Question

In which of the following reactions will Kc = Kp? a. 4 NH3(g) + 3 O2(g) ⇌ 2 N2(g) + 6 H2O(g) b. SO3(g) + NO(g) ⇌ SO2(g) + NO2(g) c. 2 N2(g) + O2(g) ⇌ 2 N2O(g) d. 2 SO2(g) + O2(g) ⇌ 2 SO3(g)

Answer 1

Answer:

The correct option is b) SO₃(g) + NO(g) ⇌ SO₂(g) + NO₂(g)

Explanation:

The relation between Kc and Kp is given by the following equation:

$Kp = Kc (RT)^{dn}$

where R is the gas constant (0,082 L.atm/K.mol), T is the temperature (in K) and dn is the change in moles.

The change in moles (dn) is calculated as:

dn = moles of products - moles reactants

If dn=0, RT= 1 ⇒ Kc=Kp

We calculate dn for each reaction from the estequiometrial coefficients of products and reactants as follows:

a) 4 NH₃(g) + 3 O₂(g) ⇌ 2 N₂(g) + 6 H₂O(g)

dn= (2+6) - (4+3) = 1 ⇒ Kc ≠ Kp

b) SO₃(g) + NO(g) ⇌ SO₂(g) + NO₂(g)

dn = (1+1) - (1+1)= 0 ⇒ Kc = Kp

c) 2 N₂(g) + O₂(g) ⇌ 2 N₂O(g)

dn= 2 - (2+1) = -1 ⇒ Kc ≠ Kp

d) 2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g)

dn = 2 - (2+1) = -1 ⇒ Kc ≠ Kp

The reaction in which Kc=Kp is b), because reactants and products have the same number of moles.