Let's put some numbers to our well example from the text. Fracking for natural gas promises to be a clean technology because we are probing so deeply for the gas. Such deep wells mean there might be a considerable difference in gas composition from the bottom to the top. The well contains methane and propane and is $2000 \mathrm{~m}$ deep. You may assume the mixture behaves ideally, but as the well gets deeper, the temperature rises, $20^{\circ} \mathrm{C}$ for every kilometer in depth. At the surface, the composition is $80 %$ methane, $20 %$ propane, and the surface temperature is $25^{\circ} \mathrm{C}$. What is the composition at the bottom of the well?