Entropy. Energy Quality. You are offered 1000 J of energy. Would you rather have it as A) mechanical work B) frictional work C) heat from an object at 1000 K D) heat from an object at 300 K. A Carnot cycle found a relationship between the temperatures and heat.
The heat in and out are of opposite sign.Quantifying Quality
The latent heat of ice is 79.7 kcal/kg. and heat.
What is the change of entropy for a very slowly melting 1.00 kg piece of ice?
What is the change in entropy for the surroundings?
Find the heat transfer.
Q = mL = 79.9 kcal
Find the entropy change.
DS = Q/T = 0.292 kcal/K
The process is reversible.
DSsurr = -0.292 kcal/KMelting Ice
A sample of 50.0 kg water at 20.0 and heat.C is mixed with 50.0 kg water at 24 C.
Estimate the change in total entropy.
Find the heat transfer. There are equal amounts of heat in each sample.
Q = mcDT = 100. kcal
Find the entropy change in each sample using the average temperature.
DSH = Q/T = -100. kcal/296K = -0.338 kcal/K
DSL = Q/T = +100. kcal/294K = +0.340 kcal/K
The difference is the net change.
DS = +0.002 kcal/KMixing
The entropy of an isolated system never decreases. It only stays the same for reversible processes.