High School

If the molar heat of fusion of a certain substance is 5000 J/mol and the entropy of fusion is 50 J/mol·K, then the melting temperature is:

a. -273 degrees Celsius
b. -173 degrees Celsius
c. impossible to determine from the data
d. 173 degrees Celsius
e. 100 degrees Celsius
f. 273 degrees Celsius

Answer :

The correct answer is f. 273 degrees Celsius.

The melting temperature is approximately 173 degrees Celsius.

The molar heat of fusion refers to the amount of heat energy required to convert one mole of a substance from solid to liquid at a constant temperature. In this case, the molar heat of fusion is given as 5000 J/mol.

The entropy of fusion, on the other hand, measures the change in randomness or disorder that occurs during the process of fusion. It is given as 50 J/molk.

To find the melting temperature, we need to use the formula:

ΔG = ΔH - TΔS

where ΔG is the change in Gibbs free energy, ΔH is the enthalpy change (molar heat of fusion), T is the temperature in Kelvin, and ΔS is the change in entropy.

At the melting point, the Gibbs free energy change is zero, so we can set ΔG to zero in the equation above:

0 = 5000 J/mol - T(50 J/molk)

Now, let's solve for T:

5000 J/mol = T(50 J/molk)

T = 5000 J/mol / 50 J/molk

T = 100 K

To convert from Kelvin to Celsius, we subtract 273.15:

T = 100 K - 273.15

T ≈ -173 degrees Celsius

However, since the question asks for the melting temperature and not the freezing temperature, we need to take the positive value:

T ≈ 173 degrees Celsius

Therefore, the melting temperature is approximately 173 degrees Celsius.

In conclusion, the correct answer is d. 173 degrees Celsius.

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