Question

State and explain Gay Lussac’s law of combining volumes.

Answer 1

Hint: Joseph Louis Gay-Lussac began his career by very carefully showing the validity of Charle’s law for a number of different gases. Gay-Lussac's most important contribution is on the study of gases, however, most of the experiments he performed were on the ratio of the volumes of gases involved in a chemical reaction.

Complete step by step solution:
Let’s begin with the definition of the Law of combining volumes:
The law of combining volumes by Gay-Lussac states that, when different gases react together, they do so in terms of volume which bears simple whole-number ratio provided that the temperature and pressure of reacting gases remain constant. In other words, the ratio of the volumes of the gases in the reactant and the gaseous products can be expressed in simple whole numbers.
The above definition is a bit confusing so let’s take an example to make it clear.
 \[{H_2}\left( g \right){\text{ }} + {\text{ }}C{l_2}\left( g \right) \to 2HCl\]
If we take two volumes of hydrogen and one volume of chlorine, both would react with each other to form two volumes of hydrogen chloride. Based on Gay-Lussac's results, Avogadro gave his hypotheses that, at the same pressure and temperature, equal volumes of gas contain equal numbers of molecules (Avogadro’s Law). This hypothesis meant that the result which was stated previously i.e.
2 molecules of hydrogen + 1 molecule of chlorine = 2 molecules of hydrogen chloride.
Could also be expressed as
2 molecules of hydrogen + 1 molecule of chlorine= 2 molecules of hydrogen chloride
It can also be expressed in a different way, for example, consider 100 mL of hydrogen combined with 100 mL of chlorine to give 200 mL of hydrogen chloride.
Hydrogen (100 mL) + Chlorine (100 mL) = Hydrogen Chloride (200 mL)
Thus, the volumes of hydrogen and chlorine which combine (i.e., 100mL and 100mL) bear a simple ratio of 1:1 and thus the simple ratio volumes are 1:1:2.

Note: Gay-Lussac has given many different laws like Law of combining volumes in which pressure and temperature are constant whereas in Pressure-Temperature law the number of molecules and volume remains constant. You have to carefully consider the laws and most importantly what you have to keep constant.