Marcela dissolves 80.0 g of ammonium nitrate in 50.0 mL of water at room temperature and notes that the temperature of the solution decreases by 5.0°C.
Which correctly designates the signs of changes of G, S and H for this reaction?
Do you have thoughts on this? It seems obvious to me that delta H is +.
NH4NO3(s) + H2O ==> NH4NO3(aq) - heat
choices
A. H>0, S>0 , G<0
B. H<0, S>0 , G<0
C. H>0, S>0 , G>0
D. H<0, S<0 , G>0
https://answers.yahoo.com/question/index?qid=20091202141141AAzWAa6
Answers are not in the same order but you get the full explanation here.
To determine the signs of changes in Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH) for this reaction, we need to be aware of the overall process involved.
In this case, when ammonium nitrate dissolves in water, the temperature decreases, indicating an endothermic process (heat is absorbed from the surroundings).
Now, let's break down the signs of changes for the various thermodynamic parameters:
1. Enthalpy (ΔH):
- Since the process is endothermic (temperature decreases), ΔH will be positive (+) because heat is absorbed from the surroundings.
2. Entropy (ΔS):
- The dissolution of a solid in a liquid usually leads to increased disorder (entropy). In this case, since the ions of ammonium nitrate are dissociating into water molecules, it generally results in an increase in disorder. Therefore, ΔS will be positive (+).
3. Gibbs Free Energy (ΔG):
- ΔG is related to the changes in both enthalpy (ΔH) and entropy (ΔS) through the equation:
ΔG = ΔH - TΔS
- Since ΔH is positive (+) and ΔS is positive (+), the value of T (temperature in Kelvin) will determine the sign of ΔG. As the temperature decreases (from the dissolving process), TΔS will become more negative (-), which will make ΔG more positive (+).
In summary:
- ΔH: positive (+) as heat is absorbed
- ΔS: positive (+) due to increased disorder
- ΔG: more positive (+) as the temperature decreases
Therefore, the correct designations for the signs of changes of G, S, and H for this reaction are:
ΔG: positive (+)
ΔS: positive (+)
ΔH: positive (+)