posted by trigger .
Ammonia reacts with oxygen in the presence of a platinum catalyst to give nitric oxide and water, according to the following gas phase equilibrium:
4NH_3(g) + 5O_2(g) <---> 4NO(g) + 6H_2O(g) ÄH = −906 kJ mol^−1
What is an appropriate equilibrium expression for the reaction. What would the units of the equilibrium constant K be if the concentrations of all the gases in the equilibrium expression were measured in mol dm−3? And how do you determined your units for K using your equation.
Isn't this just the standard Keq expression? What's not to understand?
As far as the units, put the ones suggested into the equation and see what dimensional analysis gives you. Technically, the Keq has no unit since activities go into the calculation of Keq and activities have no units. However, problems use molarities, in most cases, and they often ask for provisional Keq in those cases.