Can someone check this for me?
Predict which reactions are spontaneous:
a) Zn(s) + 2H+(aq) --> Zn+2(aq) + H2(g)
b) CaCO3(s) + 2H2O(l) --> Ca(OH)2(s) + H2CO3(aq)
c) CH4(g) + O2(g) --> CO2(g) + 2H2O(g)
d) Ag+(aq) + Cl-(aq) --> AgCl(s)
I said a) and c) were spontaneous, based on phase changes/delta-s. Does that seem correct?
I'm not quite sure how your rule works with phase changes/delta s.
a is spontaneous. (What if I had written Cu(s) + 2H^+(aq)==>Cu^+2 + H2(g). That is not spontaneous but it looks like the same reaction, doesn't it?
b is not because CaCO3 is largely insoluble.
c is spontaneous IF (and it's a big if) we get over the activitation energy (which is usually done with a match or an electric spark). Something to initiate the reaction. But it won't happen without the initial help.
d is spontaneous for AgCl is a solid, the reactants are in solution.
a works because Zn metal is above H^+ in the activity series.
c works because the products have less energy than the reactants but that is essentially true for all spontaneous reactions. I may not know what your definition of spontaneous reaction is.
e works because an insoluble ppt is formed.
To determine which reactions are spontaneous, we need to consider a few factors. One factor is the concept of Gibbs free energy (ΔG). A spontaneous reaction has a negative value of ΔG, indicating that it is thermodynamically favorable. Another factor is the activity series, which ranks elements based on their reactivity.
Let's analyze each reaction:
a) Zn(s) + 2H+(aq) → Zn+2(aq) + H2(g)
This reaction involves the displacement of hydrogen ions (H+) by zinc (Zn) metal. It is spontaneous because zinc is higher in the activity series compared to hydrogen. In other words, zinc is more reactive than hydrogen. Therefore, the reaction goes in the forward direction.
b) CaCO3(s) + 2H2O(l) → Ca(OH)2(s) + H2CO3(aq)
This reaction involves the dissolution of calcium carbonate (CaCO3) in water. However, CaCO3 is largely insoluble, meaning it doesn't easily dissolve in water. Therefore, this reaction is not spontaneous.
c) CH4(g) + O2(g) → CO2(g) + 2H2O(g)
This reaction is the combustion of methane (CH4) in oxygen (O2). Combustion reactions usually release energy and are spontaneous. However, it is important to note that this reaction requires an initial activation energy, typically provided by a match or spark. Once the reaction is initiated, it becomes spontaneous.
d) Ag+(aq) + Cl-(aq) → AgCl(s)
This reaction involves the combination of silver ions (Ag+) and chloride ions (Cl-) to form silver chloride (AgCl) precipitate. The formation of an insoluble precipitate typically indicates a spontaneous reaction. Therefore, this reaction is spontaneous.
In summary, based on the analysis above:
- Reaction a) is spontaneous because zinc is more reactive than hydrogen.
- Reaction b) is not spontaneous due to the low solubility of calcium carbonate.
- Reaction c) becomes spontaneous after an initial activation energy is supplied.
- Reaction d) is spontaneous because it forms an insoluble precipitate.