Question

Law of definite proportions when expressed in terms of volume becomes:
A. Dalton’s Law
B. Berzelius hypothesis
C. Gay-Lussac’s Law
D. Avogardo’s Law

Answer 1

Hint: The law of definite proportions can be used alternatively in a different manner, where the volume of the gases present are considered, instead of the combining fixed masses of the respective elements.



Complete answer:
-In order to answer our question, let us learn about the law of definite proportion. According to the law, ‘a chemical compound always contains exactly the same proportion of elements by mass’. Thus, irrespective of the source, a chemical compound always contains the elements in fixed ratio by mass. For example, carbon dioxide can be obtained by different methods like burning of carbon, heating limestone and action of hydrochloric acid on marble pieces. All these different samples of carbon dioxide contain carbon and oxygen in the ratio 3:8 by mass.
-However, in Gay-Lussac’s Law, it is stated that ‘when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure. It has been found that one volume of nitrogen combines with three volumes of hydrogen to form to volume of ammonia as. We can represent the reaction as: $3H_2(g)+N_2(g)->2N{H}_3(g)$
-Therefore, the ratio by volumes of nitrogen, hydrogen and ammonia is 1:3:2 which is a simple whole number ratio. Gay-Lussac’s discovery of integer ratio in volume relationship is in fact the law of definite proportions by volume. However, the law of definite proportions was with respect to masses of the substances. The Gay-Lussac’s Law was carefully explained in the year 1811, by the work of Avogardo.

Note: It is to be noted that in Avogadro's Law, the condition imposed is that gases need to have the same temperature and pressure, which is the same as Berzelius hypothesis. However, in the latter part, equal volumes of gases are said to have equal numbers of atoms.