sh the same weight of acid?

8. 100 l. of nitrogen peroxide were dissolved in water and neutralized
with sodium hydroxide. What substances were formed and how much of
each?(1 l. nitrogen peroxide weighs 2.05 grams.)

9. How many liters of nitrous oxide, measured under standard conditions,
can be prepared from 10 g. of ammonium nitrate?

10. What weight of copper is necessary to prepare 50 l. of nitric oxide
under standard conditions?

11. (a) Calculate the percentage composition of the oxides of
nitrogen. (b) What important law does this series of substances
illustrate?

12. Write the equations representing the reactions between ammonium
hydroxide, and sulphuric acid and nitric acid respectively, in
accordance with the theory of electrolytic dissociation.

13. In the same way, write the equations representing the reactions
between nitric acid and each of the following bases: NaOH, KOH,
NH_{4}OH, Ca(OH)_{2}.

CHAPTER XIII

REVERSIBLE REACTIONS AND CHEMICAL EQUILIBRIUM

~Reversible reactions.~ The reactions so far considered have been
represented as continuing, when once started, until one or the other
substance taking part in the reaction has been used up. In some
reactions this is not the case. For example, we have seen that when
steam is passed over hot iron the reaction is represented by the
equation

3Fe + 4H_{2}O = Fe_{3}O_{4} + 8H.

On the other hand, when hydrogen is passed over hot iron oxide the
reverse reaction takes place:

Fe_{3}O_{4} +8H = 3Fe + 4H_{2}O.

The reaction can therefore go in either direction, depending upon the
conditions of the experiment. Such a reaction is called a _reversible
reaction_. It is represented by an equation with double arrows in place
of the equality sign, thus:

3Fe + 4H_{2}O <--> Fe_{3}O_{4} + 8H.

In a similar way, the equation

N + 3H <--> NH_{3}

expresses the fact that under some conditions nitrogen may unite with
hydrogen to form ammonia, while under other conditions ammonia
decomposes into nitrogen and hydrogen.

The conversion of oxygen into ozone is also reversible and may be
represented thus:

oxygen <--> ozone.

~Chemical equilibrium.~ Reversible reactions do not usually go on to
completion in one direction unless the conditions under which the
reaction takes place are very carefully chosen. Thus, if iron and steam
are confined in a heated tube, the steam acts upon the iron, producing
iron oxide and hydrogen. Bu