chapter 13 notes

# chapter 13 notes - Chapter 13 Chemical Kinetics: Rates and...

This preview shows pages 1–10. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
©2010 Donald L. Siegel, All Rights Reserved Rates of reaction Rates of reaction W Up to now, we’ve only considered whether a reaction not how fast. W The study of the rates of reactions is called kinetics. W We define the reaction rate as the change in concentration of a species per unit time [ ] t A t t t time at A of ion concentrat t time at A of ion concentrat A Rate Δ Δ = = 1 2 1 2 ) (
©2010 Donald L. Siegel, All Rights Reserved Stoichiometry and rates Stoichiometry and rates W Consider the reaction 3A + B 2P W What do we mean by the rate of reaction? W Answer will depend on what we are measuring. A will disappear three times faster than B P will be produced twice as fast as B disappears 1/3(- [A]/ t) = 1/1(- [B]/ t) = ½( P/ t) x x 1 rate reaction of rate ν = ν x is the stoichiometric coeffecient of x

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
©2010 Donald L. Siegel, All Rights Reserved Average and Instantaneous Rates Average and Instantaneous Rates W Rates are usually given as positive numbers For a reactant, Rate = - [A]/ t W Problem with the equation we’ve used is that it’s an average. Rates can change quickly. W Use instantaneous rate The instantaneous rate is the tangent of the [ ] vs. time curve. In calculus terms, d[A]/dt In practical terms, find average over a short time span

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
©2010 Donald L. Siegel, All Rights Reserved Rate Laws Rate Laws W Rates of reactions are not random. W They can be quantified. Any reaction behaves the same way under the same conditions The mathematical description of the kinetic behavior is called a rate law Rate = k[A] a [B] b [C] c a, b, c need not have anything to do with the stoichiometry. W Misinformation in book! Products can appear in the rate law Most often, they don’t.
©2010 Donald L. Siegel, All Rights Reserved More about rate laws More about rate laws W Rate = k[A] a [B] b [C] c Exponents a, b, c, … are the order of the reaction with respect to A, B, C, etc. The order can be anything (integer, fraction). The sum of the exponents a + b + c + … is the overall order of the reaction k is called the rate constant. Don’t confuse it with the rate. W This form of the rate law is called the differential rate law Calculus term. It’s a differential equation There is also an integrated form [] [] [] [] K c b a C B A k dt A d =

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
©2010 Donald L. Siegel, All Rights Reserved Units of k Units of k W The rate of reaction has units of amount/time M/s atm/s mol/s W The units of k can be found from the rate and the total order 1 st order: M/s = k M, k is s -1 2 nd order: k is M -1 s -1
©2010 Donald L. Siegel, All Rights Reserved Determining the rate law Determining the rate law W To avoid the complication of reverse reactions, frequently data is taken early in the reaction. Called method of initial rates

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 11/09/2011 for the course CHEM 162 taught by Professor Siegal during the Spring '08 term at Rutgers.

### Page1 / 51

chapter 13 notes - Chapter 13 Chemical Kinetics: Rates and...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online