Unit 3 (chapter 6) Flashcards
Chemical kinetics
Study of chemical rates of reaction
Rate of reaction
How quickly (or slowly) reactants disappear and products or form
Rate of reaction
Change in conc. (reactants or products)/ change in time
Measuring rates of reaction
- Use conductivity (ions produced)
- Use volume/ pressure (gas produced)
- Use spectrophotometer (color change)
Factors effecting reaction rates
chemical nature of reactants, ability for reactants to come in contact, concentration of reactants, temperature of reaction system, pressure of a catalyst
Chemical nature of reactants
Chemical reactivity depends on the tendency towards bond formation (ex. sodium reacts quickly with O2, fe does not)
The ability for reactants to come into contact
Individual molecules must interact, rxns are usually done in the liquid of gas phases
A heterogeneous rxn occurs when reactants are in two or more phases
The rate of rxn is controlled by the area at the interface and the size of the particles
The concentration of reactants
Increasing conc. speeds up reaction
The temperature of the reaction system
Most occur faster at higher temperatures
The presence of a catalyst
catalysts are substances that increase the rate of reaction without being consumed in the reaction
Collision theory
A chemical system consists of particles that are in constant random motion at various speeds. The average kinetic energy of the particles is proportional to the temperature of the sample
A chemical reaction must be an effective collision between particles- it mist have sufficient energy and correct orientation so that bonds can be broken and new bonds can be formed
The rate of reaction depends on the frequency of the collisions and the fraction of those collisions that are effective
Activated complex
Contains partially broken and partially formed bonds ie. transition state
Activation energy
The minimum energy with which particles must collide to produce and effective collision
Reaction mechanisms
It is highly unlikely for 3 or more molecules to collide simultaneously. Rxns involving many molecules are more likely to occur in a series of steps. Each step is called an elementary process and collectively the sequence of steps is the reaction mechanism
Rate intermediates
stable compounds that appear during a rxn sequence but disappear in the formation of a product
