posted by Eric on .
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 280 g of hot coffee initially at 90.0°C if 2.50 g evaporates from it? The coffee is in a Styrofoam cup, and so other methods of heat transfer can be neglected. Assume that coffee has the same physical properties as water.
cM[t(ini) –t(fin)] = mr
cMΔt = mr
Δt= mr/cM= 2.5•10⁻³•2260•10³/4183•0.28 = 4.8℃
T(fin) = 90-4.8 = 85.2℃