I only need help with b. can you please type out the answer. Please show all the
ID: 716472 • Letter: I
Question
I only need help with b. can you please type out the answer. Please show all the work necessary for b.
The enthalpy of combustion of benzoic acid (C6H5COOH) is commonly used as the standard for calibrating constant-volume bomb calorimeters; its value has been accurately determined to be – 3226.7 kJ/mol.
(a) When 0.9862 g of benzoic acid was oxidized, the temperature rose from 21.84 °C to 25.67 °C. What was the heat capacity of the calorimeter?
(b) In a separate experiment, 0.4654 g of a-D-glucose (C6H12O6) was oxidized in the same calorimeter, and the temperature rose from 21.22 °C to 22.28 °C. Calculate the enthalpy of combustion of glucose and the value of DUrxn for the combustion. (Hint: Be sure to write a balanced equation for each reaction first and assume the product H2O is a liquid)
Explanation / Answer
a)
Enthalpy dH = - 3226.7 kJ/mol
mass of benzoic acid = 0.9862 g
moles of benzoic acid = 0.9862 / 122.12 = 8.076 x 10^-3 mol
temperature rise = 25.67 - 21.84 = 3.83 oC
Q = n x dH = 8.076 x 10^-3 x 3226.7
= 26.06 kJ
Q = Cp dT
26.06 = Cp x 3.83
Cp = 6.804 kJ / oC
heat capacity of calorimeter = 6.804 kJ/ oC
b)
moles of D- glucose = 0.4654 / 180 = 2.586 x 10^-3 mol
dT = 22.28 - 21.22 = 1.06
Q = Cp dT
= 6.804 x 1.06
Q = 7.212
delta H combustion = 7.212 / 2.586 x 10^-3
dHcomb = - 2789 kJ/mol
DUrxn = - 2789 kJ/mol