# Entropy - A2 chem AQAWatch

Thread starter 7 years ago
#1
Are standard entropy and entropy of a system the same thing?

DeltaS = Sproducts-Sreactants

I'm getting confused, because i'm using two books each using slightly different terms, but are these the same thing?

Also, should free energy change be given in KJmol^-1 or just Jmol^-1
Again, I have two books saying two different things.
0
7 years ago
#2
(Original post by J_Hunter)
Are standard entropy and entropy of a system the same thing?

DeltaS = Sproducts-Sreactants

I'm getting confused, because i'm using two books each using slightly different terms, but are these the same thing?

Also, should free energy change be given in KJmol^-1 or just Jmol^-1
Again, I have two books saying two different things.
Not really clear what you are asking.

Standard entropy of a substance is a characteristic of that substance measured under standard conditions.

The entropy change referes to the before and after of some process - it is the difference in standard entropy of the before and after.

Free energy can be given in kJ or J and may or not be per mole depending on the change in question.
0
Thread starter 7 years ago
#3
(Original post by charco)
Not really clear what you are asking.

Standard entropy of a substance is a characteristic of that substance measured under standard conditions.

The entropy change referes to the before and after of some process - it is the difference in standard entropy of the before and after.

Free energy can be given in kJ or J and may or not be per mole depending on the change in question.

Looking at a past paper question and mark scheme. The question was work out the standard enthalpy, standard entropy and free energy change for this reaction at 298K

For the the standard entropy, the mark scheme uses the formula
Sproducts-Sreactants
But in the chemistry book that I've been revising from, this formula has been used to work the enthalpy of a system. So I was wondering if these are exactly the same thing.
0
7 years ago
#4
(Original post by J_Hunter)
Looking at a past paper question and mark scheme. The question was work out the standard enthalpy, standard entropy and free energy change for this reaction at 298K

For the the standard entropy, the mark scheme uses the formula
Sproducts-Sreactants
But in the chemistry book that I've been revising from, this formula has been used to work the enthalpy of a system. So I was wondering if these are exactly the same thing.
No, they are very different things.

Entropy is a measure of the degree of disorder of a system, it is a function of the number of particles and their number of possible arrangements of energy over these particles.

The enthalpy change is the difference in internal potental energy between reactants and products which is manifest as a change in heat.

Enthalpy does not have absolute values - it can be found as a change in the system by measuring the heat lost or gained.
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Thread starter 7 years ago
#5
(Original post by charco)
No, they are very different things.

Entropy is a measure of the degree of disorder of a system, it is a function of the number of particles and their number of possible arrangements of energy over these particles.

The enthalpy change is the difference in internal potental energy between reactants and products which is manifest as a change in heat.

Enthalpy does not have absolute values - it can be found as a change in the system by measuring the heat lost or gained.
Oh, sorry about that. I mistyped that. I meant to say
"this formula has been used to work the Entropy of a system"
Not enthalpy
0
7 years ago
#6
(Original post by J_Hunter)
Oh, sorry about that. I mistyped that. I meant to say
"this formula has been used to work the Entropy of a system"
Not enthalpy
It doesn't change much of what I said.

The formula works out the change in entropy of a system, i.e. the difference between the absolute entropy of the products and that of the reactants.
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