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Sagot :
m=2.65kg=2650g
M=74g/mol
n = m/M = 2650g/74g/mol ≈ 35.81mol
Heat of fusion = 7.27kJ/mol
If 7.27kJ ------------- energy is in --------------- 1mol
than x ------------- energy is in --------------- 35.81mol
x = [35.81mol*7.27kJ]/1mol = 260.3387kJ
M=74g/mol
n = m/M = 2650g/74g/mol ≈ 35.81mol
Heat of fusion = 7.27kJ/mol
If 7.27kJ ------------- energy is in --------------- 1mol
than x ------------- energy is in --------------- 35.81mol
x = [35.81mol*7.27kJ]/1mol = 260.3387kJ
The amount of energy released when [tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex] freezes is [tex]\boxed{{\text{259}}{\text{.92 kJ}}}[/tex].
Further explanation:
Heat of fusion measures the amount of energy needed to heat given mass of a solid to change its state into liquid. Also, it represents the amount of energy given up when a given mass of liquid solidifies.
When a substance converts from its phase from solid to liquid, the change in enthalpy [tex]\left({\Delta H}}}\right)[/tex] is positive, and if the substance transforms from liquid state to solid state then the change in enthalpy[tex]\left({\Delta H}}}\right)[/tex] is negative.
The expression to relate the energy released and heat of solidification is as follows:
[tex]{\text{Energy released}}={\text{n}}\times\left({{\Delta }}{{\text{H}}_{{\text{solidification}}}}}\right)[/tex]
Given mass of [tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex] is 2.65 kg.
The conversion factor to convert mass in (g) from (kg) is written as follows:
[tex]{\text{1kg}}=1000\;{\text{g}}[/tex]
So, 2.65 kg of mass is converted into (g) as follows:
[tex]\begin{aligned}{\text{Mass}}&=\,\left({2.65\;{\text{kg}}} \right)\left( {\frac{{{\text{1000}}\;{\text{g}}}}{{{\text{1}}\;{\text{k}}{\text{g}}}}}\right)\\&={\text{2650 g}}\\\end{aligned}[/tex]
Molar mass of [tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex] is 74.12 g/mol.
The moles of [tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex]can be calculated as follows:
[tex]\begin{aligned}{\text{number of moles }}&=\frac{{{\text{mass of (}}{{\text{C}}_2}{{\text{H}}_5}{{\text{)}}_2}{\text{O}}}}{{{\text{molar mass of (}}{{\text{C}}_2}{{\text{H}}_5}{{\text{)}}_2}{\text{O}}}}\\&=\frac{{{\text{2650 g}}}}{{{\text{74}}{\text{.12}}\;{\text{g/mol}}}}\\&=35.752{\text{ mol}}\\\end{aligned}[/tex]
The heat of fusion for diethyl ether[tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex]is 7.27 kJ/mol and therefore the heat of solidification for diethyl ether[tex]{{\text{(}}{{\text{C}}_2}{{\text{H}}_5}{\text{)}}_2}{\text{O}}[/tex]is -7.27 kJ/mol.
The formula to calculate the amount of energy released is as follows:
[tex]{\text{Amount of energy}}={\text{number of moles}}\times{\Delta }}{{\text{H}}_{{\text{solidification}}}}{\text{ }}[/tex] …… (1)
Substitute 35.752 mol for number of moles and -7.27 kJ/mol for [tex]{\Delta }}{{\text{H}}_{{\text{solidification}}}}[/tex] in the equation (1).
[tex]\begin{aligned}{\text{Amount of energy}}&=\left({35.752\;{\text{mol}}}\right)\left({-7.27{\text{kJ/mol}}}\right)\\&=-259.92{\text{ kJ}}\\\end{aligned}[/tex]
Therefore, the amount of energy released is [tex]{\mathbf{259}}{\mathbf{.92 kJ}}[/tex].
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Answer details:
Grade: Senior School
Subject: Chemistry
Chapter: Thermodynamics
Keywords: Heat of fusion, number of moles, enthalpy, enthalpy change, released, absorbed, 259.91 kJ, 7.27kJ/mol, and 35.752 mol.
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