For a chemical reaction $$A + B = C + D$$ ($$\Delta_r H^\ominus = 80$$ kJ mol$$^{-1}$$) the entropy change $$\Delta_r S^\ominus$$ depends on the temperature T (in K) as $$\Delta_r S^\ominus = 2T$$ (J K$$^{-1}$$ mol$$^{-1}$$). Minimum temperature at which it will become spontaneous is ______ K. (Integer)

For a reaction to become spontaneous, the Gibbs free energy change must be negative or zero: $$\Delta_r G^\circ \leq 0$$.

We know that $$\Delta_r G^\circ = \Delta_r H^\circ - T\Delta_r S^\circ$$.

Given: $$\Delta_r H^\circ = 80 \text{ kJ mol}^{-1} = 80000 \text{ J mol}^{-1}$$ and $$\Delta_r S^\circ = 2T \text{ J K}^{-1} \text{ mol}^{-1}$$.

At the minimum temperature for spontaneity, $$\Delta_r G^\circ = 0$$:

$$0 = \Delta_r H^\circ - T\Delta_r S^\circ$$

$$0 = 80000 - T(2T)$$

$$0 = 80000 - 2T^2$$

$$2T^2 = 80000$$

$$T^2 = 40000$$

$$T = \sqrt{40000} = 200 \text{ K}$$

The minimum temperature at which the reaction becomes spontaneous is $$\boxed{200}$$ K.