Derive the integrated rate expression for a first order reaction.

For the reaction, ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)⟶2{\mathrm{NH}}_3\left(\mathrm{g}\right),$ how is the rate of formation of ammonia related to the rate of disappearance of hydrogen? How is the order of this reaction influenced when nitrogen is present in excess?