Answer: decrease
Explanation: if ammonia (NH3) is added to the Zn half-cell, the following reactions may occur: 1. NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq) 2. Zn (s) ⇌ Zn2+ (aq) + 2e- When NH3 is added, it can react with water to form NH4+ and OH-. The OH- ions produced can react with Zn2+ ions from the Zn half-cell to form Zn(OH)2. The overall reaction can be represented as: Zn (s) + 2OH- (aq) + 2NH4+ (aq) ⇌ Zn(OH)2 + 2NH3 (aq) This reaction involves the consumption of Zn and OH- ions and the formation of Zn(OH)2 and NH3. Now, let's consider the effect on Ecell: 1. The addition of NH3 could shift the equilibrium of the reaction to the right, consuming Zn and OH- ions. 2. The decrease in Zn concentration could lead to a decrease in the rate of the Zn half-cell reaction. 3. As a result, the overall cell potential (Ecell) might decrease due to the slower rate of the Zn half-cell reaction. In conclusion, adding ammonia (NH3) to the Zn half-cell may cause Ecell to decrease due to the consumption of Zn and OH- ions, leading to a slower Zn half-cell reaction.