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Multiple Choice
What is the total change in enthalpy when 25.0 g of solid ethanol (C2H5OH) at -125 °C is converted to liquid ethanol at -80 °C? The table below provides physical and thermochemical data for ethanol. Normal melting point: -114 °C. Assume the specific heat capacities and enthalpy of fusion are known.
A
-5.0 kJ
B
12.0 kJ
C
3.5 kJ
D
7.8 kJ
Verified step by step guidance
1
Identify the processes involved in converting solid ethanol at -125 °C to liquid ethanol at -80 °C. These include heating the solid ethanol to its melting point, melting the solid ethanol, and then heating the liquid ethanol to the final temperature.
Calculate the energy required to heat the solid ethanol from -125 °C to its melting point at -114 °C using the formula: , where is the mass, is the specific heat capacity of solid ethanol, and is the change in temperature.
Calculate the energy required for the phase change from solid to liquid at the melting point using the enthalpy of fusion: , where is the enthalpy of fusion.
Calculate the energy required to heat the liquid ethanol from -114 °C to -80 °C using the formula: , where is the specific heat capacity of liquid ethanol.
Sum the energies calculated in the previous steps to find the total change in enthalpy for the conversion of solid ethanol at -125 °C to liquid ethanol at -80 °C.