Question

The energy required to increase the temperature of 180 g of liquid water from 10$^\circ$C to 15$^\circ$C is 3765 J. What is $C_p$ of water in J mol$^{-1}$ K$^{-1}$? ($H_2O$ = 18 u)

• A. 75.3
• B. 376.5
• C. 753
• D. 37.65

Hint:

Use $C_p = \dfrac{q}{n \cdot \Delta T}$ for constant pressure processes where $q$ is heat absorbed, $n$ is number of moles, and $\Delta T$ is change in temperature.

Answer 1

The Correct Option is A

Given: Mass = 180 g, $\Delta T = 5^\circ C$, Energy = 3765 J, Molar mass of water = 18 g/mol
Number of moles = $\dfrac{180}{18} = 10$ mol
$C_p = \dfrac{q}{n \cdot \Delta T} = \dfrac{3765}{10 \cdot 5} = \dfrac{3765}{50} = 75.3$ J mol$^{-1}$ K$^{-1}$