Re: Determination of activation energy for the reaction between bromide and bro

This experiment having the main reaction:
5Br- (aq) + BrO3- (aq) + 6H+ --> 3Br2 (aq) + 3H2O (l)

One of the tubes contains the Br- and the BrO3- while the other tube 
containing sulfuric acid, will supply the H+.  Thus the sulfuric acid is 
one of the chief reactants, not a catalyst as you had asked.  The 
definition of a catalyst is a substance that increases the reaction rate 
of a reaction without participating in the reaction.  This reactions 
requires no catalyst as it takes place very fast.

Once the tubes are mixed, the reaction proceeds to the right.  The Br2 
produced reacts instantly with the phenol.  As soon as the Br2 is produced 
from the first reaction, it immediately becomes a reactant in the 
following reaction:

3Br2 + phenol --> tribromophenol

Since is takes 3 moles of bromine to react with one mole of phenol to 
produce one mole of tribromophenol, you can measure the reaction rate 
accurately.  When you measure the time you are finding the amount of time 
to produce 3 moles of bromine.  The indicator tells you when 3 moles of 
bromine are produced because it changes color when the second reaction is 
complete.  How does it know it is complete?  Because there is more bromine 
produced than there is phenol to react with it.  Therefore as soon as 
the second reaction is completed, the bromine left over reacts with the 
indicator and changes it's color.  So, the indicator just tells you, "O.K. 
3 moles of bromine have been made"

    The activation energy is the minimum amount of energy that the 
reacting molecules must possess before the reaction will proceed.  It is 
expressed as an amount of heat per amount of reactant (Ex/ kJ/mol).  As 
far as the thermodynamic sign, the convention really isn't agreed upon.  
Heat is heat and although you can't have negative heat, the sign of energy 
is usually used to indicate its movement.  For example, most people use a 
positive sign to indicate that an entity 'takes in heat'.  This is always 
the case for 'activation energy'.  You see, reactants aren't going to have 
to give off heat before a reaction will proceed, they will need heat.  A 
different type of energy is the heat of reaction.  This is different than 
the activation energy.  If a reaction requires additional energy after it 
has started in order to proceed, it is termed 'endothermic' and the heat 
has a positive sign again because heat must be put into the reaction.  
However, many reaction are 'exothermic' meaning that they give off heat as 
they proceed, in this instance the heat energy has a minus (-) sign 
because the reaction is giving heat to the environment.  Another thing 
worth mentioning is that in an industrial setting, most exothermic 
reactions must have the heat that they are producing carried away from the 
reactor because (as you saw in your experiment), additional heat will make 
the reaction proceed faster (in most cases).  If this heat isn't taken 
away and builds up, the reaction can reach a point called "runaway" where 
the temperatures become dangerously high and the reactor may explode.  The 
heat carried from the reactor is used to produce steam from water (which 
can be used to make electricity for the plant) or it can be used to heat 
another stream that needs heat.  

WOW, hope that helps!

Chris