Chemical Kinetics Chemical Reaction Rates (13.2) The Effect of Concentration on Reaction Rate (13.3) Book Pages - (598-607)

The Rate of a Chemical Reaction Rate of a Chemical Reaction - A measure of the speed at which a reaction occurs. The rate of a chemical reaction is measured in Mols per Second (M/s) and can be displayed as:

Reaction Rate is always the same for a given equation This means that you can find the reaction rate for an equation using any of the reactants or products. Equation for a reactant: Equation for a product:

Example: In the first 10 seconds, the concentration of dropped from 1.0M to 0.868M. Calculate the average rate of reaction. Calculate

Example:

Example

Problem: In the first 25 seconds of the reaction, the concentration of [HBr] dropped from 0.600M to 0.512M. Calculate the average rate of reaction during this interval. 0.00176 M/s = Rate

Interpreting a Graph Reactant Concentration will always decrease. Product Concentration will always increase.

The instantaneous reaction rate is the reaction rate at any one point in time. Defined as Defined as

Measuring Reaction Rate Through Experimentation Spectroscopy - a way of measuring reaction rates using light. Spectroscopy works by firing light into a colored gas and measuring the amount of light absorption after a given time period. Polarimetry - You can measure reaction rate by measuring the degree at which a solution polarizes light during a time period. Another way of measuring the rate of reaction is by measuring the change in pressure caused by the reaction.

The Rate Law The rate of a reaction often depends of the concentration of one or more reactants. Rate Law k = rate constant n = reaction order Reaction order determines the effect the concentration of the reactant will have on the overall rate of reaction

Reaction Order n = 0 n = 1 n = 2 Reaction is in zero order The concentration of a reactant in a zero order reaction does not affect the rate of reaction. n = 1 Reaction is in first order The concentration of the reactant is directly proportional to the rate of reaction. n = 2 Reaction is in second order Reaction rate is directly proportional to the square of the reactant concentration.

Zero Order Reactant concentration decreases linearly Reaction rate stays constant as concentration increases Occurs when the amount available for reaction is unaffected by the change in quantity of reactant Sublimation

First Order Rate of reaction is directly proportional to concentration of the reactant As the amount of reactant decreases, the reaction slows down Reaction rate speeds up with a higher reactant concentration in a linear relationship

Second Order Rate of reaction is directly proportional to the square of the reactant concentration Rate of reaction is much more dependent on the concentration of the reactant

How the heck to I determine a Reaction Order You gotta do some experimentation. Reaction Order can only be determined through experimentation. The most popular technique for finding the reaction order is called the Method of Initial Rates.

Method of Initial Rates The initial rate is found by running the reaction multiple times with different initial concentrations. This determines the overall effect of concentration on the rate of reaction. Concentration [A] is directly proportional to the initial reaction rate, making this a first order reaction.

Solving for k Super easy -

Zero Order Units (k) = First Order Second Order

Reaction Order of Multiple Reactants It’s basically the same thing, but now there is the overall order of the reaction. Overall order is the sum of all of the exponents in the rate law equation. This can only be found through experimentation as well.

What the heck is on the AP Reaction Rates Rate Laws (know how to write the equation) Interpreting Graphs Basically everything else in these slides