Q=cm△t=4.2*10^3kg/°C*2kg*(100-20)=6.72*10^5JQ=qV=3.0*10^7J/kg*V酒精=6.72*10^5JV酒精=0.0224m^3m酒精=ρ酒精*V酒精=0.8*10^3kg/m^3*0.0224m^3=17.92kg