A sample of ethanol (C2H5OH) was burned completely in a bomb calorimeter whose t
ID: 511084 • Letter: A
Question
A sample of ethanol (C2H5OH) was burned completely in a bomb calorimeter whose total heat capacity is 30.75 kJ/oC. The temperature of the calorimeter plus the contents increased from 25.6oC to 35.2oC. Knowing that ethanol's heat of combustion is -3600 kJ/mol, calculate the mass of the sample (in g). Is the sign + or -? Use the following equation to "set up" this problem (be sure to multiply kJ/mole by moles to find kJ and then use the equation below): Heat Gained By Calorimeter - Heat Lost By Ethanol Heat Capacity × Tf - Ti (or T) = - Hethanol _____ kJ oC (or K) × _____ oC (or K) = _____kJ
Explanation / Answer
heat gained by calorimeter = C*(Tf-Ti)
= 30.75 KJ/oC * (35.2 - 25.6) oC
= 295.2 KJ
This is the heat lost by reaction
mol of C2H5OH = heat lost / heat of combustion
= 295.2 KJ / (3600 KJ/ mol)
= 0.082 mol
molar mass of C2H5OH = 46.0 g/mol
mass of C2H5OH = number of mol * molar mass
= 0.082 mol * 46.0 g/mol
=3.77 g
Answer: 3.77 g
Mass is always positive
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