Calculate the amount of heat energy, in units of kilojoules, required to evaporate 35.0 g of ethanol, CH₃CH₂OH, at 78.4ºC, ethanol's boiling point. (The molar heat of vaporization of liquid ethanol is 3.86 × 10⁴ J/mol. The molar mass of ethanol is 46.07 g/mol.)

Question

Quizplus · Accepted Answer

First, calculate the number of moles of ethanol: $ \frac{35.0 \, \text{g}}{46.07 \, \text{g/mol}} = 0.76 \, \text{mol} $. Then, use the molar heat of vaporization to find the heat required: $ 0.76 \, \text{mol} \times 3.86 \times 10^{4} \, \text{J/mol} = 29336 \, \text{J} = 29.3 \, \text{kJ} $.

Calculate the Amount of Heat Energy, in Units of Kilojoules