What is the enthalpy change when 25 g's of PCl5 are decomposed /\ H= 90
What's the /\H = 90?
To calculate the enthalpy change when PCl5 is decomposed, we need to use the formula:
ΔH = (ΔHf products) - (ΔHf reactant)
Given that the enthalpy change for the reaction (∆H) is 90 kJ and the reactant is PCl5, we need to find the enthalpy of formation (∆Hf) for PCl5.
1. Start by determining the molar mass of PCl5:
- Phosphorus (P) has an atomic mass of 31 grams/mol.
- Chlorine (Cl) has an atomic mass of 35.5 grams/mol.
Therefore, the molar mass of PCl5 is (31 + 5 * 35.5) grams/mol.
2. Calculate the number of moles of PCl5:
Divide the given mass of PCl5 (25 grams) by the molar mass obtained in step 1.
3. Find the enthalpy of formation of PCl5 (∆Hf PCl5):
Look up the ∆Hf value of PCl5 in a reliable reference source, such as a chemistry textbook or an online database. The ∆Hf value represents the enthalpy change when one mole of the compound is formed from its constituent elements in their standard states (usually at 25°C and 1 atm pressure).
4. Calculate the enthalpy change when 25 grams of PCl5 are decomposed (∆H):
Multiply the number of moles of PCl5 (obtained in step 2) by the ∆Hf value of PCl5 (obtained in step 3). This will give you the enthalpy change for the given mass of PCl5.
For example, let's say the ∆Hf value for PCl5 is -150 kJ/mol:
∆H = (ΔHf products) - (ΔHf reactant)
∆H = 0 - (-150)
∆H = 150 kJ
Therefore, if the ∆Hf value for PCl5 is -150 kJ/mol, the enthalpy change when 25 grams of PCl5 are decomposed (∆H) would be 150 kJ.