Specific Heat

[Mohit Pandey]

I am back!!!! :esmoking:

I was wondering whether specific heat is associated with magnitude of force of attraction between the molecules of the substance?

More heat is required for the substance with more force of attraction between the molecules? :naughty:

[Mercedes Benzene]

I am back!!!!

I was wondering whether specific heat is associated with magnitude of force of attraction between the molecules of the substance?

More heat is required for the substance with more force of attraction between the molecules?

 

Welcome back!

To answer your question, yes. Specific heat is partially associated with molecular forces.

Molecules that demonstrate hydrogen bonding often have higher specific heats than those without.

For example: ammonia, and water both have rather large specific heats, in part due to their hydrogen bonds with other moelcules.

[Bystander]

Welcome back!

To answer your question, yes. Specific heat is partially associated with molecular forces.

Molecules that demonstrate hydrogen bonding often have higher specific heats than those without.

For example: ammonia, and water both have rather large specific heats, in part due to their hydrogen bonds with other moelcules.

 

"WORNG."

 

Molar heat capacities depend upon the partitioning of 3N (N = number of atoms per molecule) degrees of freedom among translational, rotational, and vibrational modes possible for the molecule (1/2 RT per translational and rotational mode, and RT per vibration). Specific heat is molar heat capacity divided by relative molecular mass. Interatomic forces determine temperatures at which vibrational modes become "active," and fully saturated (resulting in bond dissociation).

 

See "equipartition principle."

[ronthepon]

That's for the ideal cases only. If it actually were that simple, then all gases with the same number of constituent atoms would have the same specific heats. That's not absolutely true, because there are discrepancies.

 

So basically, although it is not completely dependent upon the intermolecular forces, we can safely say that specific heat (molar, or otherwise) is affected by intermolecular forces.

 

Also, it's important to remember that ideal gases are assumed to have no intermolecular forces, other than when they 'physically collide', that is.

[Bystander]

That's for the ideal cases only.

 

Nerp --- ALL cases --- solids, liquids, gases, ideal and non-ideal.

 

If it actually were that simple, then all gases with the same number of constituent atoms would have the same specific heats.

 

It is"that simple (with some qualifications near assorted critical points)." "All gases with the same number of constituent atoms have the same" number of degrees of freedom; that may or may not translate to "the same specific heats."

 

That's not absolutely true, because there are discrepancies.

 

At sufficiently high T, and for conductors, one must also consider contributions from electronic states and populations of conduction bands.

 

So basically, although it is not completely dependent upon the intermolecular forces, we can safely say that specific heat (molar, or otherwise) is affected by intermolecular forces.

 

Right answer. Wrong road. You have three degrees of freedom per particle (atom, electron, EM mode in a cavity, whatever). Each degree of freedom contributes 1/2 RT^.mol^-1 to the heat capacity if the "particle" is "free," and RT if bound in a potential well (chemical bond, vdW and London forces, hindered intramolecular rotations, lattices, and so on). A particle with less energy than the well depth contributes RT per degree of freedom in the well (times a function of a characteristic temperature associated with the well potential function); once the particle energy exceeds well depth, it's "free," and the mode contributes only 1/2 RT.

 

Also, it's important to remember that ideal gases are assumed to have no intermolecular forces, other than when they 'physically collide', that is.

 

Not "assumed," defined. Being dimensionless (zero volume), they cannot collide.

 

Getting back to the OP, bond energies and force constants affect only the characteristic temperatures of the bond potential functions.

[Erasmus00]

Bystander, you have assumed (and rather condescendinly) that equiparition holds for all temperatures T. To borrow your tone, this is incredibly wrong.

 

Equipartition ONLY holds for CLASSICAL, QUADRATIC degrees of freedom. This is why at normal temperatures, we don't consider the vibrational degrees of freedom for a diatomic molecule: these degrees of freedom are quantum, at that level.

 

Similarly, we can also deal with forces or interactions described by terms that aren't quadratic in the Hamiltonian, and then we need to do some work.

 

Finally, Bystander, try to aim your answer to the question at the level of the person asking the question. Mercedes Benzene answered the question correctly, and in a much more understandable way: specific heat can certainly be effected by interatomic forces, and water and ammonia do have higher specific heats due, in part, to hydrogen bonding.

-Will

[Mercedes Benzene]

Bystander, you have assumed (and rather condescendinly) that equiparition holds for all temperatures T. To borrow your tone, this is incredibly wrong.

 

Equipartition ONLY holds for CLASSICAL, QUADRATIC degrees of freedom. This is why at normal temperatures, we don't consider the vibrational degrees of freedom for a diatomic molecule: these degrees of freedom are quantum, at that level.

 

Similarly, we can also deal with forces or interactions described by terms that aren't quadratic in the Hamiltonian, and then we need to do some work.

 

Finally, Bystander, try to aim your answer to the question at the level of the person asking the question. Mercedes Benzene answered the question correctly, and in a much more understandable way: specific heat can certainly be effected by interatomic forces, and water and ammonia do have higher specific heats due, in part, to hydrogen bonding.

-Will

 

Thank you so much!