[powerlord86]

I need to present this to my chemistry class, if you guys could take a look at it.

When going through phase changes, energy is required. Perhaps one of the best known forms of phase change is when water goes from liquid to a gas.

?H + H20(l) <--> H20(g)

This equation is actually in equilibrium, as both condensation and evaporation are happening. If there is more condensation, then the equation will shift to the right, increasing the rate of evaporation, and so forth. At equilibrium, we can determine the enthalpy of water vapor, the energy required for water to vaporize.

Whether there is more evaporation or condensation depends on the state of the molecules. The average kinetic energy of liquid molecules is a function of temperature, meaning that if the heat rises, the water molecules will move faster and thus have the energy to leave the liquid phase to the gas phase. Moreover, the pressure of the water vapor is proportional to the amount of collisions, which is dependent on the amount of molecules.

To actually determine ?H in through those relationships between the equilibrium constant (Kp) and the temperature (T) and pressure (PH20), and equation is derived from the Arrinheus equation.




(sorry the picture came out small, but it goes from Arrhenius to Kp = P h20 to the clausius equation)

The temperature (1/T = x-axis) and the pressure (ln(PH20) = y-axis) of water can be graphed, and thus: slope = -?H/RT. Thus you can solve for the enthalpy ?H.



Thanks for reading it.

[Donaldson Tan]

Your calculations assume dH to be constant. You should justify your assumption.