The following information is given for ethanol, C2H5OH, at 1atm:

boiling point = 78.4oC Hvap(78.4oC) = 38.6 kJ/mol
melting point = -115oC Hfus(-115oC) = 5.02 kJ/mol
specific heat liquid = 2.46 J/goC

At a pressure of 1 atm, what is H in kJ for the process of condensing a 40.8 g sample of gaseous ethanol at its normal boiling point of 78.4 oC

to a liquid at -115 oC?

H = (38.6 kJ/mol + 5.02 kJ/mol) x (40.8 g/46.07 g/mol) = 8.45 kJ

To solve this problem, we need to calculate the amount of energy required to condense the gaseous ethanol at its normal boiling point.

Step 1: Calculate the number of moles of ethanol in the 40.8 g sample.
Given mass = 40.8 g
Molar mass of ethanol (C2H5OH) = (2 * 12.01 g/mol) + (6 * 1.01 g/mol) + 16.00 g/mol = 46.07 g/mol

Number of moles = mass / molar mass
Number of moles = 40.8 g / 46.07 g/mol

Step 2: Calculate the heat released during condensation using the enthalpy of vaporization (Hvap) at the boiling point.
Hvap(78.4oC) = 38.6 kJ/mol
Heat released = Hvap * number of moles

Step 3: Convert the heat released from Joules to kilojoules.
1 kJ = 1000 J
Heat released (kJ) = Heat released (J) / 1000

Now, let's perform the calculations:

Number of moles = 40.8 g / 46.07 g/mol ≈ 0.886 mol

Heat released = 38.6 kJ/mol * 0.886 mol ≈ 34.162 kJ

Therefore, the heat released during the condensation of a 40.8 g sample of gaseous ethanol at its normal boiling point of 78.4 oC is approximately 34.162 kJ.

To find the enthalpy change (H) for the process of condensing the gaseous ethanol, you need to calculate the heat transfer involved in transitioning the substance from a gas to a liquid.

The formula to calculate the heat transfer in a phase change is:

Q = m * ΔH

Where:
Q is the heat transfer
m is the mass of the substance
ΔH is the enthalpy change (heat of transformation)

Here's how you can solve the problem step-by-step:

1. Convert the given mass of the sample from grams to moles. To do this, divide the mass by the molar mass of ethanol (C2H5OH), which is approximately 46.07 g/mol.
40.8 g ÷ 46.07 g/mol = 0.885 mol

2. Calculate the heat transfer involved in the phase change from gas to liquid. Since the substance is undergoing condensation, the enthalpy change is given by Hvap(78.4 °C), which is 38.6 kJ/mol.
Q = m * ΔH
Q = 0.885 mol * 38.6 kJ/mol = 34.129 kJ

Therefore, the enthalpy change (H) for the process of condensing a 40.8 g sample of gaseous ethanol at its normal boiling point of 78.4 °C is 34.129 kJ.