Comparing water's 4.18 kJ/kg-K * ~75 K (25 °C -> 100 °C) to the sand's 1.1 kJ/kg-K * 900 K? I think you can (or it's easier) get more useful work out of a less

Comparing water's 4.18 kJ/kg-K * ~75 K (25 °C -> 100 °C) to the sand's 1.1 kJ/kg-K * 900 K? I think you can (or it's easier) get more useful work out of a lesser amount of hotter stuff, even if the thermal energy or total heat is the same. Unsure of that, I don't know what the specific principle is. I'd vaguely gesture at the 2nd law of thermo as if I poured a cup of boiling water into a pot of room-temperature water, the total heat leaving the pot would wind up being the same as the heat leaving the cup, but less useful?