# Which molecules will move faster?

1. Feb 10, 2016

### holydog23

In class today, we were talking about the Kinetic Molecular Theory and the combined gas law. I was understanding everything until our teacher threw in a question that confused me really bad

Suppose we fill two balloons with Helium gas. One of them is filled 5 liters of He and the other to 10 Liters. The molecules of which balloon will move faster?

He didn't mention anything about the temperature, so I'm assuming constant temperature here because inflating balloons doesn't change temperature. Nevertheless, this question has my head spinning; a detailed explanation would be appreciated

2. Feb 10, 2016

### Bystander

3. Feb 10, 2016

### holydog23

Well I postulated that the molecules in both balloons would move at the same speed; this is because according to the KMT, Kinetic Energy of gas particles is dependent only on temperature, so they should be at the same speed. But because of Gay-lussac's law, Volume is directly proportional to temperature, so if the volume increases, the temperature should increase and thus make the molecules within the 10 L faster. But this contradicts the KMT since it states that KE of these molecules is dependent ONLY on temperature

4. Feb 10, 2016

### Bystander

PV = RT, or PV = nRT?