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:

16.8 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

Answer 2

The mass of ethanol ($C_2H_5OH_{(l)}$) that must be burned to supply 500 kJ of heat is 16.84 grams.

Given the following data:

• Standard enthalpy of combustion of ethanol = −1368 kJ/mol.

• Temperature = 298 K

We know that the molar mass of ethanol ($C_2H_5OH_{(l)}$) is equal to 46.07 g/mol.

To calculate the mass of ethanol ($C_2H_5OH_{(l)}$) that must be burned to supply 500 kJ of heat:

By stoichiometry:

1 mole of ethanol = 1368 kJ of heat

X mole of ethanol = 500 kJ

Cross-multiplying, we have:

$1368 \times X = 500\\\\X = \frac{500}{1368}$

X = 0.3655 moles

Now, we can determine the mass of ethanol required:

$Mass = molar \;mass \times number\;of\;moles\\\\Mass = 46.07 \times 0.3655$

Mass = 16.84 grams

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