ΔS is positive for which one of the following reactions?
Ag+(aq) + Cl- (aq) = AgCl(s)
N2(g) + 3H2(g) = 2NH3(g)
CaO(s) + CO2(g) = CaCO3(s)
2SO3(g) = 2SO2(g) + O2(g)
H2O(l) = H2O(s)
Same question here. Which do you think move from more random to less random and why?
For example, #4 is more random because there are more moles gas on the right than left. #5 is less random because the molecules in liquid water are more free to move around than in ice where they are more or less locked in place. So dS increases in #4 and decreases in #5. dS is + for #4 and - for #5.
To determine whether ΔS (change in entropy) is positive or negative for a given reaction, you need to consider the entropy changes associated with the reactants and products.
The general rule is that ΔS is positive if the disorder or randomness of the system increases, and negative if the disorder decreases. Here's how you can analyze each reaction to determine the sign of ΔS:
1. Ag+(aq) + Cl-(aq) = AgCl(s):
In this reaction, ions in the aqueous phase come together to form a solid compound. The migration of ions from the solution to the solid state reduces disorder, so ΔS is negative.
2. N2(g) + 3H2(g) = 2NH3(g):
The reaction involves gaseous reactants and a gaseous product. Here, the number of gas moles increases from 4 (N2 + 3H2) to 2 (2NH3). Since increasing the number of gas moles generally leads to increased disorder, ΔS is positive.
3. CaO(s) + CO2(g) = CaCO3(s):
In this reaction, a solid and a gas react to form a different solid. The change from a gas to a solid state decreases disorder, so ΔS is negative.
4. 2SO3(g) = 2SO2(g) + O2(g):
This reaction involves the decomposition of SO3 gas into SO2 gas and O2 gas. The number of gas moles increases from 2 to 3, leading to an increase in disorder. Hence, ΔS is positive.
5. H2O(l) = H2O(s):
The transition from liquid water to solid ice involves the arrangement of water molecules into a more ordered structure, resulting in a decrease in disorder. Thus, ΔS is negative.
Therefore, the reaction with a positive ΔS is N2(g) + 3H2(g) = 2NH3(g).