When hydrogen gas combines with chlorine gas...?

Question

When hydrogen gas combines with chlorine gas, a corrosive gas known as hydrogen chloride forms. According to Dalton, the volume ratio between the reactants and products should be 1:1:1. However, g*y-Lussac would claim a ratio of 1:1:2 (assuming that all gases are the same temperature and pressure). g*y-Lussac's claim was proved to be valid. Which law is being used here? Explain why this explanation works better than Dalton's.

Answer 1

Where did you read that Dalton claimed the volumes were 1:1:1?????

Answer 2

The law you are referring to is Avogadro's law.  

It says that at constant T and P the volumes of gases in a reaction are in the ratio of the moles.

H2(g) + Cl2(g) --> 2HCl(g)

Since the moles are in the ratio of 1:1:2, then according to Avogadro's law the volumes of gases are in the same ratio of

1:1:2.

Answer 3

g*y-Lussac claimed that at constant temperature and pressure, moles and volume are proportional. This can be seen from the ideal gas law. So if you react equal volumes (which is proportional to moles) of H2 and Cl2 at constant T and P, say 25 L each, by the law of conservation of mass, you'd better get 50 L of product, which is HCl alone. If volume is proportional to moles, then the H2:Cl2:HCl ratio is 1:1:2.

Dalton's problem was that he thought that hydrogen and oxygen were MONATOMIC, i.e.

H + Cl  ===>  HCl

so you see why he thought the ratio was 1:1:1.