Entalpy Change: Pressure & Temperature Effects

  • Thread starter Thread starter yifan
  • Start date Start date
  • Tags Tags
    Change
AI Thread Summary
The discussion centers on the variability of enthalpy change in chemical reactions under different temperature and pressure conditions. Enthalpy, a state property, is influenced by temperature and pressure, as expressed in the equation H = U + PV, where U is internal energy, P is pressure, and V is volume. While enthalpy is relevant to reactions in open systems, it does not directly represent the energy of a chemical reaction. Instead, the PV term relates to work done during exothermic reactions, where energy can alter internal energy and perform work against atmospheric pressure. The energy associated with a specific reaction remains constant, but varying temperature and pressure can affect the amount of energy released, as these factors influence the frequency of individual reactions occurring.
yifan
Messages
8
Reaction score
0
Does anybody know why the entalpy change for a reaction differs in different pressure and temperature?
 
Chemistry news on Phys.org
enthalpy is a state property of a substance, like temperature and pressure
it also varies with temperature and pressure via H=U+PV
U is the internal energy, and you know what P and V are

so at different temps and pressures, a substance will have different enthalpies
this will change the deltaH in a reaction between two substances
 
Enthalpy pertains to reactions in open systems. To be truthful, enthalpy does not directly pertain to the energy of a chemical reaction, the PV which shrumeo mentioned relates to a separate work function...that is when a exothermic chemical reaction occurs, the energy can be used to change the internal energy U as well as expand against the atmosphere PV.

The energy of a specific chemical reaction is constant, and in most cases PV is considered negligible. Think bond energies.

Thus the enthalpy of the reaction does not change, rather different amounts of energy is released at different temperature and pressure since these two factors influence how many of such individual reactions take place.

----------
http://groups.msn.com/GeneralChemistryHomework
 
Last edited by a moderator:

Thread 'Humidity of a saturated NaCl solution with anticaking additive'

I want to test a humidity sensor with one or more saturated salt solutions. The table salt that I have on hand contains one of two anticaking agents, calcium silicate or sodium aluminosilicate. Will the presence of either of these additives (or iodine for that matter) significantly affect the equilibrium humidity? I searched and all the how-to-do-it guides did not address this question. One research paper I found reported that at 1.5% w/w calcium silicate increased the deliquescent point by...
View full post »

Similar threads

What does "limit of zero pressure" mean for ideal gas temperature?
Replies
14
Views
3K
Looking for a chemical with a boiling point between 10C and 50C
Replies
4
Views
2K
Does the initial temperature affect the change in temp?
Replies
13
Views
6K
Substance that boils at room temperature: Controlling the boiling temperature
Replies
12
Views
2K
Andrew's experiment on liquefaction of gases
Replies
3
Views
2K
Vapor pressure -- How does water still boil at 100°C in an open pot?
Replies
35
Views
5K
Role of pressure and temperature in chemical reactions
Replies
1
Views
2K
Show that Temperature remains unchanged in phase changes
Replies
8
Views
1K
Does pressure affect equilibrium vapor pressure (or RH)?
Replies
8
Views
3K
What is the difference between internal energy and enthalpy?
Replies
12
Views
3K

Hot Threads

Recent Insights

Back
Top