Multiple Choice
Given 313.5 g of hot tea at 72.5 °C, what mass of ice at 0 °C must be added to obtain iced tea at 12.5 °C? The specific heat of the tea is 4.18 J/(g·°C), and ΔHfusion for ice is +6.01 kJ/mol.
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8. Thermochemistry
Endothermic & Exothermic Reactions
Multiple Choice
How much energy (in kilojoules) is released when 21.5 g of ethanol vapor at 97.0 °C is cooled to -15.0 °C? Ethanol has a melting point of -114.5 °C, boiling point of 78.4 °C, ∆Hvap = 38.56 kJ/mol, and ∆Hfusion = 4.60 kJ/mol. The molar heat capacity of ethanol is 112 J/mol·K.
A
15.67 kJ
B
10.45 kJ
C
20.89 kJ
D
5.23 kJ
Verified step by step guidance1
Calculate the number of moles of ethanol using its molar mass. The molar mass of ethanol (C2H5OH) is approximately 46.08 g/mol. Use the formula: \( \text{moles} = \frac{\text{mass}}{\text{molar mass}} \).
Determine the energy released during the cooling of ethanol vapor from 97.0 °C to its boiling point at 78.4 °C using the formula: \( q = n \cdot C \cdot \Delta T \), where \( n \) is the number of moles, \( C \) is the molar heat capacity, and \( \Delta T \) is the change in temperature.
Calculate the energy released during the phase change from vapor to liquid at the boiling point using the enthalpy of vaporization: \( q = n \cdot \Delta H_{\text{vap}} \).
Determine the energy released during the cooling of liquid ethanol from 78.4 °C to its melting point at -114.5 °C using the formula: \( q = n \cdot C \cdot \Delta T \).
Calculate the energy released during the phase change from liquid to solid at the melting point using the enthalpy of fusion: \( q = n \cdot \Delta H_{\text{fusion}} \). Finally, sum all the energy changes to find the total energy released.
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