We’re being asked to identify the condition in order to decrease the yield of NH3 for the gas-phase reaction:
N2 + 3 H2 ⇌ 2 NH3 ΔH° = -92 kJ
According to Le Chatelier’s Principle, if a system (chemical reaction) is at equilibrium and we disturb it, then the system will readjust to maintain its equilibrium state.
Since the reaction is exothermic, ΔH = (–), heat is given off as a product:
N2(g) + 3 H2(g) ⇌ 2 NH3(g) + heat
Now, let’s look at the effect of changing pressure and temperature on the reaction.
For the gas phase reaction N2 + 3 H2 ⇌ 2 NH3 ΔH° = -92 kJ for the forward reaction. In order to decrease the yield of NH3, the reaction should be run
a. at high P, low T.
b. at low P, high T.
c. at high P, high T.
d. at low P, low T.
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