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Lecture 4

# CHEM102 Lecture Notes - Lecture 4: Rate Equation, Hydrogen Peroxide, Reaction Rate ConstantPremium

2 pages56 viewsWinter 2018

Department
Chemistry
Course Code
CHEM102
Professor
Sai Yiu
Lecture
4

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Chem 102 Lecture 4 Monday, January 15, 2018
Zero order reactions
[A] = - kt + [A]0
Don’t need to memorize it
The trend is usually a linear line that goes down
Half-life
The half-life of a reaction is the time required for a reactant so that half its original
concentration is reacted
t1/2 = [A]0 / 2k
Half-life of zero is dependent on the initial concentration
First order reactions
aA products
ln[A] = -kt + ln[A]0
ln[A] = natural log of concentration of A at time t
ln[A]0 = natural log of initial concentration of A
Another form of first order integrated rate law
[A] = [A]0 e-kt
Half-life for first order reaction is constant
What can we say about the half-life of first-order reactions?
o Half-life of A is always 24 minutes
o For first-order reactions, half-life is independent of initial concentrations
From the half-life of a first-order reaction, the rate constant, k, can be determined
Homework question
Do 1, then substitute that into 2 and 3
Second order reactions
Note: you do not need to memorize formulas, but you need to know which formula is
used for what purpose
1/[A] versus time, t
Reciprocal of the [A], then the reciprocal of the initial concentration
First half-life is short, second one is longer, third one is even longer
Half-life is dependent (inversely proportional) on initial concentration
Summary
First order: k=[A]
Second order: k=[A]2
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