Enthalpy: Why Does Temperatures Affect it?

  • Thread starter arjentje
  • Start date
In summary, the enthalpy of water decreases as the temperature rises because as heat energy is input, the enthalpy increases. However, this may seem counterintuitive since the volume of the water also increases, requiring more energy to evacuate that volume. This could potentially lead to confusion between enthalpy and entropy.
  • #1
arjentje
1
0
I'm breaking my mind on the next question. Why does the enthalpy of water lowers when the temperature rises?

I would say you input heat-energy, so the enthalpy rises. But this does not seem true...
 
Physics news on Phys.org
  • #2
i would dare say you have gotten your information wrongly. Once you heat anything, given that no chemical reaction occurs enthalpy will surely increase.

In case you need prove here's http://www.thermexcel.com/english/tables/eau_atm.htm" [Broken]
 
Last edited by a moderator:
  • #3
Maybe it was entropy?
 
  • #4
yeah, seems backwards.

As it was explained to me in my undergrad thermo class, enthalpy is the amount of energy you'd have to use to recreate the substance, including the energy needed to evacuate the volume occupied by the substance.

More volume (by heating) means that you're going to need to take into account a larger amount of energy to evacuate that volume.
 

1. What is enthalpy and how does it relate to temperature?

Enthalpy is a thermodynamic property that measures the total energy of a system. It takes into account both the internal energy and the work done by the system. Temperature affects enthalpy because as temperature increases, the internal energy of the system also increases, leading to a higher enthalpy.

2. Why does enthalpy change with temperature?

Enthalpy changes with temperature because temperature is a measure of the average kinetic energy of molecules in a system. As temperature increases, molecules have more energy and are able to move more freely, resulting in a higher enthalpy. Conversely, as temperature decreases, molecules have less energy and are more restricted in their movement, leading to a lower enthalpy.

3. How does enthalpy affect phase changes?

Enthalpy plays a crucial role in phase changes, such as melting, boiling, and condensation. During these processes, the enthalpy of the system changes due to the energy required to break or form intermolecular bonds. For example, when water is heated, its enthalpy increases until it reaches its boiling point, at which point the enthalpy remains constant as the energy is used to break intermolecular bonds and convert the liquid water into vapor.

4. Can enthalpy be negative?

Yes, enthalpy can be negative. This typically occurs when the system releases more energy than it absorbs, leading to a decrease in enthalpy. For example, when water freezes, it releases energy into the surroundings, resulting in a decrease in enthalpy.

5. How is enthalpy measured and expressed?

Enthalpy is typically measured in joules (J) or kilojoules (kJ). It is often expressed in terms of enthalpy change (ΔH), which is the difference between the initial enthalpy and the final enthalpy of a system. Enthalpy can also be expressed per unit mass (specific enthalpy) or per mole (molar enthalpy).

Similar threads

Replies
5
Views
276
  • Thermodynamics
Replies
2
Views
741
  • Introductory Physics Homework Help
Replies
12
Views
267
  • Introductory Physics Homework Help
Replies
9
Views
3K
  • Introductory Physics Homework Help
Replies
16
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
203
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
8
Views
395
  • Introductory Physics Homework Help
Replies
1
Views
558
  • Introductory Physics Homework Help
Replies
11
Views
1K
Back
Top