For the reaction #"N"_2"O"_4(g) rightleftharpoons 2"NO"_2(g)#, at what temperature does #K_c# numerically equal #K_p#?
#a)# #"0.1203 K"#
#b)# #"12.19 K"#
#c)# #"273 K"#
#d)# #"298 K"#
2 Answers
I got
For ideal gases,
#n/V# is concentration in#"mol/L"# #P_("N"_2"O"_4) = (nRT)/(V) = ["N"_2"O"_4]RT# , the partial pressure of#"N"_2"O"_4# .#P_("NO"_2) = (nRT)/(V) = ["NO"_2]RT# , the partial pressure of#"NO"_2# .
Recall that stoichiometric coefficients become exponents in equilibrium expressions for gases and aqueous solutions.
So, to relate
#K_c = (["NO"_2]^2)/(["N"_2"O"_4])#
#bb(K_p) = (P_("NO"_2)^2)/(P_("N"_2"O"_4))#
#= (["NO"_2]RT)^2/(["N"_2"O"_4]RT)#
#= bb(RT(["NO"_2]^2)/(["N"_2"O"_4]) = K_cRT# , with units of pressure
Since we are wondering when numerically,
#=> RTK_c = K_p# in#"atm"#
Thus,
#=> color(blue)(T = (K_p)/(RK_c))#
It is implied that
So,
Explanation:
The relationship between
The only way that
When the question states
You need to assume that pressure is normalised against 1 atmosphere and concentration is normalised against unit concentration.
A badly worded question.