[raznoswag]

Hi, so I am trying to figure out these two problems:

1. Water boils at 100°C. Substance that is to be dried decomposes above 60°C. Calculate the maximum pressure to be used for vacuum drying that substance in order for the substance to endure the drying.

2. Gas tank has volume of 60 liters (60000cm^3). It is filled with hydrogen at 150 bar(1.5x10^7 Pa) pressure. How much energy can fuel cell produce from this hydrogen, if fuel cell reaction is H₂ -> 2H⁺ + 2e^-; fuel cell efficiency is 70%, E=1.23 V, R=8.31 Jxmol^-1xK^-1, molar volume of hydrogen is 22.4 dm³⁺xmol^-1, MH₂=2gxmol^-1 and F= 96 485 Axs mol^-1?

Thank you in advance

[Borek]

Please read the forum rules, especially the part about showing your attempts.

[Enthalpy]

1. You need either a table of vapour pressure below 100°C, or extrapolate it from 100°C, which can be done from the heat of vaporization.

2a. You're probably expected to apply the perfect gas law at 150bar, which isn't a very good idea. As a perfect gas, hydrogen would have 1/5 its liquid density, a clear hint that corrections are needed. Using a table for hydrogen density vs pressure and temperature would be better.

2b. The question mixes energies and voltages, which isn't very good. For instance, the heat of formation of H₂0 tells 1.26V rather. Anyway, you're probably expected to tinker the given moles, volts, coulombs and get an energy.