1.9- Rate equations Flashcards
What is the formula for the rate equation of the following reaction
aA +bB
r = [A]^m x [B]^n
What do the reaction orders mean
0, this means that the reaction is zero order with respect to that reactant
1, means if is first order multiplier
2, means that it is a second order multiplier
What is the unit for rate
mol dm-3 s-1
What are the units for K for each order of reaction
For a 1st order reaction the unit of k is s-1
For a 2nd order reaction the unit of k is mol-1 dm3 s-1
For a 3rd order overall reaction the unit of k is mol-2 dm6 s-1
Give 3 features about the rate constant
. The units of k depend of the overall order of the reaction, it must be worked out form the rate equation
. The value of k is independednt of concentration and time it is constant and at a fixed temperature
. The value of k refers to a specific temperature and it increases if we increase temperature
What is continous monitoring
. When there is an experiement over time recording the change in concentration it is called continous rate method
. The gradient represents the rate of reaction, it is fastest at the start where the gradient is steepest, and the rate then drops when the reactants get used up and the concentration drops
. The graph will eventually become hortizontal and the gradient becomes zero which represents the reaction having stopped
What happens to the rate when there is a large excess of reactants
If the concentration of one of the reactions is kept in a large excess then it will not appear to effect rate and will be pseudo zero order. This is because its concentration remains constant and does not effect rate
Give different comparisons of continous rate curves
The higher the concentration/temperature/surface area, the faster the rate will be aka steeper gradient
Different volumes of the same intial concentrations will have the same intial rates but will then end up in different amounts
What is the intial rate method
The intial rate can be calculated by taking gradient of a continouse monitioring conc vs time graph at time = 0
What is the intial rate method
The intial rate can be calculated by taking gradient of a continouse monitioring conc vs time graph at time = 0
What is a clock reaction
. In a clock reaction there are 2 successive reaction, the end point is achieved when one limited reactant runs out resulting in a sudden colour change
. By repeating the experiment several times, varying the concentration of the reactant (keep other reactants at a constant concentration) you can determine the order of reaction with respect to that reactant
. Initial rate of reaction can be represented as 1/t
Give the equations for the clock reaction for hydrogen peroxide and iodine, and explain the method
H202 +2H+ 2I- > I2 +2H20
2S2O3-2 + I2 > 2I- + S4O62-
. When the I2 produced has reacted with all of the limited amount of thiosulfate ions present
.excess I2 remains in solution
. the reaction with starch then forms black blue colour
. Repeat experiment with different concentrations of iodine ions while keeping other conc the same
. Measure the time taken for the mixture to turn blue
Effect of temperature on the rate constant (arhenius equation)
Increasing temperature increases the rate constant k, the relationship is given by the arhenius equation where A is the arhenius constan.
How do you calculate the activation energy graphically from experimental data
Use the rearraagned version of the arhenius equation, k is proportional to the rate of the reaction so the lnk can be replaced by lnrate, from plotting a graph of lnrate or lnk against 1/T the activation energy can be caculated from measuring the gradient of the line
What is the rate determining step
The rds is te slowest step that controls the overall rate of the reaction, only the reactants and products that are contained before or in the rds are in the rate equation
