# Entropy and enthalpy

1. Nov 14, 2010

### jpd5184

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.

2. Nov 14, 2010

### jpd5184

anybody please, can u at least get me started.

3. Nov 16, 2010

### Zeppos10

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)

4. Nov 16, 2010

### kk727

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.