To calculate the entropy change (
ΔS) for the melting of sodium chloride (NaCl), we can use the formula:
ΔS = Q_rev / T
where:
- ΔS is the change in entropy (in J/K),
- Q_rev is the heat absorbed during the melting process (in joules),
- T is the absolute temperature (in Kelvin) at which the melting occurs.
First, we need to determine Q_rev for melting 25.6 g of NaCl. Given that the heat of fusion of NaCl is 517 J/g, we can calculate Q_rev as follows:
Q_rev = mass × heat of fusion
Q_rev = 25.6 g × 517 J/g = 13279.2 J
Next, we need to convert the melting point of NaCl from degrees Celsius to Kelvin. The melting point is 801 °C:
T = 801 + 273.15 = 1074.15 K
Now, we can calculate the change in entropy:
ΔS = Q_rev / T
ΔS = 13279.2 J / 1074.15 K ≈ 12.35 J/K
Therefore, the entropy change for the system when melting 25.6 g of sodium chloride is approximately 12.35 J/K.