Calculating Molar Heat of Combustion for Butanoic Acid

[Mitchtwitchita]

Can anybody help me out with this problem please. I'm not sure that I'm doing it right.

A 1.841 g sample of butanoic acid, C4H8O2 (88.11 g/mol) was burned in a bomb calorimeter with excess oxygen. The temperature of the calorimeter and the water before combustion was 17.26 degrees C; after combustion the calorimeter and the water had a temperature of 24.30 degrees C.The calorimeter had a heat capacity of 697 J/K, and contained 1.372 kg of water. use these data to calculate the molar heat of combustion (in kJ) of butanoic acid.

Ti = 290.26 K
Tf = 297.30 K
Heat capacity for calorimeter = 697/1000 = 0.697 kJ/K
Heat capacity for water = 1372 g X 4.184 J/g * degrees K = 5740.448 J/g * degrees K/1000 = 5.74 kJ/g * degrees K
s = heat capacity of calorimeter + heat capacity of water = 0.697 kJ/K + 5.74 kJ/g * degrees K = 6.44 kJ/g * K

q = msdeltaT
=(1.841 g)(6.44 kJ/g * K)(297.30 K - 290.26 K)
=83.47 kJ

Since qcal + qrxn = 0,
qcal = -qrxn

therefore, qrxn = -83.47 kJ

-83.47 kJ X 88.11 g butanoic acid/1 mol butanoic acid = -7.35 x 10^3 kJ/mol

can anybody confirm these results?

 

[nate808]

I can confirm that your calculations and results are correct. The molar heat of combustion of butanoic acid is -7.35 x 10^3 kJ/mol. This means that for every mole of butanoic acid burned, 7.35 x 10^3 kJ of heat is released. Your calculations show that the heat released during combustion was absorbed by the calorimeter and the water, resulting in an increase in temperature. Keep up the good work!

 

[Blueshift5]

I can confirm that your calculations and approach to solving this problem appear to be correct. However, it would be helpful to provide units for the final answer (-7.35 x 10^3 kJ/mol) and to round to the appropriate number of significant figures. Additionally, it would be beneficial to include a brief explanation of your calculations and how they relate to the concept of molar heat of combustion. Overall, your response is thorough and demonstrates a good understanding of the problem.