Using the specific heat of any substance

[Tush]

Ques 1) In determining and then using the specific heat of any substance:-
For solids and liquids, we usually assume that the sample is under constant pressure during the transfer, or at constant volume while the heat is absorbed. Then is it possible that the thermal expansion of the sample can be prevented by applying external pressure ?

Ques 2) Why it is that the specific heats under constant pressure and constant volume for any solid or liquid differ usually by no more than a few percent, where as gases have different values for their specific heats under constant pressure and constant volume ?

Ques 3) Generally , thermal expansion of gases is greater than that of solids and liquids . But this is true at any temperature (though the thermal expansion coefficient depends slightly on temperature) ? Is it due to the fact that the state of randomness for gas is much higher than that for liquid or gas.

 

[Naty1]

Try reading here:
http://en.wikipedia.org/wiki/Specific_heat#Factors_that_affect_specific_heat_capacity

Ques 1) of course

Ques 2) pressure has little effect on solids and liquids...

Ques 3) is thermal expansion proportional to randomness?? unsure...
Likely what you want is related to this...
http://en.wikipedia.org/wiki/Entropy#Order_and_disorder

but I did not follow up enough to see a unmistakable answer...

 

[Ali Inam]

Firstly,

YES, for the first question of yours and for the 2nd one, I would say that on liquids and solids, we don't have very large impacts of pressure if we compare that pressure to be implemented on gases.

Ah,

Not really sure about the 3rd question of yours !

 

[Mapes]

Regarding question 3: solids and liquids don't expand much with temperature because their atoms are confined by the electrostatic bonds that hold these substances together. The atoms or molecules in gases aren't collectively bonded together, and so higher temperatures produce higher velocities and thus large increases in volume for systems maintained at constant pressure (and thermal expansion is defined as the increase in V with T at constant P).

 

[sardar]

I can provide the following responses to the questions asked:

1) In determining and using the specific heat of any substance, it is important to consider the conditions under which the heat transfer is taking place. For solids and liquids, it is usually assumed that the sample is under constant pressure or constant volume. This is because changes in pressure can affect the volume of the substance, which in turn can affect the specific heat. However, it is possible to prevent thermal expansion of a sample by applying external pressure. This can be done by using a closed system where the sample is contained and the pressure can be controlled.

2) The difference in specific heats under constant pressure and constant volume for solids and liquids is usually small, while for gases it can be significant. This is because gases have a higher degree of freedom and can expand more easily compared to solids and liquids. Additionally, the specific heat of a substance is affected by its molecular structure, so gases with different molecular structures will have different specific heats under constant pressure and constant volume.

3) The thermal expansion of gases is generally greater than that of solids and liquids due to the higher degree of randomness in their molecular structure. This randomness allows the molecules to move more freely and expand when heated. However, the thermal expansion coefficient of gases can vary slightly with temperature, as the molecular structure and interactions can change with temperature. This is not necessarily related to the state of randomness, but rather the molecular properties of the gas.