Question

If the reaction below has a Kp =1.9 × 106 at 400°C, what is Kc?

N2O(g) + NO2(g) 3NO(g)

A.
2.9 × 104
B.
5.3 × 106
C.
0.016
D.
0.16

Answer 1

Answer : The value of
`K_c` is
`3.4* 10^(4)`

Explanation :

The balanced equilibrium reaction is,

`N_2O(g)+NO_2(g)\rightleftharpoons 3NO(g)`

The relation between
`K_p` and
`K_c` are :

`K_p=K_c* (RT)^(\Delta n)`

where,

`K_p` = equilibrium constant at constant pressure =
`1.9* 10^6`

`K_c` = equilibrium concentration constant = ?

R = gas constant = 0.0821 L⋅atm/(K⋅mol)

T = temperature =
`400^oC=273+400=673K`

`\Delta n` = change in the number of moles of gas = [(3) - (1 + 1)] = 1 (from the chemical reaction)

Now put all the given values in the above relation, we get:

`(1.9* 10^6)=K_c* (0.0821L.atm/K.mol* 673K)^(1)`

`K_c=3.4* 10^(4)`

Thus, the value of
`K_c` is
`3.4* 10^(4)`

Answer 2

A. 2.9 x 10^4

NOTE: When I did the calculations, I got the same amount as the person above so the answers in this question might be wrong.

Step-by-step explanation:

Kp = 1.9 x 10^6, written in standard form: 1,900,000. Since the pressure is high (k < 1), the reaction favors the products so C. and D. are wrong.

Now it is either A. or B.

Kp, which is 1,900,000, is the total calculated pressure of the partial pressures of the reaction. That means B. 5.3 x 10^6, written out as 5,300,000 cannot be the Kc because it exceeds Kp = 1,900,000.

Also, Kp and Kc (partial pressure and concentration), are proportional to each other.

Therefore the answer is A. 2.9 x 10^4.