AP Chem Chapter 5: Kinetics

Rate of chemical reaction equals

change in concentration/time (basically average velocity)

Measured in M/s (moles per second)

Each species is divided by its respective coefficient

If given the reaction rate of one compound in a chemical equation, you can…

Use the mole ratios of the other compounds to find the reaction rates. Remember if it is a Reactant, there is a NEGATIVE, and if it is a product, it is positive

Factors that affect Reaction Rate

* Reactant Concentration (M)
* Surface Area
* Temperature
* Use of catalysts/enzymes

If given the reaction rate of different concentrations of A and B, you can determine the Rate Law with…

The formula R = k•\[A\]^x•\[B\]^y

Where R is reaction rate

k is the rate constant

x is the order of A

y is the order of B

The OVERALL order of the equation is x+y

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To find x and y, think about what power of a number that A and B have to be multiplied by will get the result (when the opposite A or B is *held constant*)

To find the rate constant, plug in A, B and R to solve.

Finding the Units of the rate constant

Units changed based on the rate law / order of A and B (molarity and reaction rate)

Rate of a 0 order is M/s, 1 is 1/s, 2 is 1/M•s

Manipulate the rate law formula by plugging in an M for A and B with the respective orders as well as an M/s for the reaction rate and solve using algebra

How to find the rate order given a Rate-Concentration Graph

If the line is…

Horizontal/flat = 0

Linear = 1

Exponential = 2

Steeper Exponential = 3

The Integrated Rate Law for 1st order is…

ln\[A\]t = -k•t + ln\[A\]0

Also can be written as ln\[At/A0\] = -k•t using log properties

Linear/straight line (with a slope of -k and a y-intercept of ln\[A\]0)

Takes the form of y=mx+b when graphed

**Always has a negative slope**

In relation to molarity, pressure has a ____ relationship

DIRECT

Using PV = nRT, you can see that P= nRT/V

Since n/V is molarity, P also equals MRT. Thus, M is directly proportional to P.

When using rate law, gases use pressure rather than concentration because it’s easier to measure

If given the time and pressure of a gas, you can find its order by…

Treating time as the x and adding a third column, which will be the natural log of P. This will be the y axis and the relationship between x and y when graphed will tell you the order.

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To find the rate constant, find the slope of the line.

Half life of a first-order reaction.

Rewriting the integrated gas law as \[A\]t = \[A0\]•e^-kt, we can graph the equation like exponential decay.

Manipulating the formula and taking the natural log of 1/2, you get half life = .693/k

Integrated Rate Law for Second Order

You know that the reaction is second order if it forms a linear relationship when time is graphed against 1/M. Slope is really 2k since it is second order.

**Always has a positive slope**

Integrated Rate Law for Zero Order

Zero order if straight line when time is graphed against \[A\]0

A zero order reaction means that increasing concentration has NO effect on reaction rate.

**Always has a negative slope**

If the coefficient in front of A is not one…

the slope becomes x•k, where x is the coefficient of A

In terms of reaction order, radioactive decay is…

A FIRST order reaction