Question

The internal energy (in J) when 90 g of water undergoes complete evaporation at 100°C is ______.

(Given ΔH_vap for water at 373 K = 41 kJ/mol, R = 8.314 JK⁻¹ mol⁻¹)

Options

• 150250

• 167800

• 189494

• 190000

Answer 1

The internal energy (in J) when 90 g of water undergoes complete evaporation at 100°C is 189494.

Explanation:

No. of moles of H₂O = `(90  "g")/(18  "g mol"^-1)` = 5 mol

ΔH = ΔU + Δn_gRT

⇒ 41000 × 5 J = ΔU + 5 mole × 8.3145 mol⁻¹ K⁻¹ × 373 K

⇒ 205000 J = ΔU + 15505.61 J

⇒ ΔU = 189494.39 J

= 189494 J