To determine how a decrease in temperature affects the equilibrium constant Kc for the reaction N2 g + 3H2 g 2NH3 g , we need to consider the reaction's enthalpy change H . The formation of ammonia NH3 from nitrogen N2 and hydrogen H2 is an exothermic reaction, meaning it releases heat H < 0 .According to Le Chatelier's principle, if a system at equilibrium is subjected to a change in temperature, the system will adjust itself to counteract the change. In this case, since the reaction is exothermic, a decrease in temperature will shift the equilibrium to the right toward the formation of NH3 to produce more heat. As a result, the equilibrium constant Kc will increase.To calculate the new equilibrium constant at 250C, we can use the van't Hoff equation:ln Kc2/Kc1 = -H/R * 1/T2 - 1/T1 where Kc1 and Kc2 are the equilibrium constants at temperatures T1 and T2, respectively, H is the enthalpy change of the reaction, and R is the gas constant 8.314 J/molK .However, we do not have the value of H for this reaction. Without this information, we cannot directly calculate the new equilibrium constant at 250C. But we can qualitatively say that the new Kc will be greater than the initial Kc 4.34 x 10^-3 due to the decrease in temperature for this exothermic reaction.