126 THE THEORY OF IONIZATIONthat part of the circuit. The passage of Zn++ ions through the
porous wall in one direction and of SO 4 ions in the other direc-
tion comprise the current in that part of the circuit.
PROBLEMS
If an electric current is passed through each of the following
cells, state observations and write electrochemical reactions for
both the anode and the cathode.
- Dilute silver nitrate with silver electrodes.
- Dilute sulphuric acid with copper electrodes.
- Dilute sulphuric acid with platinum (unattackable)
electrodes. - A current of 0.5 ampere passes between silver eleo
trodes in a silver nitrate solution for 2 hours. What is the
change of weight of the anode and of the cathode? (1 ampere
= 1 coulomb per second.)
LAW OF MOLECULAR CONCENTRATION
The treatment of equilibrium in the preceding pages has been
qualitative, having been based on the obvious principle that the
tendency of a reversible reaction, say
A + B;=±C + D
to proceed to the right is determined by the concentrations of A
and B, whereas the tendency to proceed to the left is determined by
the concentrations of C and D and that equilibrium is reached
when the effects of these two opposing changes exactly nullify
each other.
A fairly exact quantitative relationship exists among the con-
centrations of all the components of a reversible reaction when
this reaction is at equilibrium; this is known as the law of molec-
ular concentrations, and may be stated as follows: when a reversi-
ble reaction has reached a state of equilibrium, the product of the
molecular concentrations of all the components on one side of
the reaction bears a definite numerical ratio to the product of
the molecular concentrations of all the components on the other
side of the reaction. This ratio is known as the equilibrium con-
stant of the reaction, and it is always the same at the same
temperature although it may have different values at other