Can the pressure or temperature of a gas or liquid have a direct influence on its volume ?

Question

Hi, hope someone can help with this basic physics question. I realise that the pressure of a liquid or gas is proportionate to changes in its volume and temperature. But does the actual volume of a gas or liquid ever change due to changes in its temperature or temperature,

Answer 1

Well I believe it is different for liquids, but for gases there is a distinct relationship. For instance, if Temperature is constant pressure and volume have an inverse relationship (i.e. if you raise the pressure it will lose volume). If Volume is constant, then changes in temperature will directly affect pressure. It is all dictated by the combined-Gas Law:

((p1v1) / T1 )= ((p2v2) / T2)

So to answer your question: Yes under some conditions there will be a direct relationship (i.e. pressure is constant, if you increase temperature, the volume will increase.). Remember this is for a gas.

Answer 2

PV = nRT; where P is pressure, V is volume, n is number of moles, R is a constant, and T is temperature in degrees Kelvin. This applies to a perfect gas (monotonic).

Assume V = constant, like a metal canister. Assume n is constant, the same number of moles. R is constant. Thus, P = KT; where K = nR/V, which is constant.

Now assume two temperatures T > t; so that P/p = KT/Kt = T/t. This gives P = (T/t) p; so we see that the pressure p varies as (T/t). For example, if T = 2t, we have P = (2t/t)p = 2 p. This means when we double the temperature at constant volume, the pressure has to double.

By similar means we can also show V = (T/t) v at P = p = constant. Which means at constant pressure, the volume increases with increasing temperature.

Now let's assume T = t = constant. From PV = nRT and pv = nRt = nRT, we see PV = pv and P = (v/V) p; so that at constant temperature, if the volume decreases (V --> v), the pressure has to rise.

The physics is in PV = nRT; learn how the variables P, V, and T vary when one of them is assumed constant.

PS: The previous answer is correct, this does not apply to liquids which are incompressable for all intents and purposes. And this give rise to Pascal's Law, which I suspect you will learn eventually.