Phase Change and Heat Capacity

[leathersofa]

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Is there any relation between heat capacity and melting/boiling point? as in, does an object with higher heat capacity have stronger IMFs compared to an object with lower heat capacity?

 

[ashtonjam]

Is there any relation between heat capacity and melting/boiling point? as in, does an object with higher heat capacity have stronger IMFs compared to an object with lower heat capacity?

I don't believe there is any relationship between heat capacity and boiling point/melting point. At least that's what TBR says in their phases chapter.

On a temperature vs. time graph, heat capacity would be the slope of the line in between phase changes and phase changes would be the flat parts. A higher heat capacity would be a lower change in temperature over time, or a lower slope. That's as far as it goes, no IMFs really.

 

[leathersofa]

A higher heat capacity would be a lower change in temperature over time, or a lower slope. That's as far as it goes, no IMFs really.

but what about water?
water has a high heat capacity because of the presence of hydrogen bonds, which increase intermolecular forces between molecules
so wouldn't imfs play a role then?

thank you!

 

[ashtonjam]

but what about water?
water has a high heat capacity because of the presence of hydrogen bonds, which increase intermolecular forces between molecules
so wouldn't imfs play a role then?

thank you!

Fairly sure that IMFs are what determine the enthalpy of phase changes. That's when you're breaking hydrogen bonds between water, when going from ice to liquid, or liquid to gas. Heat capacity is what comes in between those phase changes and is determined by something other than IMFs.

Wikipedia has a short section on it. Specific heat capacity seems to be related to the degrees of freedom of motion in which energy can be stored (translational, rotational, vibrational). It doesn't mention IMFs.

EDIT: TBR also has a sentence on it that specifically says it's energy stored in vibrational motion.

The greater the amount of energy required to increase the vibrational energy of a substance, the greater its heat capacity.

 

[Romz]

but what about water?
water has a high heat capacity because of the presence of hydrogen bonds, which increase intermolecular forces between molecules
so wouldn't imfs play a role then?

thank you!

Hmm, I like this question. 👍

Heat capacity has to do with the amount of energy required to raise the temperature by one unit degree per unit mass. AKA, amount of energy needed to excite fluid.

Given two substances that boil at the same temperature, it is possible to see a disparity between their specific heats - all this means is that more temperature is required to raise one substances to their bp than another. Intramolecular forces do not have a direct correlation with specific heat. (Based on my google researching)

 

[leathersofa]

Hmm, I like this question. 👍

Heat capacity has to do with the amount of energy required to raise the temperature by one unit degree per unit mass. AKA, amount of energy needed to excite fluid.

Given two substances that boil at the same temperature, it is possible to see a disparity between their specific heats - all this means is that more temperature is required to raise one substances to their bp than another. Intramolecular forces do not have a direct correlation with specific heat. (Based on my google researching)

do you mean intermolecular forces (just to be sure)?

 

[leathersofa]

thank you everybody! i think i get it now:

1. heat capacity is not dictated by imfs, rather by energy of motion
2. phase changes are connected with imfs
3. phase changes and heat capacity do not influence each other since the properties of heat capacity are not dictated by imfs.

is this right? thanks!