If it's in equilibrium, what change will cause more NH3 to form in this equation: N2(g) + 3H2(g) 2NH3(g)?

Question

By the way, the enthalpy of the reaction is: ΔH = -92.5 kJ/mol

So, will increasing the volume of the system cause more NH3 to form? Will decreasing the pressure cause more NH3 to form? What about lowering the temperature? Or, lowering the enthalpy of the reaction?

Answer 1

You're taking two compounds and combining them into one compound.

If you decrease the pressure (which is the same as increasing the volume), you won't be "squishing" the two reactants into one anymore, so the amount of NH3 will decrease.

Likewise, lowering the temperature has the effect of lowering the pressure. Same result as above: Less NH3 produced.

Lowering the enthalpy: Gibbs Free Energy applies here, so deltaG=deltaH-TdeltaS.

TdeltaS is going to be negative, as we're going from two molecules (more random) to one. In effect, we're increasing the order/decreasing the randomness of the system.

If TdeltaS is negative, subtracting it makes it a positive.

If we decrease the enthalpy, the Gibbs Free Energy has to thus decrease overall.

The smaller Gibbs Free energy, the more "spontaneous" a reaction. You'd increase the amount of NH3 produced.

Answer 2

In this reaction, four molecules become two molecules. So increasing the volume or decreasing the pressure will lead to fewer molecules of NH3. One cannot change the enthalpy ofthe reaction (First Law of Thermodynamics).