Kinetics Flashcards
What does the rate of a chemical reaction depend on?
collision frequency
collision energy
activation energy
collision geometry
What is collision theory?
The number of collisions between particles per unit time in a system
How can collision frequency be changed?
The collision frequency of a given system can be altered by:
Changing the concentration of the reactants
Changing the total pressure
Changing the temperature or by changing the size of the reacting particles
Equation of the Rate of Reaction?
Change in Amount of Reactants or Products/ Time Taken
Limitations of measuring the rate of reaction during a change in mass?
However, one limitation of this method is the gas must be sufficiently dense or the change in mass is too small to measure on a 2 or 3 dp balance
What is activation energy?
For a reaction to take place, the reactant particles need to overcome a minimum amount of energy
This energy is called the activation energy (Ea)
Exothermic Diagram
Anse
Endothermic Diagram
Answer
How does Conc affect ROR
The more concentrated a solution is, the greater the number of particles in a given volume of solvent
An increase in concentration causes in an increased collision frequency and therefore an increased rate of reaction
How does Pressure affect ROR?
An increase in pressure in reactions that involve gases has the same effect as an increased concentration of solutions
When the pressure is increased, the molecules have less space in which they can move
This means that the number of effective collisions increases due to an increased collision frequency
An increase in pressure therefore increases the rate of reaction
How does Temp affect ROR?
increasing the temperature of the reaction mixture increases the rate of reaction in the following two ways:
At higher temperatures, the particles are moving faster, so collide more frequently. A higher number of collisions in total mean a higher number of successful collisions
At higher temperatures, a higher proportion of the molecules have the activation energy or more. This means that a higher proportion of collisions are successful
How does SA affect ROR?
Only the particles on the surface of a solid will collide with particles of the other reactant
If the surface area is increased, more particles will be on the surface and able to collide with particles of the other reactant
This means that there will be more collisions in total and therefore more successful collisions.
Surface area can be increased by decreasing the size of the reactant particles
For example, powders have a very large surface area
