Determining Activation Energy Flashcards
What reaction are we monitoring the rate of?
A clock reaction between bromate (V) ions, bromide ions, bromine and phenol
Clock reaction description
Bromide ions reacts with bromate (V) to produce bromine
Bromine is immediately reacted with fixed amount of phenol and removed, once phenol runs out then excess bromine produced can indicate end point
End point of the reaction
Bromine remains and bleaches methyl red indicator
How to keep temperatures constant?
By keeping all boiling tubes with reactants in a water bath
How can we start this reaction?
Measure our required volumes of bromide, phenol, methyl red, sulfuric acid catalyst, bromate (V) in 1 test tube (start timer once acid catalyst is added)
What are we aiming to change in this experiment?
The temperature each reaction is kept at, eg temperature of water bath of reactions
What is rate proportional to?
1/time taken for phenol to be bleached
Why can we assume rate is proportional to 1/t8me taken for bleached methyl red?
Because the concentration of phenol is kept constant so the change as it gets used up in the experiment will be the same for all experiments
So only the time taken to reach the end point is important
Plotting an Arrhenius plot
X axis: 1/T
Y axis: ln(rate)
Time taken for methyl red bleached is inversely proportional to…
The rate of reaction
Eg longer (larger) it takes, the slower (smaller) the rate of reaction
On the Arrhenius plot, ln(k) is actually shown as… and why?
Ln(rate) aka ln(1/time taken for methyl red to be bleached)
Because this is proportional to ln(k) assuming concentration of all is kept the same
Activation energy =
-gradient x gas constant (8.31)
