A 12.8 g sample of ethanol (C₂H₅OH) is burned in a bomb calorimeter with a heat capacity of 5.65 kJ . Using the information below, determine the final temperature of the calorimeter if the initial temperature is 25.0°C. The molar mass of ethanol is 46.07 g . C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(g) U= -1235 kJ

Question

Quizplus · Accepted Answer

First, calculate the heat generated by the combustion of ethanol:

12.8 g ethanol x (1 mol / 46.07 g) = 0.278 mol ethanol
-1235 kJ/mol x 0.278 mol ethanol = -342.43 kJ

This heat is absorbed by the calorimeter and its contents, resulting in a temperature increase. Use the formula q = mCΔT, where q is the heat absorbed, m is the mass of the calorimeter and its contents, C is the heat capacity of the calorimeter, and ΔT is the change in temperature from the initial temperature of 25.0°C.

q = mCΔT
-342.43 kJ = (12.8 g + 1000 g) x 5.65 kJ/°C x (Tf - 25.0°C)
-342.43 kJ = 5665 J/°C x (Tf - 25.0°C)
-0.0604 kJ/°C = Tf - 25.0°C
Tf = 85.7°C

Therefore, the final temperature of the calorimeter is 85.7°C, which corresponds to choice D.

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