ThermodynamicsMedium

Question

The correct order of molar heat capacities measured at 298 K and 1 bar is :

Options

A.Copper (s) $>$ Bromine (l) $>$ Helium (g)
B.Bromine (l) > Copper (s) > Helium (g)
C.Helium (g) $>$ Bromine (l) $>$ Copper (s)
D.Helium (g) > Bromine (l) = Copper (s)

Solution

Sol. [Key Concept: Molar heat capacity: liquids $>$ solids (more degrees of freedom) $>$ monatomic gas (only translational), giving ${Br}_{2}(l) > Cu(s) > He(g)$.]

Generally molar heat capacity of liquids is greater than solids because liquids have greater degrees of freedom & thus can store more energy with lesser temperature rise.

Also for monoatomic gases molar heat capacity is low as only transalational degrees of freedom are present.

∴ order is :

$${Br}_{2}(\mathcal{l}) > Cu(s) > He(g) $$

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