Charles' Law

V is proportional to T ( P, n constant) V₁T₂ = V₂T₁

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Gay -Lussac's Law of Combining Gas Volumes

When measured at the same pressure and temperature, the volume of a gas reactants and products are in ratios of simple whole numbers.

H2(g)	+ Cl2(g)	--> 2 HCl(g)	stoich ratio ,volume ratio
2.5 L	2.5 L	5.0 L	1:1:2, 1:1:2
3 H2(g)	+ N2(g)	---> 2NH3(g)	stoich ratio ,volume ratio
7.5 L	2.5 L	5.0 L	3:1:2, 3:1:2

Why do gases combine in simple whole numbers? Because when gases react the molecules react in simple whole numbers.

6 molecules of H₂ react with 6 molecules of Cl₂ to produce 12 molecules of HCl. You cannot have half a molecule reacting or two-thirds of a molecule reacting.