so confused. I used the steps for ideal gas law, but got the wrong answer.

Question

A latex balloon will adjust to maintain the same pressure. If the balloon is filled with 29.5 L of helium initially at 23.2 degrees Celcius, what would the volume be if the temperature adjusted to -1.70 degrees Celcius?

Answer 1

Of course, the Ideal Gas Law is PV = nRT but applied to a closed system it becomes:

P₁V₁/T₁ = P₂V₂/T₂

And, in this case, since pressure is constant, it becomes even simpler:

V₁/T₁ = V₂/T₂

We are looking for V₂, so solving for V₂ we get:

T₂V₁/T₁ = V₂

The place where people sometimes make a mistake is that you MUST use absolute temperature (Kelvin) and NOT degrees C. To convert °C to K, you add 273.15 to °C so T₁ = 23.2 + 273.15 = 296.35 K and T₂ = -1.70 + 273.15 = 271.45 K. Plugging in the numbers:

V₂ = T₂V₁/T₁

V₂ = (271.45)(29.5)/296.35

V₂ = 27.0 L