# Do Gases Get Heavier or Lighter as Their Temperature Rise?

I know that as the temp. in gases change, their weight does, but I'm not sure in what direction.

I know that as the temp. in gases change, their weight does, but I'm not sure in what direction.

active| newest | oldestPV = nRT is the basic equation of a perfect gas.

P = pression,

V = volume,

T = temperature,

R = constant, typical of each gas,

"n" is the number of gas molecules. This is the "mass" of the matter and cannot change. Thus, in the real world, the WEIGHT cannot change, unless nuclear reactions take place, which transform mass into energy.

As others have stated, weight do not change but DENSITY changes. Density is the ratio mass / volume. Thus density will change if V change. How is the V related to T?

If temperature increases, then the product PV must increase. This can be caused by increase of P or V, or both.

If the gas is contained in a confined system (let say a closed metal bottle), then the volume cannot change and pression will increase.

If the gas is contained in a expandable system (let say a rubber baloon), then the volume can also increase and, up to a limit, pressure will increase only slightly. However, the, as the volume reaches a threshold, the baloon walls are not more elastic. At this point volume do not increase, but pression do. This happens when you inflate a tyre.

PV=NRT

L

pressureincreases with temperature (Gay-Lussac's Law). If the gas is enclosed in a fixed pressure container (like a balloon), then thevolumeincreases with temperature (Charles' Law).So why do balloons rise when you heat them? Because the

volumeincreases, so the balloon displaces more air. Since the balloon's weight remains constant, but the larger volume of air weighs more, buoyancy pushes the balloon up.