Calculate the specific heat of reaction of C3H8(l) at standard state for the following reaction using the data given in the table below: C3H8(l) + O2(g) → CO2(g) + 4H2O(l) | Compound | -ΔHf° [kcal/gmol] | ΔHvaporization at 25°C [kcal/gmol] | |---|---|---| | C3H8(l) | - | 3.823 | | C3H8(g) | 24.806 | - | | CO2(l) | - | 1.263 | | CO2(g) | 93.995 | - | | H2O(l) | - | 10.499 | | H2O(g) | 57.763 | - |
Answer (1)
To calculate the enthalpy change for the given reaction, we need to use Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step in the process. We will calculate the heat of reaction using the provided standard enthalpies of formation (ΔHf°) and the heats of vaporization.
Here are the steps to calculate the specific heat of reaction:
Determine the necessary reactions:
The reaction involves converting liquid propane (C₃H₈(l)) to gaseous propane (C₃H₈(g)) and gaseous carbon dioxide (CO₂(g)) to gaseous carbon dioxide (CO₂(l)), so we must consider the heats of vaporization.
Write the balanced equation: C 3 H 8 ( l ) + 5 O 2 ( g ) → 3 C O 2 ( g ) + 4 H 2 O ( l )
Find the total heat change using enthalpy of formation (ΔHf°) data:
For each component of the equation, the enthalpy change can be considered as follows:
Propane vaporization: We only have data for the vaporization from liquid to gas, which is 3.823 kcal/mol for C₃H₈(l) to C₃H₈(g).
Carbon dioxide formation: Δ H f ° ( CO 2 ( g )) = 93.995 kcal/mol
Water formation: Δ H f ° ( H 2 O ( l )) = 10.499 kcal/mol .
Calculate the reaction enthalpy (ΔHrxn°):
The enthalpy change for the reaction is obtained as a combination of the component enthalpy changes.
Since we do not have complete ΔHf° data for the liquid C₃H₈ and liquid CO₂, we can't use those towards the final calculation.
Consider the heat of reaction:
The calculation would typically require substrate-specific ΔHf° which could be looked up in standard thermodynamics tables or textbooks.
In this problem, as there are no standard heats of formation provided for C₃H₈(l), we cannot calculate the heat of reaction with the provided data alone. In a complete scenario, one would complete the table using values from a chemistry data book to fill any missing ΔHf° and complete the calculation according to standard thermodynamic practices.
