Kinetics Flashcards
3 reasons for knowledge of rates of reactions
Can sped up or slow down a reaction in the laboratory
Can choose optimum conditions for reaction
Gives us information on how a reaction takes place
What are the five main factor that affect how fast a chemical reaction takes place?
Temperature, concentration, pressure, surface area and catalysts
Do the factors affecting the rate of chemical reaction affect the number or collisions involving reacting particles or activation energy?
Temperature both Concentration collisions Pressure collisions Surface area collisions Catalyst both
What are the two things particles need to react?
Activation energy
Correct orientation
What is the difference between a homogeneous and heterogeneous reaction?
Homogeneous- reactants are in the same phase
Heterogeneous- reactants are in different phases
What is the definition of a catalyst?
A substance that changes the rate of a chemical reaction without being used up or undergoing any permanent chemical change
why are catalysts so useful in the chemical industry?
Enable a profitable reaction without resorting to excessive and expensive conditions of temperature and pressure
What does the rate of reaction describe?
The rate at which the reactants are used up and the products formed
What is the equation for calculating the rate of reaction?
Change in x/ time
Why is it more accurate to comparing Initial rate of reaction when comparing rates?
Because the rate changes as the reaction proceeds along with the amounts of reactants
What are two ways of monitoring the rate of reaction when a gas is given off?
Record the change in mass of the mixture
Record the volume of carbon dioxide gas given off
Why does starch turn blue black in the presence of iodine?
It forms a complex
When doing titrimetric analysis:
What is an aliquot?
What is quenching?
Why is the mixture quenched?
A small portion of the reaction mixture
Stopping the reaction
To prevent the reaction going any further until analysis can be carried out
What is the name of the equipment that can quantitively measure the colour change during a reaction?
Photoelectric colorimeter
What needs to happen to allow conductimetric Analysis to be carried out?
A change in the number of ions present
What does the rate of reaction measure in terms of collisions?
How frequently effective collisions occur
What is the definition of activation energy? What is the symbol?
The minimum amount of energy required to start a reaction by breaking bonds
Ea
What causes particles without activation energy to simply bounce off each other?
The repulsion between their negative electrons clouds
What happens during an unsuccessful collision between reactant particles?
Particles move towards each other, slow down, stop, then fly apart again unchanged
What happens to the kinetic energy of particles as they come together?
It goes down and is transformed into potential energy
What happens on exothermic reaction profile?
Ea- reactant molecules are coming together and bonds are breaking apart. Energy is being absorbed
Product molecules are forming and moving away from each other. Energy is being released
What property of the reacting particles determines whether the activation energy will be met or not?
The combined initial kinetic energies of the colliding particles
What happens during a reaction with a catalyst?
Particles come together and bonds start to break
Activated complex forms
Activated complex bonds break
Product molecules form and move apart
What is the definition of an activated complex?
A transitional structure in a chemical reaction that results from an effective collisions between molecules and that persists while old bonds are breaking in new bonds are forming
Do you all particles in a reaction mixture have the same amount of chemical energy?
No
What is the Mazwell-Boltzmann model?
A model for expressing the distribution of energy among the molecules of a gas in thermal equilibrium
What does the area under a graph in a Maxwell Boltzmann model represent?
The total number of particles
What does the peak on a Maxwell Boltzmann model represent?
The average speed of the particles
How does a catalyst speed up the reaction?
Catalyst provides an alternative route/mechanism (1)
with lower activation energy
ALLOW low activation energy (1)
So a higher proportion (ALLOW more) molecules / collisions (ALLOW reactants) have energy equal to or greater than Ea