Question

A chemistry student wants to mix 50 mL of water at 25°C with 50 mL of ethanol at 25°C to make a solution. The heat of mixing for water and ethanol is -21.2 kJ/mol. Calculate the heat (in kJ) absorbed or released when the two liquids are mixed. (Assume the densities of water and ethanol are approximately 1 g/mL and 0.8 g/mL, respectively

Answer 1

First, we need to find the number of moles of water and ethanol in the solution. 1. Calculate the mass of water and ethanol:Water: Volume x Density = 50 mL x 1 g/mL = 50 gEthanol: Volume x Density = 50 mL x 0.8 g/mL = 40 g2. Calculate the number of moles for water and ethanol:Water: mass / molar mass = 50 g /  18.015 g/mol   2.776 molesEthanol: mass / molar mass = 40 g /  46.07 g/mol   0.868 moles3. Determine the limiting reactant  the one with the lowest mole ratio :Mole ratio of water to ethanol = 2.776 moles / 0.868 moles  3.2Since the mole ratio is greater than 1, ethanol is the limiting reactant. 4. Calculate the heat absorbed or released during the mixing process:Heat = moles of limiting reactant x heat of mixingHeat = 0.868 moles x  -21.2 kJ/mol   -18.4 kJThe heat released when the two liquids are mixed is approximately -18.4 kJ. Since the value is negative, it indicates that heat is released during the mixing process.