90 g of water spilled out from a vessel in the room on the floor. Assuming that water vapour behaving as an ideal gas, calculate the internal energy change when the spilled water undergoes complete evaporation at `100^(@)C`. (Given the molar enthalpy of vaporisation of water at 1 bar and 373 K = 41 kJ `mol^(-1)`).

Explanation

To calculate the internal energy change (ΔU) when 90 g of water evaporates at 100°C, we can follow these steps:

### Step 1: Calculate the number of moles of water
The molar mass of water (H2O) is approximately 18 g/mol. To find the number of moles (n) of 90 g of water, we use the formula:

\[ n = \frac{\text{mass}}{\text{molar mass}} = \frac{90 \text{ g}}{18 \text{ g/mol}} = 5 \text{ moles} \]
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