C401Ch12LN1

# C401Ch12LN1 - Chapter 12: Chemical Kinetics Part 1 Chemical...

This preview shows pages 1–3. Sign up to view the full content.

Chapter 12: Chemical Kinetics Part 1 Chemical kinetics is the study of how fast chemical reactions occur and how they occur. Four important factors affect rates of reactions: Concentration of reactants. Temperature of reactions. Presence or absence of a catalyst. Surface area of solid or liquid reactants or catalysts. Goal: to understand chemical reactions at the molecular level. Reaction Rates The speed of a reaction is defined as the change that occurs per unit time. It is often determined by measuring the change in concentration of a reactant or product with time. The speed of the chemical reaction is its reaction rate . For a reaction A ± B Here the change in the number of moles of B is defined as: ² (moles of B) = (moles of B at final time) ³ (moles of B at initial time) Illustrate this with an example: Suppose A reacts to form B. Let us begin with 1.00 mol A. • At t = 0 (time zero) there is 1.00 mol A and no B present. • At t = 10 min, there is 0.74 mol A and 0.26 mol B. • At t = 20 min, there is 0.54 mol A and 0.46 mol B. Eventually, there will be no more A left, and only B will be present. We can use this data (and others determined at other times) to find the average rate: For the reaction A ± B there are two ways of measuring rate: The rate of appearance of product B (i.e., change in moles of B per unit time) as in the preceding example. The rate of disappearance of reactant A (i.e., the change in moles of A per unit time). Note the minus sign! This reminds us that rate is being expressed in terms of the disappearance of a reactant. Thus, rates are always positive numbers. in time change B of moles of number in the change rate Average = min mol 026 . 0 0 10 0 0.26 rate Average = ± ± = t ± ± ² = A) of (moles rate Average Average rate = ± (moles B) ± t = (moles of B at t = 10 min) ² (moles of B at t = 0 min) 10 min ² 0 min

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

View Full Document
Rates in Terms of Concentrations In most chemical reactions we will determine the reaction rate by monitoring a change in concentration (of a reactant or product).
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

### Page1 / 5

C401Ch12LN1 - Chapter 12: Chemical Kinetics Part 1 Chemical...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online