About heat

[prasna]

What is latent heat and how is it different from specific heat?

[swansont]

If you add energy, things tend to increase in temperature, but T is a measure of translational KE of the center-of-mass only. Some energy gets "stored" in other places, like rotational states. So the specific heat tells you how much energy you have to add to raise the temperature a given amount.

 

When you undergo a phase change, additional energy is involved in forming/breaking of molecular bonds without seeing a change in temperature. This is the latent heat.

[Primarygun]

I put down a definition here.

Specific latent heat (of fusion or of vaporization) is the amount of energy required to convert 1kg of a substance from one state to another.

Specific heat capacity is the amount of energy required to change 1kg of a substance through 1 degree Celsius.

Note: the unit may differ in some regions.

[J.C.MacSwell]

If you add energy' date=' things tend to increase in temperature, but T is a measure of translational KE of the center-of-mass only. Some energy gets "stored" in other places, like rotational states. So the specific heat tells you how much energy you have to add to raise the temperature a given amount.

 

[b']When you undergo a phase change, additional energy is involved in forming/breaking of molecular bonds without seeing a change in temperature. [/b] This is the latent heat.

 

Can this also be considered an endothermic/exothermic chemical reaction?

 

Also, why does water have such a high specific heat?

[swansont]

Can this also be considered an endothermic/exothermic chemical reaction?

 

Also' date=' why does water have such a high specific heat?[/quote']

 

It's not a chemical reaction. The forces/bonds are between the molecules, not within them, so there is no change in the chemical composition.

 

AFAIK water has a high specific heat because it has many rotational and vibrational modes in which it can store energy, and has a small mass. I think being triatomic has something to do with it - you don't get certain modes in diatomic molecules. And since it's mich lighter than most metals, you get more molecules per gram in which you can store energy. Lithium, however, has a specific heat capacity almost as large - it has a very small mass.

[DQW]

The high specific heat capacity of Li is due to Dulong and Petit (in a crystalline solid the number of available modes is constant).

 

The high specific heat of water is essentially due to the fact that it is one of the lightest non-linear molecules. As far as I know, only ammonia (NH3), has a higher specific heat at RT - as is expected.

[DQW]

I think being triatomic has something to do with it - you don't get certain modes in diatomic molecules.

In diatomic (and linear triatomic) molecules, the moment of inertia about the internuclear axis is negligible.