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25 December, 12:57

A 12.8 g sample of ethanol (C2H5OH) is burned in a calorimeter with a heat capacity of 5.65 kJ/°C. Assume the heat from the sample is negligible compared to the calorimeter. Determine the initial temperature of the calorimeter if the final temperature is 85.7°C. The molar mass of ethanol is 46.07 g/mol.

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  1. 25 December, 16:02
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    18.78° C

    Explanation:

    We are given;

    Mass of ethanol as 12.8 g Heat capacity of the calorimeter as 5.65 kJ/°C Final temperature of the calorimeter is 85.7°C Molar mass of ethanol as 46.07 g/mol

    We are required to determine the initial temperature of the calorimeter;

    Step 1: Calculate the heat released by ethanol

    First, we determine moles of ethanol

    Moles = Mass : Molar mass

    Moles = 12.8 g : 46.07 g/mol

    = 0.278 moles

    But. molar enthalpy of ethanol is 1360 kJ/mol

    Thus,

    Heat released, Q = n * ΔHc

    = 0.278 mole * 1360 kJ/mol

    =378.08 kJ

    Step 2: Calculate the heat energy absorbed by the calorimeter

    Assuming the initial temperature of the calorimeter is X

    Heat absorbed, Q = C * ΔT, Where C is the heat capacity

    Change in temperature, ΔT = (85.7 - X) °C

    Therefore;

    Q = 5.65 kJ/°C * (85.7 - X) °C

    = 484.205 - 5.65 X kilo Joules

    Step 3: Determine the initial temperature of the calorimeter We know that, the heat absorbed is equivalent to the heat released.

    Thus;

    484.205 - 5.65 X Joules = 378.08 kJ

    5.65 X = 106.125

    X = 18.78° C

    Thus, the initial temperature of the calorimeter 18.78° C
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