Answer
$m_2=12,697\ kg$
$Q=-899,545.28\ kJ$
Work Step by Step
$m_a=PV/RT$
Constant $P=1500\ kPa, T=288.15\ K,\ R=0.287\ kJ/kg.K$
Initial $V_1=100\ m³$: $m_1=1814\ kg$
Final $V_2=700\ m³$: $m_2=12,697\ kg$
Water: $m_w=V_1/v,\ V_1=600\ m³$: $m_w=600,000\ kg$
Energy balance:
$Q+m_ih_i-m_eh_e=m_2u_2-m_1u_1$
$Q=m_2c_vT-(m_1c_vT+m_wu_w)+m_wh_w-(m_2-m_1)c_pT$
$u_w\approx h_w$
$Q=(m_2-m_1)c_vT-(m_2-m_1)c_pT,\ c_v=0.718,\ c_p=1.005\ kJ/kg.K$
$Q=-899,545.28\ kJ$
