Question

What is the enthalpy change (in J) for converting 9 g of H\(_2\)O (l) at \( +10^\circ C \) to H\(_2\)O (l) at \( +20^\circ C \)? Given \( C_p \) of water = 75 J/mol K and density of water = 1 g/mL.

• A. \( 750 \)
• B. \( 75 \)
• C. \( 37.5 \)
• D. \( 375 \)

Hint:

For heating a liquid, use \( q = nC_p \Delta T \), where \( n \) is moles, \( C_p \) is specific heat, and \( \Delta T \) is temperature change.

Answer 1

The Correct Option is D

Step 1: Moles of Water Molar mass of \( H_2O \) = 18 g/mol. \[ \text{Moles of water} = \frac{9}{18} = 0.5 \text{ mol} \]
Step 2: Heat Energy Required \[ q = n C_p \Delta T \] \[ q = (0.5) \times (75) \times (20 - 10) \] \[ = 0.5 \times 75 \times 10 = 375 \text{ J} \]