A sealed chamber containing 32.5 g of molecular oxygen and 20.2 g of molecular nitrogen at 48.0 °C is cooled down to 20.2 °C. Given that for N₂, c_υ = 0.743 kJ/kg · K, and for O₂, c_υ = 0.659 kJ/kg · K, determine the resulting change in the internal energy of the gas.