What is the heat of formation value for AQUEOUS phosphoric acid (H3PO4)? I can only find it for liquid. thank you
To find the heat of formation value for aqueous phosphoric acid (H3PO4), you may need to use Hess's Law or conduct a calorimetric experiment. Since the heat of formation of a substance generally refers to a chemical reaction in the gas phase, it can be challenging to find the exact value for a specific compound in a particular state, such as aqueous.
Here are a couple of approaches you can take to estimate the heat of formation of aqueous phosphoric acid (H3PO4):
1. Use Hess's Law:
- Look for the heat of formation values of the reactants and products involved in the formation of H3PO4. These values are typically available.
- H3PO4 can be made from the combination of phosphorus pentoxide (P4O10) and water (H2O):
P4O10 (s) + 6 H2O (l) -> 4 H3PO4 (aq)
2. Conduct a calorimetric experiment:
- Perform a reaction between known amounts of phosphorus pentoxide (P4O10) and water (H2O) to produce aqueous phosphoric acid (H3PO4). Measure and record the heat evolved or absorbed during the process using a calorimeter.
- This measured heat can be used to calculate the heat of formation of aqueous phosphoric acid (H3PO4) using the equation: ΔH = q / n, where ΔH is the heat of formation, q is the measured heat, and n is the number of moles of the substance.
It's important to note that the heat of formation values can vary depending on the reference states and conditions used. Therefore, it might be challenging to find an exact value for aqueous phosphoric acid (H3PO4).