m = mass of water evaporated = 25 mg = 25 x 10⁻³ g = 25 x 10⁻³ x 10⁻³ kg = 25 x 10⁻⁶ kg
L = latent heat of fusion of water to vapor = 24 x 10⁵ J/kg
n = number of breaths in a minute = 12
Heat lost in a breath is given as
q = mL
Total heat lost in a minute is given as
Q = nq
Q = nmL
inserting the values
Q = (12) (25 x 10⁻⁶) (24 x 10⁵)
Q = 720 J/min
