What a learner can do afterwards
- Calculates mole fractions and partial pressures from equilibrium amounts and a total pressure
- Writes Kp for a gas reaction and works out its units
- Explains why raising the total pressure shifts the position while leaving Kp untouched
- Uses Kp to argue the conditions picked for an industrial process such as ammonia synthesis
1 · Read
Kc put a number on how far a reaction goes; for gases we write that number with pressures instead of concentrations, and it tells industry how to run its plants. In a gas mixture each gas pushes as if the others were not there. Its mole fraction is its moles over the total moles, and its partial pressure is that fraction times the total pressure.
For nitrogen plus hydrogen making ammonia, Kp is the product pressures over the reactant ones, each raised to its balancing number: p(NH3) squared over (p(N2) times p(H2) cubed), with both reactant terms in the denominator. To find the units, put pressure units into that expression and cancel them down.
Raise the total pressure and the system shifts toward the side with fewer gas moles to ease the strain. Kp itself does not move, because Kp answers only to temperature.
That is why ammonia plants run at high pressure: it pushes the yield up without touching Kp. The temperature is a compromise, hot enough for a decent rate but cool enough to protect the yield.
Share out the pressure by mole fraction, write Kp with powers, and shift position with pressure while Kp stays fixed.
2 · Watch
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.