Question

What mass of ethanol (C2H5OH(ℓ)) must be burned to supply 500 kJ of heat? The standard enthalpy of combustion of ethanol at 298 K is −1368 kJ · mol−1

Answer 1

Answer:

16.84 g

Explanation:

Assuming that the ethanol is free of water

the number of moles of ethanol to generate 500 KJ = 500 / 1368 = 0.3655 mol

molar mass of ethanol = 46.07 g/mol

mass of ethanol needed = 46.07 × 0.3655 = 16.84 g

Answer 2

Answer:

16.8 g

Explanation:

We are told than burning one mol of ethanol releases 1368 kJ. Now we are trying to find how much ethanol has to be burned, in grams, to release 500 kJ

We use ratios

-1368 kJ : 1 mole

-500 kJ :      x

Then you cross multiply

-1368x = -500

       x = 0.3655 mol

mass = number of moles * molar mass

        = 0.3655 mol * 46.07 g/mol

        = 16.8 g