At equilibrium for the reaction H2 (g) + Br2 (g) is revesible arrow 2HBr (g) in a 10 litre vessel was found to contain 2.5 X 10 to the power -3 mole of H2 , 0.150 mole of HBr and 2.8 x 10 to the power-3 mole of BR2. What is the value of k at this temperature?