The heat of dissolution is the heat change associated with the dissolution of a substance in a solvent. For lithium chloride (LiCl), the process is exothermic, meaning it releases heat.
The formula to calculate the heat of dissolution is:
\[ \Delta H_{\text{dissolution}} = - \frac{q}{n} \]
Where \( q \) is the heat absorbed or released, and \( n \) is the number of moles of LiCl.
Consider dissolving 8.0 g of LiCl in 100 mL of water, with the temperature increasing from 25°C to 38°C:
Using the formula:
\[ \Delta T = 38 - 25 = 13 \, \text{°C} \]
\[ q = 100 \times 4.18 \times 13 = 5434 \, \text{J} \]
\[ n = \frac{8.0}{42.39} = 0.189 \, \text{mol} \]
\[ \Delta H_{\text{dissolution}} = - \frac{5434}{0.189} = -28768 \, \text{J/mol} \approx -28.8 \, \text{kJ/mol} \]