For which gases does the ratio of pv to rt equal a constant? ideal gases gases at very high pressure gases of very low temperature real gases

It's one for ideal gases . by the way , remember that it's molar volume not volume itself and, this ratio is shown by Z and is called Compressibility factor.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.