Mixed Gas Question 3

Question

1.The temperature inside my refrigerator is about 4^o Celsius. If I place a balloon in my fridge that initially has a temperature of 34 ^oC and a volume of 0.293 liters, what will be the volume of the balloon, in L, when it is fully cooled by my refrigerator? Answer with correct significant figures and unit in abbreviation.

2.A gas in a sealed container has a pressure of 261 kPa at a temperature of 36 °C. If the pressure in the container is changed to 101.7 kPa, what is the new temperature in °C ?  Answer with no decimal place and the unit C (without the circle for degrees).

Answer 1

Hello, Jahnine,

We can use the combined gas law: P1V1/T1 = P2V2/T2, where the subscripts are the intital (1) and final (2) states. Temperature must be in Kelvin.

We want the final volume, so rearrange:

V2 = V1(T2/T1)(P1/P2)

I've rearranged the temperature and pressure variables as ratios, to make unit cancellation easier and to help prevent errors with data calculations. It also allows us a quick glimpse into what our answer might look like. The pressure remains conastant, so (P1/P2) = 1. I like that. Plus, it tells us the we would not have to have converted pressures from, say Pa to atm, since it is only the ratio that matters.

So we are left with V2 = V1(T2/T1)

Since (T2/T1) is less than 1, we should see a volume decrease, which is what we'd expect if cooling a gas.

Covert C to K by adding 273.15 and calculate.

V2 = (0.293L)*(277.15K/307.15K)

V2 = 0.264 L

The volume decreased, as expected.

Bob