Controlling the Rate Flashcards
What will happen if the rate is too low?
The process will not be economically viable
What will happen is the rate is too high?
The process might not be safe - there is a risk of explosion
What are the 3 things that need to happen for a chemical reaction to occur?
- The reacting particles must collide
- Collisions must have sufficient energy
- The reacting particles must have the correct orientation or collision geometry
What is activation energy?
The minimum kinetic energy required for a chemical reaction to occur
How is an activated complex formed?
When reactant particles collide with the required activation energy
What is an activated complex?
A high energy, unstable intermediate
How does particle size affect the rate of reaction?
Decreasing the particle size will increase the rate of reaction because the surface area of reactant molecules would increase
An increase in surface area means there is more area for collisions to occur, therefore there is a greater chance of successful collisions occurring.
The smaller the particle size, the faster the reaction
How does concentration affect the rate of reaction?
The higher the concentration of reactants, the faster the reaction.
This is because a highly concentrated reaction will have more reacting particles, meaning there are more particles which can potentially collide with each other.
Therefore, there is a greater chance of successful collisions, and so the higher the concentration the faster the reaction.
What is enthalpy?
The heat energy stored in a substance
What is enthalpy change?
The difference between the enthalpy of products and reactants, it is measured in kJmol^-1
How is enthalpy change measured?
△H = H products - H reactants
What will the △H of an endothermic reaction always be?
Positive - the energy of the products is more than the energy of reactants
What will the △H of an exothermic reaction always be?
Negative - the energy of the products is less than the energy of the reactants
What does a catalyst do?
Provides an alternative pathway for the reaction with a lower activation energy, speeding up the reaction
What effect does a catalyst have on the enthalpy change?
It has no effect
What is the relative rate formula?
reaction rate = 1/t
(units are in s^-1)
How do you work out the time from the relative rate formula?
Time = 1/reaction rate
What effect does increasing pressure have on the rate of the reaction?
Increasing the pressure increases the rate because the particles have less space to move so there is a greater chance for collisions to occur.
What is temperature a measure of?
The average kinetic energy of all particles
What effect does increasing temperature have on the rate of reaction?
Increasing the temperature increases the rete because as we increase the temp, we increase the energy the particles have which cause the collision which occur to have the energy required to react.
(more particles will have energy equal to or greater than the activation energy)
How does increasing temperature look on a potential energy diagram?
If we increase the temperature, the graph moves to the right and gets lower
