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

2 pages56 viewsWinter 2018

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**preview**shows half of the first page. to view the full**2 pages of the document.**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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