Chapter 10 Rate of reaction Flashcards
What is meant by rate of reactionx2
how fast a reactant is used up
or how fast a product is formed
Equation for rate of reaction
rate= change in concentration÷ time
unit for ‘theoretical’ rate of reaction
moldm^-1s^-1
Factors affecting RoR
Temp
Concentration (or pressure with liquids)
Presence of a catalyst
Surface area of solids
Collision theory?
For a reaction to occur , particles must come together and collide with the correct orientation and an energy greater than the activation energy of the reaction
Explain affect of higher concentration/increased pressure
More particles in a given volume so more FREQUENT collisions so faster RoR
What is the criteria for the properties we can measure to find RoR 2
Changes during the reaction
Proportional to conc
When monitoring RoR by has collection when should the stop clock be started
when bung is replaced
Two methods of monitoring RoR when a gas is produced
Gas collection
Mass loss
why is cotton wool used in the monitoring by mass loss experiment and why will it have no negative affect on the experiment
Stop spray of solution caused by fizzing escaping, permeable enough to let gas escape
Catalyst?
substance that increases rate of chemical reaction without undergoing any permanent change itself
Characteristics of catalysts 4
Not used up in the chemical reaction
May react with the reactant to form an intermediate
May provide a surface of which the reaction takes place
At the end of a reaction it is always regenerated
How do catalysts increase RoR
Provides an alternative reaction pathway with a lower activation energy
Symbol for activation energy with the presence of a catalyst
E sub c
Homogeneous catalyst?
Has same physical state as the REACTANTS
Example of when homogeneous catalyst is used
Ozone depletion
Heterogeneous catalyst
Catalyst has a different physical state from the reactants
Adsorption
Formation of weak bonds with the catalyst surface during use of a heterogeneous catalysts
Steps in the use of a heterogeneous catalyst
Adsorption
Bonds within reactant molecules break
New bonds form to produce product molecules
Desorption
Desorption
Product molecules leave the surface of a heterogeneous catalyst
Economic and environmental importance of catalysts 4
Catalyst increase the rate of industrial chemical reactions
Lower temps required for reactions
Less electricity from combustion of fossil fuels required
Less combustion of fossil fuels so fewer emmissions of CO2 and other pollutants
Limitations of some industrial catalysts, and why they are still used
Some are toxic
Benefits outweigh risks
Examples of toxic catalysts 3
Rhodium, Palladium, platinum
