One mole of oxygen is expanded from a volume V1V_{1}V1 =1.00l=1.00 \mathrm{l}=1.00l to V2=5.01V_{2}=5.01V2=5.01 at a constant temperature T=280 K.T=280 \mathrm{~K} .T=280 K. Calculate: (a) the increment of the internal energy of the gas: (b) the amount of the absorbed heat. The gas is assumed to be a Van der Waals gas.