Question

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

Answer 1

Answer:

Explanation:

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.