Standard enthelpy of formation

In summary, the standard enthalpy of formation is the change in enthalpy that occurs when a compound is formed from its constituent elements in their standard states. It is measured under standard conditions of temperature and pressure using a calorimeter. This measurement is significant as it reflects the stability of the compound and can be used to calculate the enthalpy change of a reaction. The standard enthalpy of formation differs from the standard enthalpy of reaction, as the former is for the formation of a compound while the latter is for a specific chemical reaction. And finally, the standard enthalpy of formation can be negative, indicating a more stable compound and is often observed in exothermic reactions.
  • #1
Conductivity
87
3
So when they said that to produce water vapor at standard state it releases -241 KJ/mol
and liquid water -284 KJ/mol

You can't create water vapor at standard temperature but I assume they used Hess' law
Anyway, my question is when you change from water to vapor you need 44KJ/mol

So that would be the energy required to change from 25 C liquid to 25 C vapor.
Does it change for example when you want to change it from another temperature?
 
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  • #2
Yes. Do you know a formula for the variation of ΔH with temperature?
 

1. What is standard enthalpy of formation?

The standard enthalpy of formation is the change in enthalpy that occurs when one mole of a compound is formed from its constituent elements in their standard states.

2. How is standard enthalpy of formation measured?

Standard enthalpy of formation is measured under standard conditions of temperature (298 K) and pressure (1 atm) using a calorimeter.

3. What is the significance of standard enthalpy of formation?

The standard enthalpy of formation is a measure of the stability of a compound. It can also be used to calculate the enthalpy change of a reaction using Hess's Law.

4. How does standard enthalpy of formation differ from standard enthalpy of reaction?

Standard enthalpy of formation is the enthalpy change for the formation of a compound from its elements, while standard enthalpy of reaction is the enthalpy change for a specific chemical reaction.

5. Can standard enthalpy of formation be negative?

Yes, standard enthalpy of formation can be negative, indicating that the compound is more stable than its constituent elements. This is often the case for exothermic reactions.

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