entropy and enthalpy


by jpd5184
Tags: enthalpy, entropy
jpd5184
jpd5184 is offline
#1
Nov14-10, 02:23 PM
P: 76
1. The problem statement, all variables and given/known data

consider the decomposition of calcium carbonate: CaCO3(s) yields CaO(s) + CO2(g)

a) calculate delta H and delta S from standard thermodynamic data.
b) calculate delta G at 25.0C

2. Relevant equations

G = H - TS


3. The attempt at a solution

i added up all the thermodynamic data and got -2236 KJ/mol
now this is the delta G but for (a) im not given a temperature(is it 25C) and i have to solve for two variables. not sure what to do.
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jpd5184
jpd5184 is offline
#2
Nov14-10, 07:21 PM
P: 76
anybody please, can u at least get me started.
Zeppos10
Zeppos10 is offline
#3
Nov16-10, 07:50 AM
P: 83
1. list Hf values for CaCO3, CaO, CO2 (-1207,-635,-394 kJ/mole) (this is at 25C, 1 atm)
2. H(reaction)=SUM(r*Hf), where r= reaction-coefficient= negative for reactants)
3. similar for entropy.
4. use G=H-TS for the calculation of G(reaction)

kk727
kk727 is offline
#4
Nov16-10, 08:52 PM
P: 55

entropy and enthalpy


Delta H and Delta S Values:
http://chemtables.tk/
(click Entropy and Enthalpy Tab)

Use Products - Reactants with the values on the website above to determine the overall delta H and delta S.

(Values for Products) - (Values for Reactants)

Then, once you have delta S and delta H, you can use the formula you provided above to find delta G.

You can also verify that your delta G is correct by using the values in the chart to see if you come out with the same answer. Make sure that you keep your values consistent! Entropy is often in J/mol while the others are in kJ/mol.


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