# Entropy of the universe

## 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!

Last edited:

collinsmark
Homework Helper
Gold Member

## 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.

Sorry that 200 has been corrected to 300

collinsmark
Homework Helper
Gold Member
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. Sorry it's 2/9