Problem:
What is the heat capacity of the newly assembled oxygen bomb calorimeter?
Experimental design:
An oxygen calorimeter is assembled and several samples of the primary standard, benzoic acid are burned using a constant pressure of excess oxygen. The evidence that is collected determines the heat capacity of the calorimeter for the future experiments.
Evidence:
In the CRC Handbook of chemistry and physics, the molar enthalpy of combustion for benzoic acid is reported as
Hc= -3231 kJ/ mol
C6H5COOH
Calorimetric Evidence for the burning of Benzoic Acid
Mass of C6H5COOH (s) (g)
Trial 1: 1.024
Trial 2:1.043
Trial 3:1.035
Initial temperature (°C)
hard
To determine the heat capacity of the newly assembled oxygen bomb calorimeter, you can use the heat transfer equation:
q = C * ΔT
Where:
- q is the heat transferred to the calorimeter
- C is the heat capacity of the calorimeter
- ΔT is the change in temperature of the calorimeter
In this case, you need to determine the heat transferred to the calorimeter from the combustion of benzoic acid. The molar enthalpy of combustion for benzoic acid is given as -3231 kJ/mol.
To calculate the heat transferred to the calorimeter, you can use the following steps:
1. Calculate the moles of benzoic acid burned in each trial using the mass of benzoic acid and its molar mass (122.12 g/mol).
Trial 1:
moles = mass / molar mass = 1.024 g / 122.12 g/mol
= 0.0084 mol
Trial 2:
moles = mass / molar mass = 1.043 g / 122.12 g/mol
= 0.0085 mol
Trial 3:
moles = mass / molar mass = 1.035 g / 122.12 g/mol
= 0.0085 mol
2. Calculate the heat transferred to the calorimeter in each trial using the molar enthalpy of combustion.
Trial 1:
q = moles * Hc
= 0.0084 mol * -3231 kJ/mol
= -27.11 kJ
Trial 2:
q = moles * Hc
= 0.0085 mol * -3231 kJ/mol
= -27.45 kJ
Trial 3:
q = moles * Hc
= 0.0085 mol * -3231 kJ/mol
= -27.45 kJ
3. Calculate the change in temperature of the calorimeter using the initial temperature.
ΔT = final temperature - initial temperature
4. Average the heat transferred and the change in temperature over the trials.
5. Finally, using the average heat transferred (q) and the average change in temperature (ΔT), solve the heat transfer equation for the heat capacity of the calorimeter (C).
C = q / ΔT
Please note that the units of heat capacity will depend on the units used for q and ΔT.