How can one tell a reaction has reached equilibrium?

1 Answer
Mar 9, 2017

Answer:

When the rate of forward reaction is equal to the rate of reverse reaction.

Explanation:

For the generalized equilibrium we have:

#A+BrightleftharpoonsC+D#

Now we have a rate forward,

#k_f[A][B]#, and a rate backwards, #k_r[C][D]#.

#k_f# and #k_r# are unspecified rate constants, whose ratio must be determined by measurement.

The condition of chemical equilibrium is reached when,

#"rate forward "-=" rate backwards"#,

i.e. #([C][D])/([A][B])=k_f/k_r=K_"eq"#.

#K_"eq"# is the thermodynamic equilibrium constant, WHICH must be measured for a given reaction, and for a given temperature. Because chemical change is conceived to continue even after equilibrium is reached, even tho #"net chemical change"# is nil, this is labelled as #"dynamic chemical equilibrium."# After equilibrium is reached, NO NET CHEMICAL CHANGE OCCURS.