Rate, Orders and Arrhenius Flashcards
What is half life?
The time is takes for half of a reactant to react/concentration of a reactant to half.
What does the rate equation show us?
Exactly how each reactant changes the rate of a reaction.
How can pH be used to measure rate of reaction?
Using a pH meter to measure pH at regular intervals then finding [H+] from it.
How is a colorimeter used to measure rate of reaction?
It measures the absorbance of light by a coloured sample. The darker, the more absorbance.
Eg, Iodine (brown) and propane (colourless) making CH3COOH2I-(aq) + I-(aq) + H+(aq) which is colourless.
Plot a calibration curve of known idodine concentrations against light absorbance and plot the results at each con.
What does the iodine clock reaction do?
Investigating the effect of concentration on reaction rate.
How does an iodine clock reaction work?
It uses the reaction between hydrogen peroxide and iodine
H2O2 (aq) + 2I- (aq) + 2H+(aq) → I2 (aq) + 2H2O (l)
Sodium thiosulfate is added, acting as a timer by using up the iodine.
There are 2 reactions occurring simultaneously, one affecting the other.
S2O82- (peroxidised sulphate ions) + 2I+ —> 2SO42- + I2 (reddy brown). This is slow
The solution goes from clear to reddy brown.
Step 2:
I2 + 2S2O32- —> 2I- + S4O62-
(iodine from first step + thiosulphate make iodide.)
This is a fast reaction.
Starch is also added (blue black in iodine). This makes it obvious when the change occurs.
1.There is more peroxidised sulphate than thiosulfate so…
The top continues creating iodine and the 2nd step stops once thiosulfate runs out. As a result the solution turns blue/black.
How do you use the results of the iodine clock reaction to find the rate of reaction?
As we know the concentration of thiosulfate in the 2nd step, we can find how much idodine has been made via step one, and how much iodide and peroxidised sulphate has been used.
Divide the amount of iodine made by the total volume of solution, then divide by time it took to go black.
AKA, find concentration of iodine, then divide by time.
If one mole of thiosulfate is added to an iodine clock reaction, what are the moles of other reactants and products?
If we use 1 mol of thiosulfate, the moment it turns black means 1 mol of thiosulfate has been used up, 0.5 mol of peroxidised sulphate ions were used up and 0.5 mol of iodine has been used and created.
What is 0 order reactant?
When change in reactant concentration doesnt affect rate of reaction.
What is 1st order reactant?
When change in rate is directly proportional to increase in reactant con.
Eg, double the reactant concentration doubles rate of reaction.
What is a 2nd order reactant?
When a reactant concentration is increased by a factor so the rate increases by the aqare of that factor.
Eg: 2x reactant = 2^2 rate.
3x reactant = 3^3
What is overall order?
The sum of all the orders of a reaction.
eg 1st order and 2nd order = 3.
What is the rate equation?
rate = k[A]^a[B]^b
overall rate = a+b
rate =moldm-3 s-1
What is the rate constant?
K, in the rate equation. It contains everything else to do with rate, temp, Ea, orientation, pressure.
This means even if the concentrations are high the rate of the reaction may be low if there is a low rate constant.
How do you determine the order of a reaction?
Graphs or tables.
In graphs rate is plotted against concentration or time.
