June 07, 2020, 02:15:20 AM
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### Topic: Entropy/Enthalpy  (Read 199 times)

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#### Diamond724

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##### Entropy/Enthalpy
« on: May 16, 2020, 05:19:41 PM »
Hi! I'm currently writing an essay and part of it is showing the complete change in entropy and enthalpy using equations. I understand how to find out if it's positive & increasing but not the exact numbers and equations. Could anyone help out?

Here's the equation I'm using:

C3H8(g) + 5 O2(g) = 3 CO2(g) + 4 H2O(g)

Thanks!

#### MNIO

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##### Re: Entropy/Enthalpy
« Reply #1 on: May 16, 2020, 10:07:54 PM »
If I were to tell you dHrxn = dHformation products - dHformation reactants
(1) do you think you could find dHf products and dHf reactants via google?
(2) how would the coefficients factor in?
(3) how do you suppose entropy works?

#### Diamond724

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##### Re: Entropy/Enthalpy
« Reply #2 on: May 16, 2020, 10:57:59 PM »
(1) do you think you could find dHf products and dHf reactants via google?
I think so, i'm not sure if i'm correct though. To clarify, is this equation what you are talking about? ΔH°rxn = Σ ΔH°f (products) − Σ ΔH°f (reactants)

(2) how would the coefficients factor in?
That would be how many molecules you have of that element, right? I assume it would need to be multiplied by the "dHf reactants and products" you were talking about.

(3) how do you suppose entropy works?
Entropy measures the amount of heat transferred during a reaction from what I was told, if that's the answer your're looking for.

Online school is so much harder to learn than real life haha. Took it for granted...
« Last Edit: May 16, 2020, 11:40:56 PM by Diamond724 »

#### MNIO

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##### Re: Entropy/Enthalpy
« Reply #3 on: May 18, 2020, 02:06:17 PM »
for the reaction
aA + bB ---> cC + dD
dH = dHf products - dHf reactants
= c*dHf of C + d*dHf of D - a*dHf of A - b*dHf of B

look at sites like this
https://www.engineeringtoolbox.com/standard-state-enthalpy-formation-definition-value-Gibbs-free-energy-entropy-molar-heat-capacity-d_1978.html

try the same thing with entropy