Which of the following reactions is/are spontaneous? (i) #Cl_2 + 2Br^(-) -> Br_2 + 2Cl^(-)# (ii) #Br_2 + 2I^(-) -> I_2 + 2Br^(-)#
1 Answer
Both of those reactions are spontaneous.
Explanation:
You're actually dealing with two redox reactions, which means that you can easily figure out which one, if any, is spontaneous by looking at the standard reduction potentials for the half-reactions.
Take the first reaction
The standard reduction potentials for the half-reactions are
In order for the reaction to take place, you need chlorine to oxidize the bromide anion to liquid bromime, and be reduced to the chloride anion in the process.
Since chlorine has a more positive
The standard cell potential for the overall reaction will thus be
The spontaneity of the cell is given by the equation
This basically tells you that, in order for the cell reaction to be spontaneous,
Since this is the case for the first reaction, it is indeed spontaneous.
The same approach can be used for the second reaction.
Once again, use the standard electrode potentials
This time, you need bromine to oxidize the iodide anion to iodine, and be reduced in the process. The more positive
The first equilibrium will again shift to the left, and the second equilibrium to the right. This means that you have
Again, a positive