Unit 3 - Reaction Rates Flashcards
What does the steepness of the reaction curve tell us about the reaction rate?
How fast the reaction is proceeding.
What is the equation for reaction rate?
reaction rate = change in quantity/change in time
What is the equation for the relative rate of a reaction?
Relative rate = 1/t
When do reactions take place?
When there are SUCCESSFUL COLLISIONS between reactants.
How can you speed up a reaction?
Decreasing the PARTICLE SIZE of any solid. (Increased surface area = increase in the probability of SUCCESSFUL COLLISIONS).
Increasing the CONCENTRATION of a solution. (Increasing the NUMBER OF PARTICLES = increase in the probability of SUCCESSFUL COLLISIONS.)
Increasing the TEMPERATURE of the reaction.
(Increases the amount of energy and the speed of particles = increase in the probability of SUCCESSFUL COLLISIONS.)
Using a Catalyst. (Increases the probability of SUCCESSFUL COLLISIONS.) (Is not used up and can be used again)
What do all molecules and atoms have?
Kinetic energy in the form of vibrations,
What does collision theory state must happen for a reaction to take place?
Collision theory states that in order for a reaction to take place the particles in the reactants must collide.
What molecules will collide successfully in collision theory?
Molecules with more energy than the activation energy that collide in the correct orientation and geometry
How can sufficient energy for successful collisions be achieved?
With an increase in temperature the molecules will gain kinetic energy, and more molecules will have the required energy to collide successfully and to react.
What is the activation energy?
The activation energy is the minimum energy required by colliding particles to form an activated complex.
In exothermic reactions what is the ΔH?
Negative
In endothermic reactions what is the ΔH?
Positive
What is enthalpy?
A measure of the change in potential energy between the reactants and the products of a reaction.
Unless stated on the graph what is enthalpy measured in?
kJmol-1
What is an exothermic reaction?
An exothermic reaction involves the reaction RELEASING energy to the surroundings, usually in the form of heat.
What is an endothermic reaction?
An endothermic reaction ABSORBS energy (usually in the form of heat) form the surroundings.
What does ‘ whether a reaction is fast or slow ‘ depend on?
The height of the activation energy barrier.
What does a catalyst provide?
A catalyst provides an alternative reaction pathway with a lower activation energy but does not have an effect on ΔH.
Is the reaction rate slower for a reaction with a higher activation energy?
Yes
Is the reaction rate slower for a reaction with a lower activation energy?
No
What is the activated complex?
The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction. They are very short lived and have bonds being broken and made at the same time.
What happens in regards to activation energy when a catalyst is added?
The activation energy decreases.
What are the two types of catalysts?
Heterogeneous and homogeneous.
What is a homogeneous catalyst?
A catalyst which is in a different state as the reactants.
What is a homogeneous catalyst?
A catalyst which is in the same state as the reactants
What is adsorption in catalysis?
Occurs when molecules attach themselves to the catalyst
What is desorption in catalysts?
Occurs when the molecules leave the surface of the catalyst
What is catalyst poisoning?
Where IMPURITIES PERMANENTLY BLOCK the active site decreasing the efficiency of the catalyst.
How do catalysts actually speed up the reaction?
As the molecules are held in a fixed position by the catalyst it is easier for the molecules to collide/there is a higher chance of the molecules colliding.
