Can a closed system have a physical change or chemical change or both

Consider the reaction: n2(g) + o2(g) ? 2no(g) kc = 0.10 at 2000oc starting with initial concentrations of 0.040 mol/l of n2 and 0.040 mol/l of o2, calculate the equilibrium concentration of no in mol/l how would this be done?

At element makes up all organic compounds?

What is the empirical formula of a compound that is 50.7% antimony and 49.3% selenium ?