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When comparing two different molecules, you have to look at the the total number of microstates that can be generated for each molecule along with the rigidity of the bonds within each molecule. A molecule with more bonds and more elements will usually have a higher entropy. If two molecules have the same number of atoms you have to look at which molecule has the most variety of atoms. For example, CO and N2 both have the same number of molecules but because CO can take on two different arrangements (O-C or C-O) it is said to have higher molar entropy than N2 because N2 can only be arranged as N-N. Another thing to look at when determining which molecule has a higher molar entropy is the physical state of the molecule. Typically, the standard molar entropies of gases are higher than hose of comparable solids and liquids at the same temperature. This type of entropy has been discussed in class and can be easily calculated when given the "S subscript M" of a certain molecule.
First try to look at the overall mass of the molecule; the molecule with more atoms will likely have more entropy. Then, if they have the same number, look at the variety of atoms; different types of atoms allow or different positions to be made (positional disorder increases --> entropy increases). You can also look at the shape of the molecules; the shape/structure that is the most flexible / less rigid will have more molar entropy.
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