Why Does Enthalpy of Saturated Vapour Increase with Temperature?

[r.physics]

Homework Statement

I have the ammonia liquid-vapour tables and I have noticed that the enthalpy of a saturated vapour increases as temperature increases. Can someone please help me to understand why this is the case?

Homework Equations

H = U + pV

The Attempt at a Solution

I assume that at higher temperatures the vapour will have a greater internal energy. Is this why enthalpy increases with temperature?

Thanks!

 

[Chestermiller]

Homework Statement

I have the ammonia liquid-vapour tables and I have noticed that the enthalpy of a saturated vapour increases as temperature increases. Can someone please help me to understand why this is the case?

Homework Equations

H = U + pV

The Attempt at a Solution

I assume that at higher temperatures the vapour will have a greater internal energy. Is this why enthalpy increases with temperature?

Thanks!

It also has a higher PV, since PV=nRT. So, both U and PV are higher.

Also, this is not the case at all temperatures. The enthalpy of the saturated liquid always increases with temperature, but the heat of vaporization decreases as the critical point is approached. So, at temperatures and pressures approaching the critical, the enthalpy of the saturated vapor actually decreases with temperature (i.e., along the saturation line).