How much energy does it take to boil 100ml of water apex

100 mL × × × 40.65 kJ/mol = 226 kJ

Explanation:

It depends a little on what temperature it is to start with.  

The heat capacity of water is 4.184 J g–1 K–1 (which in calories is equal to 1 cal g–1 K–1), which means that it takes a little more than 4 Joules to heat 1 gram of water 1 °C.   That means if the water is at room temperature (25 °C) you have to raise the temperature by 75 °C to reach the boiling point.  

So 1 lb of water is is 453.59 grams, so that gives 1898.5 Joules (1.898 kJ) or 7943.3 calories (7.943 kcal) to heat 1 pound of water 75°C.  

But that's just to get it to the boiling point.  You then need more energy to convert the liquid water at 100 °C into gaseous water at 100 °C, and for that you need something called the heat of vaporization.  For water that is 2258 J g-1(or 539.7 cal g-1).  

So, multiplying by 453.59 g/lb, we get 1,024,357 J lb-1 (or 1024 kJ/lb), or 244.83 kcal per lb.  

So most of the energy goes into turning water at 100 °C into steam at 100 °C, and so the answer is approximately 1025 kJ per pound, or 250 kcal per pound.