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Answer:
The value of W is 5.602 kJ, Q is -70.6 kJ, change in U is -65 kJ, and change in H is -70.3 kJ.
Explanation:
Based on the given information, the mass of CH3OH given is 64 grams, which is condensed isothermally and reversibly to liquid at 64 degrees C. The given standard enthalpy of vaporization of methanol at 64 degrees C is 35.3 kJ per mole.
The moles of CH3OH can be determined by using the formula,
Moles = Mass / Molar mass
= 64.0 grams / 32.0 grams per mole
= 2 mol
The amount of energy given by the process of condensation is,
ΔH = 2 mol × 35.3 kJ/mol = 70.6 kJ
In condensation heat is given off, thus, it is an exothermic process, hence, q will be -70.6 kJ
The work or W can be calculated by using the formula,
W = -P ΔV
Let us first find the volume of 2.0 mole gas at 64 °C, or 64 + 273 = 337 K,
PV = nRT
V = nRT/P
= 2 mol × 0.08206 L atm per mol K × 337 K/1 atm
= 55.3 L
As the liquid condenses in the process, the change in volume would be negligible. So, the volume change will be -55.3 L
W = - 1 atm × - 55.3 L
W = 55.3 L.atm
W = 55.3 L.atm × 101.3 J/1 L atm = 5602 J
W = 5602 × 1 kJ / 1000 J = 5.602 kJ
W = 5.602 kJ
Now U can be calculated using the formula,
U = q + W
= -70.6 kJ + 5.602 kJ
= -65. kJ
Thus, q = -70.6 kJ, W = 5.602 kJ, U = -65 kJ, and ΔH = -70.3 kJ.
The work (W) of the system is 5.602 kJ, the change in internal energy is -65 kJ, the enthalpy change is -70.3 kJ, and Q is -70.6 kJ.
What is the enthalpy change?
The heat absorbed or evolved during a reaction in a system is at constant pressure is called a change in enthalpy.
Given,
Mass of methanol = 64 gm
standard enthalpy of vaporization of methanol = 35.3 kJ per mole
Moles of methanol is calculated as:
[tex]\begin{aligned}&=\rm \dfrac{mass}{molar\;mass}\\\\&= \dfrac{64}{32}\\\\&= 2 \;\rm mol\end{aligned}[/tex]
The change in enthalpy of the system is calculated as:
[tex]\rm \Delta H = 2\;\rm mol \times 35.3 \;\rm kJ/mol = 70.6\;\rm kJ[/tex]
From the enthalpy change, it can be concluded that the system releases heat, and is an exothermic process. Therefore, q = -70.6 kJ
The work W is calculated as:
[tex]\begin{aligned}\rm W &= \rm -P \Delta V\\\\&= \rm -P (\dfrac{nRT}{P})\\\\&= \dfrac{5602 \times 1\;\rm kJ}{1000 \;\rm J}\\\\&= 5.602 \;\rm kJ\end{aligned}[/tex]
Change in internal energy is calculated as:
[tex]\begin{aligned}\rm U &= \rm q + W\\\\&= -70.6\;\rm kJ + 5.602 \;\rm kJ\\\\&= -65 \;\rm kJ\end{aligned}[/tex]
Therefore, enthalpy change = -70.3 kJ, q = -70.6 kJ, W = 5.602 kJ and internal energy change = -65 kJ.
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