Freezing is the reverse of fusion, so $\Delta H_{freezing} = -\Delta H_{fusion} = -6$ kJ/mol. Moles of water = 1g / 18 g/mol. Enthalpy change = $(-6 	ext{ kJ/mol}) 	imes (1/18 	ext{ mol}) = -1/3 	ext{ kJ} approx -0.33$ kJ.