How do you test for the presence of ammonia gas?

The Haber's process describes the industrial production of ammonia gas on a large scale: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{ }{\rightleftharpoons }2{\mathrm{NH}}_3\left(\mathrm{g}\right); ∆{\mathrm{H}}^{°}=-92 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Predict the effect of the following change on the position of the equilibrium in the process.

Nitrogen gas is added to the system at equilibrium. 

The Haber's process describes the industrial production of ammonia gas on a large scale: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{ }{\rightleftharpoons }2{\mathrm{NH}}_3\left(\mathrm{g}\right); ∆{\mathrm{H}}^{°}=-92 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Predict the effect of the following change on the position of the equilibrium in the process.

Hydrogen gas is removed from the system at equilibrium. 

The Haber's process describes the industrial production of ammonia gas on a large scale: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{ }{\rightleftharpoons }2{\mathrm{NH}}_3\left(\mathrm{g}\right); ∆{\mathrm{H}}^{°}=-92 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Predict the effect of the following change on the position of the equilibrium in the process.

The pressure of the system is decreased.

The Haber's process describes the industrial production of ammonia gas on a large scale: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{ }{\rightleftharpoons }2{\mathrm{NH}}_3\left(\mathrm{g}\right); ∆{\mathrm{H}}^{°}=-92 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Predict the effect of the following change on the position of the equilibrium in the process.

The temperature of the system is increased.

The decomposition of sulphur trioxide is an endothermic process: $2{\mathrm{SO}}_3\left(\mathrm{g}\right)\stackrel{ }{\rightleftharpoons }2{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right); ∆\mathrm{H}=+196 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Predict the effect of the following change on the position of the equilibrium:

Sulphur trioxide gas is removed from the system at equilibrium.