# Relation between system enthalpy and surrounding entropy

1. Apr 19, 2015

### mooncrater

1. The problem statement, all variables and given/known data
It is given in my book that:
ΔStotal=ΔSsystem+ΔSsurrounding
Where S is entropy.
ΔSsurr=-ΔH/T
Therefore:
ΔStotal=ΔSsystem+[-ΔHsystem/T]

As we can see here that ΔSsurrounding=-ΔHsystem/T
is applied here . But is this relation correct?

2. Relevant equations
ΔS=qreversible/T
Where qreversible is the heat input which is equal to ΔH(enthalpy) for constant P and T.

3. The attempt at a solution
What I think is that , instead of ΔHsystem there should be ΔHsurroundings
Since the change in entropy of surroundings is taken. Am I correct here?

2. Apr 19, 2015

### Vatsal Sanjay

You you consider system plus the surrounding to be an isolated system and apply conservation of energy, you will find the relation between ΔHsystem and ΔHsurrounding
By the way you are correct here-
And they have not used ΔHsystem instead of ΔHsurrounding They have made use of the energy conservation equation I am talking about.

3. Apr 19, 2015

### mooncrater

I think the relation you're talking about is
ΔHsystem=-ΔHsurroundings
If energy is taken from the surroundings to the system.
Therefore when:
ΔSsystem=ΔHsystem/T will be equal to minus of ΔHsurroundings
/T
Am I correct here?

4. Apr 19, 2015

### Vatsal Sanjay

Yes you're correct