[chandrablue]

A 2.50L balloon at 298 K contains butane gas. at constant pressure the temp of the balloon is then lowered to 280 K what will the new level of the volume then be?

[Garneck]

p₁V₁/T₁ = p₂V₂/T₂

p₁ = p₂

V₁/T₁ = V₂/T₂
2,5/298 = V₂/280

V₂= 2,5*280/298 = 2,35 L

[pkothari13]

This law is commonly known as Charles' Law. (V₁/T₁ = V₂/T₂)

At constant Temperature, it is Boyle's Law, and at constant Volume, you use Gay-Lussac's Law.

However, as Garneck demonstrated, instead of memorizing all three of these formulas, just remember the Combined Gas Law, and proceed from there.