Rate Equations Flashcards
(53 cards)
Define the rate of reaction
Change in concentration per unit of time
Define activation energy
The minimum energy required for a reaction to occur
Why does a higher temperature increase the rate of reaction
More particles have more energy than activation energy, there are more frequent successful collisions so particles react
Why does a higher concentration/pressure increase the rate of reaction
More particles in the same volume, more frequent successful collisions
Why does breaking a solid into smaller powder particles increase the rate?
More surface area, more frequent successful conditions
What is a catalyst
A substance which increases the rate of a reaction
Without being used up
How does a catalyst work
Provides an alternative reaction route, with a lower activation energy
Key points for the maxwell-Boltzmann distributions
Must start at the origin-> no particles have 0 energy
The highest peak is the most probable energy
Never touches the X axis at the end
Area under the curve tells you the number of particles
What is the calculation of rate
Rate= change in concentration/ time
Why do chemical reactions start off with a fast rate and then slow down
high conc of reactants means a high rate of collisions. As reactants get used up successful collisions become less frequent, once one or more reactants are used up there are 0 successful collisions
Zero order
If changing the concentration of a reactant has no effect on the rate of reaction it is said to be zero order with respect to the rate of reaction.
For example if the concentration of A doubles, the rate remains the same
As a graph this is a horizontal line
1st order
Changing concentration is directly proportional to rate of reaction
For example if the concentration of A is doubled, the rate is also doubled
As a graph this is a vertical line
Second order
Changing the concentration increases the rate of the reaction by the square of the concentration
For example if concentration A is doubled, the rate is squared.
As a graph this starts of steep and curves
How could you express rate for X+Y—> Z
Rate= K[X][Y]2
How do you calculate the units for an order reaction
1-the overall order
Moldm-3s-1
Why would you use a large excess of reactant
Means the order of reaction is zero with respect to that reactant as the reactants concentration is effectively constant
What are the two types of experiment done to determine the order of a reaction
Continious monitoring- following the course of a single reaction
Initial rates method- doing multiple experiments
Continious monitoring method
Take samples at regular intervals by using a visible indicator such as gas volumes
What is the problem with the continious monitoring method
The reaction is still reacting- quench the reaction, add a large volume of cold distilled water, it will cool and dilute the reaction, decreasing the rate.
Monitoring using a physical property and its problem
The volume of gas produced could be measured at regular intervals
Problem- it records the product produced and the order of reaction is about reactants. Volume recorded would need converting to reactant concentration
How to measure a reaction that changes colour
Colourimetry
Draw graphs for zero, first and second order for continious monitoring method
Reference to picture on phone
How to measure the initial rate using a graph produced from the continuous monitoring method
Draw a tangent, find the gradient- this will give the rate for that specific time.
How to work out an order from a CTT graph- use the example:
Concentration went from 0.1 to 0.03. The rate changed from 2x10-4 to 6x10-5
Take two tangents at different concentrations and compare the factor of change in concentration to rates.
Conc and rate have decided by 3
Rate is proportional to change so 1st order
