on chemical kinetics. Today’s lecture is only 40 minutes long.

Details

A reaction may be favorable but may take an extremely long time.  Whether or not a reaction is favorable is a thermodynamic question.

C6H12O6 + 6O2 = 6CO2 + 6H2O + 36ATP

G = H – TS

S is positive so disorder is increasing, the reaction is exothermic so H is negative, making G overall negative.

Inertness refers to lability or non-lability, the ability to decompose.  The G term will dictate whether the compound is non-labile, labile, or at equilibrium.

Reaction rate is affected by temperature, concentration, catalysis, material nature, and mechanism.

Rate = – d[reactants]/dt = +d[products]/dt

2HI = H2 + I2

Rate = -d[HI]/2dt =+d[H2]/dt = +d[I2]/dt

Those were rate expression.  A rate law is the relationship between rates and concentrations.  These are related by a proportionality constant, k.  This is experimentally determined.

Rate = k [A]^n[B]^m

The rate law is an experimental result.  You cannot just look at the stoichemetry unless the reaction is relatively simple.

aA + bB = cC + dD

k = [A]^a/dt = [B]^b/dt = -[C]^c/dt = -[D]^d/st

M = 1 is first order

k [A] = rate

M = 2 is second order

k[A]^2 = rate

M = -1

k/[A] = rate

M = 1/2

k [A]^.5 = rate

M = 0

k = rate

Basically, you look at various concentrations then see what that does to the reaction rate.

Rate laws are not the same as reaction rates.

The overall rate law is the sum of the exponents.  For the generalized reaction:

ath order in A, bth order in B, and a+b overall.

The units for the rate constant vary.  You’ll have to perform to dimensional analysis to discover it.

Data is often imperfect.  Concentrations may not change very much over brief intervals of time.  Integrated rate laws can be used.

Reaction Order Differential Rate Law Integrated Rate Law Characteristic Kinetic Plot Slope of Kinetic Plot Units of Rate Constant
Zero
d [A] d t = k
[A]  =  [A]0k t [A] vs t k mole L-1 sec-1
First
d [A] d t = k [A]
[A]  =  [A]0 ek t ln [A] vs t k sec-1
Second
d [A] d t = k [A]2
[A] = [A]0 1 + k t [A]0
1/[A] vs t k L mole-1 sec-1

Half life is the time taht it takes for the original material to decay to half of the oringinal value.  Half life does not depend upon concentration.

Review

PV = nRT

K = products/reactants

aA + bB = cC + dD

IGL: random motion, point source, elastic collisions, high temperature, low pressure

Tissues: epithelial, nervous, muscular, connective

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