Before the system was compressed, the partial pressure of NH3 was only about 1% of the total pressure. After the system is compressed, the partial pressure of NH3 is almost 10% of the total.
These data provide another example of Le Chatelier's principle. A reaction at equilibrium was subjected to a stress an increase in the total pressure on the system. The reaction then shifted in the direction that minimized the effect of this stress. The reaction shifted toward the products because this reduces the number of particles in the gas, thereby decreasing the total pressure on the system, as shown in the figure below.