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Specific Heat and its relevance to Molecular Configuration

  1. Sep 24, 2015 #1
    Hello, this is one of the problems in my laboratory manual and it has been killing me. I've been working on this all week. It's due tonight, so hopefully it's not too late...

    1. The problem statement, all variables and given/known data

    Explain why specific heat is "specific", and how it gives a relative indication of molecular configuration and bonding.

    2. Relevant equations
    None.

    3. The attempt at a solution
    I already know why specific heat is "specific", that part of the solution is not a problem. What makes specific heat “specific” is that it is characteristic to the material or element in question. Heat Capacity is the amount of heat per change in temperature and it refers to the larger scheme of things. Two systems made of the same material will have the same specific heat, but their heat capacity varies with mass. If one system is twice as large as another, then its heat capacity is also twice as large; however, if they are composed of the same material, then each unit mass of the larger system possesses the same specific heat as a unit mass of the smaller system.

    As for the second part of the question:

    I was thinking, perhaps, it had to do with the degrees of freedom: a single atom has translational freedom (the ability to move on all three axis, xyz), a molecule of two atoms has translational and rotational freedom (spinning about its axis) and more complex molecules have the addition of oscillatory motions. Each of these movements are triggered after achieving a certain amount of energy. The degrees of freedom describe the different ways a molecule can store energy. So, the more degrees of freedom (f) a molecule has, the higher their specific heat? Do the degrees of freedom apply to subatomic particles like electrons and protons? If so, it doesn't make sense.

    According to the Periodic Table of Elements, Hydrogen possess the highest specific heat (14.4 J/gK). This is curious because H is also the smallest element with 1 proton and 1 electron. I also noticed that, generally, specific heat appears to decrease as you go down the Periodic Table, with Radon and Actinium tied at 0.092 J/gK.

    If heat is the kinetic motion of atoms and specific heat dictates how much energy is required to raise the temperature of a unit mass of that atom by one degree, then is the specific heat smaller for larger elements because they're larger? The larger an element, the more protons and electrons it has, which means it has the potential of producing the most kinetic energy per unit mass. Since Hydrogen is the smallest and most singular element, it makes sense that more energy is required to raise its temperature, because it only has 1 proton and 1 electron; thus, the lowest kinetic energy per unit mass.

    Speculating further, in chemistry, heat is a catalyst used to accelerate chemical reactions. The more energy added to a substance, the easier they can form and break bonds. What's more, it takes more energy to break a bond than it does to form a bond. Could it be that bond strength dictates specific heat? If the bonds of a molecule A are stronger than molecule B, then less energy is required to break the bonds of B than it does for A. In other words, the specific heat of B is smaller than A.

    Going back to subatomic particles, bonds are formed by the ceding, gaining, or sharing of electrons. The harder it is to remove an electron from an atom, the more energy required to remove it? Improbable. Although it makes sense intuitively, it just doesn't hold up after further scrutiny. By this logic, Hydrogen should have the least specific heat. Because the goal of every element is to reach equilibrium (octet rule), H is the most eager element because it can reach the equilibrium state by ceding its only electron or gaining another. Consequently, according to this logic, Noble Gases should have the highest specific heat because they are the less reactive elements on the Periodic Table. They already reached equilibrium, they don't want anything to do with other elements. However, Radon, a Noble Gas, has the smallest specific heat. Therefore, specific heat can't be related to the bonding of atoms in this sense.
     
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  3. Sep 24, 2015 #2

    SteamKing

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    Specific heat is 'specific' because it is the heat required to raise the temperature of a unit mass of a material by one degree.

    Similarly, the specific volume of a substance is the volume occupied by a unit mass of that substance.
     
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