Question

Consider the following equilibrium:

4Fe(s) + 3 O2(g) <-- --> 2Fe2O3(s);

Which of the following equations is wrong?

Kp=Kc(RT)-5

Kp= Kc(RT)-3

Kp = PO2-3

Kc=[O2]-3

Answer 1

l think the answer is kc=:02:-3

Answer 2

Answer : The wrong equation is,
`K_p=K_c* (RT)^(-5)`

Explanation :

The given equilibrium reaction is,

`4Fe(s)+3O_2(g)\rightarrow 2Fe_2O_3(s)`

The expression for equilibrium constant in terms of concentration,

`K_c=(1)/([O_2]^3)\\\\K_c=[O_2]^(-3)`

The expression for equilibrium constant in terms of pressure,

`K_p=(1)/((P_(O_2))^3)\\\\K_p=(P_(O_2))^(-3)`

The relation between the equilibrium constant in terms of concentration and equilibrium constant in terms of pressure will be,

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

where,

`\Delta n_g`= number of moles of gaseous products - number of moles of gaseous reactants

R = gas constant

T= temperature

For reaction the given reaction,

`\Delta n_g`= number of moles of gaseous products - number of moles of gaseous reactants= 0 - 3 = -3

`K_p=K_c* (RT)^(-3)`

Therefore, the correct equations for equilibrium are,
`K_c=[O_2]^(-3)`,
`K_p=(P_(O_2))^(-3)` and
`K_p=K_c* (RT)^(-3)`