The french chemists, pierre l. dulong and alexis t. petit, noted in 1819 that the molar heat capacity of many solids at ordinary temperatures is proportional to the number of atoms per formula unit of the solid. they quantified their observations in what is known as dulong and petit's rule, which says that the molar heat capacity, , of a solid can be expressed as =⋅ where is the number of atoms per formula unit and is the universal gas constant. the observed heat capacity per gram of a compound containing thallium and chlorine is 0.21 j·k−1·g−1 . use dulong and petit's rule to determine the empirical formula of the compound.

TlCl

Explanation:

The Dulong and Petit's rule is:

Cp = N*3R, where Cp is the heat capacity, N is the number of atoms in the molecule, and R is the gas constant (8.314 J/K.mol). Note that Cp has unity in gram and R in mol, so we need to transform Cp to unity in mol.

Let's suppose that the formula of the compound formed bt thallium (Tl) and chlorine (Cl) is TlCl, which has molar mass: 204.4 g/mol of Tl + 35.5 g/mol of Cl = 239.9 g/mol.

Cp observed = 0.21 J/K.g * 239.9 g/mol = 50.379 J/K.mol

For the compound, N = 2:

Cp theorical = 2*3*8.314 = 49.884 J/K.mol

For TlCl₂ the molar mass is: 204.4 + 2*35.5 = 275.4 g/mol

Cp observed = 0.21 * 275.4 = 57.834 J/K.mol

N = 3

Cp theorical = 3*3*8.314 = 74.826 J/K.mol

For Tl₂Cl the molar mass is: 2*204.4 + 35.5 = 444.3 g/mol

Cp observed = 0.21*444.3 = 93.303 J/K.mol

N = 3

Cp theorical = 3*3*8.314 = 74.826 J/K.mol

Note that the difference will be greater when there are more atoms in the compound, so the empirical formula must be TlCl which has the closest Cp observed and theoretical.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.