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I know how to do this problem. We must find the value of K to compare to the value of Q, which can easily be calculated.

I know that the equation we use to get a K out of delta G is as follows:

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However, does this equation give us a Kp or a Kc value? What would it give me in this problem if I plugged in the provided delta G standard value?

I calculated the value of this K (whatever it is) to be 1.00, and I also calculated the Qc and Qp for this problem to be 0.00005 and 0.36, respectively. So clearly, Qc and Qp are both less than K. But how can we determine of Qc is really < Kc in this problem?

Dissenter
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  • Just out of learning curiosity, the system isn't at equilibrium at 25'C? and reaction begins with both reactants and products present? Can we say for any reaction Qc < Kc initially and Qc increases as more products are created towards equilibrium? – bonCodigo Jul 24 '17 at 23:17

1 Answers1

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The equation yields Kp.

$$\Delta G^{o}=-RTln(K_p)$$

There is, however, a relationship betweek Kp and Kc.

$$K_p = K_c(RT)^{\Delta n} $$

From the balanced equation there are 3 moles of gas on the right (2+1) and 1 mole of gas on the left. In chem, delta means final minus initial and we arrive at $$\Delta n = 3-1=2$$

and you now can find Kc. Note that you should use 0.08206 L•atm/mol•K for R.

Sources:

  1. Zumdhal example 13.5

  2. https://www.quora.com/In-a-gas-equilibrium-which-K-constant-is-used-in-the-equation-%CE%94G-RTlnK-Kp-or-Kc

PhysicalChemist
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