mixture thermodynamics

In the previous post, we saw how to calculate the speed of sound of a mixture of ideal gases, the main assumption is that we can add the individual specific heats of the components, weighted by the mass fractions.

This is exercise 13-97 from [1]: a mixture of gases composed of 55% of nitrogen gas and 45% of carbon dioxide (in mass) is originally at 200 kPa and 45 ˚C.

In a previous post, we performed a First-Law Analysis, calculating work and heat transfer, of a mixture of ideal gases. Now we have a more realistic situation, taken from Exercise 13-99 from [1]: a mixture of 4 kg of \(\mathrm{He}\) and 8 kg of \(\mathrm{O_2}\) is kept in a rigid tank initially at 170 K and 7 MPa and pressure.

Why do we need a separate mixture thermodynamics subject? Because, when two fluids are mixed, the individual properties do not necessarily add up to the total system, due to interaction effects.