The normal freezing point of ammonia is -78 degrees celsius. Predict the signs of Delta H, Delta S, and Delta G for ammonia when it freezes at -80 degrees celsius and 1 atm: NH3 (l) —> NH3 (s)
The correct answer and explanation is:
Answer:
For the freezing of ammonia at −80∘C-80^\circ C and 1 atm: NH3(l)→NH3(s)NH_3 (l) \rightarrow NH_3 (s)
- ΔH (Enthalpy Change): Negative (-)
- ΔS (Entropy Change): Negative (-)
- ΔG (Gibbs Free Energy Change): Negative (-)
Explanation:
- ΔH (Enthalpy Change, Heat Released or Absorbed)
- Freezing is an exothermic process, meaning heat is released as the liquid transitions to a solid. The molecules slow down and lose kinetic energy.
- Since energy is leaving the system, ΔH is negative.
- ΔS (Entropy Change, Disorder of the System)
- Entropy (SS) represents the level of disorder or randomness in a system.
- A liquid has more disorder (higher entropy) compared to a solid because molecules in the liquid state can move more freely.
- When ammonia freezes, the molecules become more ordered in the solid phase.
- Since the system becomes more ordered, ΔS is negative.
- ΔG (Gibbs Free Energy Change, Spontaneity of the Process)
- The Gibbs free energy equation is: ΔG=ΔH−TΔS\Delta G = \Delta H – T\Delta S
- At the normal freezing point (−78∘C-78^\circ C), ΔG is zero because the system is at equilibrium.
- Here, ammonia is freezing at −80∘C-80^\circ C, which is below its normal freezing point. This means the surroundings are colder, favoring the freezing process.
- Since freezing is spontaneous under these conditions, ΔG is negative.
Conclusion:
Since the temperature is below the normal freezing point, ammonia will freeze spontaneously. The process releases heat (negative ΔH), decreases entropy (negative ΔS), and is thermodynamically favored (negative ΔG).
Now, I’ll generate an image illustrating this freezing process.
Here is the generated scientific illustration showing the phase transition of ammonia (NH₃) from liquid to solid at -80°C. It depicts the molecules becoming more structured as ammonia freezes, releasing heat in the process. Let me know if you need any modifications!
