Enthalpy of Combustion

The enthalpy of combustion is the amount of heat released or absorbed when a substance undergoes complete combustion with oxygen. It is a measure of the energy content of a substance.

Oxalic Acid

Oxalic acid is a compound with the formula H2C2O4. It is a crystalline solid that is highly soluble in water. Oxalic acid contains two carboxyl groups (-COOH), which are responsible for its acidic properties.

Hydrated Oxalic Acid

Hydrated oxalic acid is oxalic acid that contains water molecules within its crystal structure. The water molecules are loosely bound to the oxalic acid molecules and can be released upon heating.

Combustion of Hydrated Oxalic Acid

When hydrated oxalic acid undergoes combustion, it reacts with oxygen to produce carbon dioxide (CO2), water (H2O), and heat. The balanced equation for the combustion of hydrated oxalic acid is:

H2C2O4 + O2 → 2CO2 + H2O + heat

The heat released during combustion is 2.2 kcal. This means that for every gram of hydrated oxalic acid combusted, 2.2 kcal of heat is released.

Enthalpy of Combustion Calculation

The enthalpy of combustion is defined as the heat released per mole of the substance combusted. In this case, the enthalpy of combustion of hydrated oxalic acid is given as -277.2 kcal/mol.

To calculate the enthalpy of combustion, we need to convert the heat released per gram of hydrated oxalic acid to the heat released per mole of hydrated oxalic acid.

The molar mass of hydrated oxalic acid is 126.07 g/mol. Therefore, 1 gram of hydrated oxalic acid is equal to 1/126.07 moles.

To convert the heat released per gram to the heat released per mole, we multiply the heat released per gram by the molar mass:

2.2 kcal/g × 126.07 g/mol = 277.47 kcal/mol

The calculated enthalpy of combustion, 277.47 kcal/mol, is very close to the given value of -277.2 kcal/mol, considering the rounding of significant figures.

Conclusion

The enthalpy of combustion of hydrated oxalic acid is -277.2 kcal/mol. This value represents the heat released per mole of hydrated oxalic acid combusted. The enthalpy of combustion is calculated by converting the heat released per gram to the heat released per mole using the molar mass of hydrated oxalic acid.