Acetone \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\), is a common organic solvent with relatively low melting point \((178 \mathrm{~K})\) and boiling point $(329 \mathrm{~K})\(. The enthalpy of fusion of acetone is \)5.72 \mathrm{~kJ} / \mathrm{mol}\(, and its enthalpy of vaporization is \)29.1 \mathrm{~kJ} / \mathrm{mol}\(. The specific heats of solid and liquid acetone are \)96 \mathrm{~J} / \mathrm{mol}-\mathrm{K}\( and \)125.5 \mathrm{~J} / \mathrm{mol}-\mathrm{K}$ respectively. (a) How much heat is required to convert \(23.0 \mathrm{~g}\) of acetone at \(273 \mathrm{~K}\) to the vapor phase at \(329 \mathrm{~K} ?(\mathbf{b})\) How much heat is required to convert the same amount of acetone at \(77 \mathrm{~K}\) to the vapor phase at $329 \mathrm{~K} ?$

Short Answer

Expert verified
(a) The total heat required to convert 23.0 g of acetone at 273 K to the vapor phase at 329 K can be found by calculating and adding the heat required to heat the solid and liquid acetone, melting, and vaporization: \(q_{total} = q_{solid} + q_{fus} + q_{liquid} + q_{vap} = 0.396 \text{ mol} * 96 \frac{\text{J}}{\text{mol} \cdot \text{K}} * (178 \text{ K} - 273 \text{ K}) + 0.396 \text{ mol} * 5.72 \frac{\text{kJ}}{\text{mol}} + 0.396 \text{ mol} * 125.5 \frac{\text{J}}{\text{mol} \cdot \text{K}} * (329 \text{ K} - 178 \text{ K}) + 0.396 \text{ mol} * 29.1 \frac{\text{kJ}}{\text{mol}}\) (b) To find the heat required to convert the same amount of acetone at 77 K to the vapor phase at 329 K, calculate the heat required to heat the solid acetone from 77 K to the melting point, then follow steps 3-6 from part (a), and finally add all heat values: \(q_{total} = q_{solid} + q_{fus} + q_{liquid} + q_{vap} = 0.396 \text{ mol} * 96 \frac{\text{J}}{\text{mol} \cdot \text{K}} * (178 \text{ K} - 77 \text{ K}) + q_{fus} + q_{liquid} + q_{vap}\)

Step by step solution

01

Calculate the number of moles of acetone

First, calculate the number of moles (n) of acetone using its molar mass, 58.08 g/mol: n = (mass) / (molar mass) n = (23.0 g) / (58.08 g/mol) n = 0.396 mol
02

Calculate the heat required to heat acetone from 273 K to its melting point, 178 K

We'll use the specific heat of solid acetone (C_s = 96 J/mol-K) and the temperature difference to calculate the heat needed (q_solid): q_solid = n * C_s * (T₂ - T₁) q_solid = 0.396 mol * 96 J/mol-K * (178 K - 273 K)
03

Calculate the heat required for melting acetone

Use the enthalpy of fusion (ΔH_fus = 5.72 kJ/mol) to calculate the heat needed (q_fus): q_fus = n * ΔH_fus q_fus = 0.396 mol * 5.72 kJ/mol
04

Calculate the heat required to heat liquid acetone from its melting point to its boiling point

We'll use the specific heat of liquid acetone (C_l = 125.5 J/mol-K) and the temperature difference to calculate the heat needed (q_liquid): q_liquid = n * C_l * (T₄ - T₃) q_liquid = 0.396 mol * 125.5 J/mol-K * (329 K - 178 K)
05

Calculate the heat required for vaporization of acetone

Use the enthalpy of vaporization (ΔH_vap = 29.1 kJ/mol) to calculate the heat needed (q_vap): q_vap = n * ΔH_vap q_vap = 0.396 mol * 29.1 kJ/mol
06

Calculate the total heat required

Add the heat required for heating solid and liquid acetone, melting, and vaporization: q_total = q_solid + q_fus + q_liquid + q_vap (b) Heat required to convert the same amount of acetone at 77 K to the vapor phase at 329 K
07

Calculate the heat required to heat acetone from 77 K to its melting point, 178 K

We'll use the specific heat of solid acetone (C_s = 96 J/mol-K) and the temperature difference to calculate the heat needed (q_solid): q_solid = n * C_s * (T₂ - T₁) q_solid = 0.396 mol * 96 J/mol-K * (178 K - 77 K) Follow steps 3-6 from part (a) to calculate the corresponding heat values.
08

Calculate the total heat required

Add the heat required for heating solid and liquid acetone, melting, and vaporization: q_total = q_solid + q_fus + q_liquid + q_vap

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