The unit of energy, 1 dm³ atm, is equal to how many calories?
$1\ \mathrm{dm^3} = 1\times 10^{-3}\ \mathrm{m}^3 $ 

$1\ \mathrm{atm = 1013.25\ mbar = 101.325 kPa = 101325\ {kg}\cdot{}m^{-1}\cdot s^{-2}}$

$1\ \mathrm{atm \cdot dm^3} = 1\times 10^{-3}\cdot 101325\ \mathrm{m^3 \cdot kg \cdot{}m^{-1}\cdot s^{-2}} = 101.325\ \mathrm{kg \cdot{}m^{2}\cdot s^{-2}}$

$ 1\ \mathrm{atm \cdot dm^3 = 101.325\ J = 101.325\cdot 0.2390\ cal= 24.217\ cal}$