A12.8 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.

18.78° C

We are given;

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

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

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

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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