Physical - Rate Equations Flashcards
What is the rate equal to?
The rate constant (k) multiplied by the concentration of each reactant raised a certain whole number powers
What does it mean if reactant is zero order?
Some reactants may be zero order, which means they do not appear in the rate equation as [X]^0 = 1
What is the rate equation for a general reaction?
Rate = k[A]^m[B]^n
m is the order of reaction with respect to reactant A.
n is the order of reaction with respect to reactant B.
What does it mean if the order with respect to a reactant is 0?
If the concentration of a reactant changes and the rate stays the same.
So if [A] doubles the rate will stay the same. If [A] triple the rate will stay the same.
What does it mean if the order with respect to a reactant is 1?
The rate is proportional to the concentration of a reactant.
So if [A] doubles the rate will double. If [A] triple the rate will triple
What does it mean if the order with respect to a reactant is 2?
If the rate is proportional to the concentration of a reactant squared.
So if [A] doubles the rate will be 2^2=4 times faster. If [A] triples the rate will be 3^2=9 times faster
How does temperature affect the rate constant?
1) As the temperature increases, the rate constant increases.
2) The rate constant increases exponentially as temperature increases.
3) A graph of the rate constant (k) against temperature (measure in K)
What is the Arrhenius equation?
The Arrhenius equation links the rate constant with activation energy and temperature
What is the Arrhenius equation?
k = Ae^-Ea/RT
- k is the rate constant
- A is the Arrhenius constant
- e is a mathematical constant (e^1 on calculator)
- Ea is the activation energy
- R is the gas constant
- T is the temperature measured in K
What are the four methods for determining the rate of reaction?
1) A gaseous product which can be monitored using a gas syringe or by loss in mass.
2) A coloured reactant or product which can monitor using colorimetry
3) A directly measurable reactant or product ie. H+ ions or OH- ions by measuring pH using A pH meter.
4) A titratable reactant or product which can be monitored by sampling, quenching and titrating.
What is the rate determining step?
The right determining step is the slowest step and it dictates the overall rate of the reaction.
The species that react in the rate determining step are the species which are present as concentrations with non-zero orders in the rate equation.
Reactants in the overall equation which have zero order are not involved in the rate determining step
What is the order of a reaction?
The order of reaction to a particular reactant is the power to which the concentration of this reactant is raised in the rate equation.
What is the overall order of the reaction?
The overall order of the reaction is the sum of all the orders in the rate equation. In the general example it would m+n
What is the rate constant?
The rate constant is the proportionality constant which links the rate of reaction to the concentrations in the rate equation.
How is rate of reaction measured using a gas syringe?
A gas syringe is a ground glass syringe which is attached to a sealed reaction vessel and measures the volume of gas produced. This is measured against time and a graph of gas volume against time is plotted. The gradient of the tangent at t=0 gives the initial rate of reaction.
How is rate of reaction measured by measuring change in mass?
A reaction in which a gas is produced may also be monitored by measuring the mass over a period of time. The curve of the graph decreases again and initial tangent at t=0 seconds gives a measure of the initial rate of reaction.
How is rate of reaction measured by measuring a coloured reactant or product?
A colorimeter measures the colour intensity of a solution. For example, if you are measuring the intensity of a blue solution, you should use a red filter as the solution is absorbing red light. The amount of red light absorbed relates directly to the concentration. A calibration curve should be set up first with known concentrations of the reactant or product so that you directly relate the colorimeter reading to the concentration.
How is rate of reaction measured by measuring a reactant or product by titration?
Sampling, quenching and titrating allows a titratable reactant or product to be measured during the course of the reaction. A sample of taken at various times, and the reaction is quenched (stopped). The sample may then be titrated to find the concentration of the reactant or product.
What does the zero order graph look like?
Straight horizontal line
What does the first order graph look like?
Straight positive correlation line
What does the second order graph look like?
Curved positive correlation line
