Please include a basic explanation with the answers Determine the entropy change

Question

Please include a basic explanation with the answers

Determine the entropy changes in the situations below, explaining your reasoning carefully. A 10omega resistor, in thermal contact with a reservoir, is held at a temperature of 300 K. A current of 5 A is passed through the resistor for 2 minutes. Ignoring changes in the source of the current, determine the change of entropy (i) in the resistor (ii) in the universe. A block of lead of heat capacity 1 kJK-1 is cooled from 300 K in to 100 K in two ways: (i) by plunging into a large liquid bath at 100 K (ii) by cooling first in a liquid bath at 200 K and then to 100 K in another bath. What is the entropy change of lead block and the universe in each case?

Explanation / Answer

a)

Heat produced by due to current flow in resistor = I^2*R*t

=5^2*10*2*60

=30000 J

i)

so,

Entropy change of resistor = -dQ/T = -30000/300 = 100 J/K

ii)

Entropy change of universe = - entropy of resistor = -100 J/K

b)

i)

entropy change of block = Cp*ln(T/To)

=1*10^3*ln(100/300)

=-1098.612 J/K

so,

entropy change of univerase = 1098.612 J/K

ii)

entropy change of block = Cp*[ln(T1/To)+ln(T2/T1)]

=1*10^3*[ln(200/300)+ln(100/200)]

=-1098.612

so,

entropy change of universe = 1098.612 J/K

here u can see that entropy is a state function, it's independent of path

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---