Temperature as a state property?

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Temperature as a state property?

Postby 204635822 » Sun Jan 17, 2016 12:37 pm

In lecture Dr. Lavelle said that temperature can be a state property because you can calculate the change in temperature without knowing how the heat changes. Then he said that heat is not always a state property. So is temperature a state property or not?

Joyce Xiong 4C
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Re: Temperature as a state property?

Postby Joyce Xiong 4C » Sun Jan 17, 2016 12:42 pm

Hi there!

From what I know, what you said was correct, that temperature is a state property and heat is only sometimes a heat property. The reason why heat is only sometimes a state property is because heat, when the pressure of the system is constant (enthalpy), is a state property, but is not a state property otherwise (when pressure is not constant). As for temperature, it is a state property; thus when we solve for the change of temperature, we can simple subtract Temp initial from Temp final. Similarly, for enthalpy (heat is a state property), you can solve the change is heat as Hfinal - H initial, but you cannot do that when the heat is not under constant pressure

Hope this somewhat helps

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Re: Temperature as a state property?

Postby remymink4J » Sun Jan 17, 2016 8:36 pm

TEMPERATURE is a state property, HEAT is not. For this, you have to remember that temperature and heat are two completely different things.

Temperature: indicates random motion of particles
Heat: the transfer of energy due to a difference in temperature.
(These came from page 22 of the Thermochemistry section in Dr. Lavelle's notes)

So for temperature, you can take 20 degrees and add another 20 degrees to figure out that the final product has 40 degrees. You don't need to know the pathway of how it got there, you just need to know that it did.

For heat, on the other hand, you may need to know the pathway/how the energy was transferred (not a simple addition/subtraction solution).

Hope this helped!

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