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
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.
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