A mixture of is held in a 1.0-L vessel at 90C until the following equilibrium is a...

A mixture of is held in a 1.0-L vessel at 90C until the following equilibrium is achieved:

At equilibrium the mixture contains 0.46 g of H₂S and 0.40 g H₂. (a) Write the equilibrium-constant expression for this reaction. (b) What is the value of Kc for the reaction at this temperature? (c) Why can we ignore the amount of S when doing the calculation in part (b)?