Understanding Enthalpy of Formation
The enthalpy of formation (ΔHf°) is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states under standard conditions (usually 25°C and 1 atm).
Writing the Equation
1. Identify the Elements: Ethanol is formed from carbon (C), hydrogen (H₂), and oxygen (O₂).
2. Standard States:
* Carbon exists as solid graphite (C(s)).
* Hydrogen exists as diatomic gas (H₂(g)).
* Oxygen exists as diatomic gas (O₂(g)).
3. Balance the Equation:
```
2 C(s) + 3 H₂(g) + 1/2 O₂(g) → C₂H₅OH(l)
```
Enthalpy Change (ΔHf°)
The enthalpy of formation of ethanol is the enthalpy change (ΔH) associated with this reaction. It is usually expressed in units of kJ/mol. You can look up the standard enthalpy of formation of ethanol in a table of thermodynamic data.
Important Notes:
* Standard States: Always make sure to use the standard states of the elements.
* States of Matter: Include the states of matter (s, l, g, aq) for each substance.
* Coefficient: The coefficient of ethanol must be 1 mole as per the definition of enthalpy of formation.
* Enthalpy of Formation is a Specific Value: The enthalpy of formation is a specific value for a compound and is usually given in thermodynamic data tables.
Let me know if you have any other questions!
