How Does Heat Transfer Between Two Reservoirs Affect Universal Entropy?

[gboff21]

Homework Statement

Two large reservoirs, H and C, are available: if H is at 900 K and C is at 300 K, what is the
entropy change of the Universe if 100 J of heat are taken from H and added to C?

Homework Equations

ΔS=∫dQ/T

ΔS_universe = ΔS_surroundings + ΔS_system

The Attempt at a Solution

so it's just (-100/900)+(100/300) = 9/2 right? Just checking!

 

[collinsmark]

Homework Statement

Two large reservoirs, H and C, are available: if H is at 900 K and C is at 300 K, what is the
entropy change of the Universe if 100 J of heat are taken from H and added to C?

Homework Equations

ΔS=∫dQ/T

ΔS_universe = ΔS_surroundings + ΔS_system

The Attempt at a Solution

so it's just (-100/900)+(100/200)

I think that's the right approach. But isn't C at 300 K (not 200)?

= 9/2 right? Just checking!

I think you might have inverted something.

 

[gboff21]

Sorry that 200 has been corrected to 300

 

[collinsmark]

Sorry that 200 has been corrected to 300

Okay, so we have...

so it's just (-100/900)+(100/300)

Okay, that looks correct.

= 9/2 right?

Wait, what?

Try that simplification one more time.

 

[gboff21]

Sorry it's 2/9