Welcome to Teach Me to Science! Today's topic of interest is Rate Laws.
Why you should understand Rate Laws: Rate laws describe the behavior of rates that govern how quickly reactions take place. Our bodies and the world around us rely on chemical reactions. Therefore, understanding how quickly specific reactions occur is very important.
Key Ideas:
- The definition of a Rate Law
- Determining a Rate law
The definition of a Rate Law
A rate law is an expression that defines the rate of a reaction. Recall that the rate of a reaction is only dependent on the reactants. The sample rate law shown below is for the reaction A + B --> products.
A rate law has several key parts. The first is the k value which is the rate constant. The concentration of A and the concentration of B are also included in the rate law because the rate is dependent on how quickly or slowly the reactants are used up.
X and Y in the rate expression describe the reaction orders related to each individual reactant. It is very important to understand that reaction orders can only be determined experimentally and do not correspond with the coefficients in front of the reactants in the balanced equation.
Below is a diagram to help explain what I just wrote in a more visual way.
Determining a Rate law
So what do I mean when I say "reaction orders can only be determined experimentally"? Below is a set of data to help explain.
The data set shows data from three different trials (labeled 1, 2, and 3 on the left-hand side).
Concentrations are shown in molarity (moles/L) and rates are shown in Molarity/second.
Determining the reaction order for each reactant is the first step in writing the rate law. After you've figured out the reaction order (if you forgot how, check out this post). Then you can simply plug in a line of data into the form above and solve for the rate constant.
Summary
-A rate law is an expression that defines the rate of a reaction.
-It is very important to understand that reaction orders can only be determined experimentally and do not correspond with the coefficients in front of the reactants in the balanced equation.
I hope you've found this post on Rate Laws helpful. If you have any questions feel free to comment on this post, email me, or comment on the video I've linked below.
- Saren
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