Question

An insulated tank initially contains 0.25 kg of a gas with an internal energy of 200 KJ/kg. Additional gas with an internal energy of 300 KJ/kg and an enthalpy of 400 KJ/kg enters the tank until the total mass of the gas contained is 1 kg. The final internal energy (in KJ/kg) of the gas in the tank is ?
a) 250
b) 275
c) 350
d) None of these

Please provide explaination to answer

Answer 1

It is not closed system and we can not use adiabatic mixing. Enthalpy of additional gas will be converted to internal energy

$$U=u_1 m_1+(1-m_1)h$$ $$U=200\cdot 0.25+(1-0.25)\cdot 400=350 (kJ)$$

specific internal energy is

$$u=350 (kJ/kg)$$