The general condition for material equilibrium in a closed system capable of P-V work only is: an = 0 where is the chemical potential of substance i in the phase a, and is the small change in the quantity of substance i in the a phase. a) Write the corresponding equation for phase equilibrium, and write a sentence that describes what the equation means b) Write the corresponding equation for reaction equilibriun, and write a sentence that describes what the equation means. c) Write the equilibrium condition for the following chemical reaction: CH4 (9) +202 (g) CO2 (g) + 2H20 (9)