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

Question

Quizplus · Accepted Answer

First, we need to calculate the moles of ethanol required to release 500 kJ of heat:

∆H = q = 500 kJ
n = ∆H / ∆H° = 500 kJ / (-1368 kJ/mol) = -0.365 mol

Note that the negative sign indicates that the reaction is exothermic, releasing heat.

Since the molar mass of ethanol is approximately 46 g/mol, we can calculate the mass required:

mass = n x molar mass = (-0.365 mol) x (46 g/mol) = -16.8 g

The negative sign here is invalid since mass cannot be negative, so we take the absolute value:

mass = 16.8 g

Therefore, the best choice is C.

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