When a 10.03 g sample of ethanol, C_2H_5OH_1 is burned in a calorimeter whose he

Question

When a 10.03 g sample of ethanol, C_2H_5OH_1 is burned in a calorimeter whose heat capacity is 42.2 kJ/degree C, the calorimeter heated up from 15.0 degree C to 43.1 degree C. Use this information to determine the molar heat of combustion of ethanol. Bonus: If the accepted molar enthalpy of combustion of ethanol is -6453.4 kJ/mol, what is the percent error for this experiment? The incomplete combustion of pentane is shown in the balanced equation below. Given H_inc =-1829.8 kJ/mol, add the correct energy term to the appropriate side of the equation. Use a potential energy diagram to show this reaction

Explanation / Answer

First, let's calculate the heat:

Q = Cp(Tf-Ti)
Q = 42.2 (15-43.1)
Q = -1185.82 kJ

To calculate the enthalpy, we need the moles:
moles ethanol = 10.03 g / (46 g/mol) = 0.218 moles

dH = Q/n = 1185.82 / 0.218 = -5439.54 kJ/mol

The % error would be:
% = 6453.4 - 5439.54/6453.4 * 100 = 15.71%

The second question post it in another question thread. Hope this helps

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