The ""steam"" above a freshly made cup of instant coffee is really water vapor droplets condensing after evaporating from the hot coffee. What is the final temperature of 250 g of hot coffee initially at 90.0ºC if 2.00 g evaporates from it

Heat is taken away from coffee by evaporating water in the process of turning into vapor. So coffee becomes cold

Heat taken up by water to evaporate

mass x latent heat

= 2 x 540 Calorie.

= 1080 Cals

If t be the decrease in temperature of coffee

heat given out

= mass x specific heat of water x fall in temperature

250 x 1 x t

heat loss = heat gain

250 t = 1080

t = 4.32 °C.

Final temp = 90 - 4.32 = 85.68 °C.