Chemistry · EQUILIBRIUM

For the dimerization reaction \( 2\text{NO}_2(\text{g}) \rightleftharpoons \text{N}_2\text{O}_4(\text{g}) \) with \( \Delta H = -57.2\text{ kJ mol}^{-1} \), what change is observed in the brown colour of the gas mixture when the temperature is lowered from \( 298\text{ K} \) to \( 270\text{ K} \) in a sealed tube?

1. The brown colour intensifies because \( \text{NO}_2 \) is favoured at lower temperatures
2. There is no colour change because equilibrium constants are temperature independent
3. The brown colour turns dark yellow due to conversion into liquid \( \text{NO} \)
4. The brown colour fades because the forward exothermic reaction is favoured, forming colourless \( \text{N}_2\text{O}_4 \)