Final answer:
To find the missing equilibrium constant for the reverse reaction, calculate the reciprocal of the provided constant for the forward reaction, yielding Kc = 2.63 × 10⁻⁵.
Step-by-step explanation:
The student asks to find the missing equilibrium constant (Kc) for the reverse reaction 4 HBr(g) ⇌ 2 H₂(g) + 2 Br₂(g). The provided equilibrium constant for the forward reaction H₂(g) + Br₂(g) ⇌ 2 HBr(g) is Kc = 3.8 × 10⁴. Using the relationship that the equilibrium constant for the reverse reaction is the reciprocal of the equilibrium constant for the forward reaction, we can find the missing Kc value. Therefore, the equilibrium constant for the reverse reaction is Kc = 1/(3.8 × 10⁴) = 2.63 × 10⁻⁵.
To confirm understanding, one can use the relationship K3 = K1 × K2, where K3 is the equilibrium constant for the overall reaction that is the sum of two or more reactions, and K1 and K2 are the equilibrium constants for the individual reactions involved.