To determine which compound will cause a shift in the equilibrium of the chemical reaction given, we need to consider the common ion effect. The chemical reaction at equilibrium is:
[tex]\[ H_2SO_4(aq) \Leftrightarrow 2 H^+ (aq) + SO_4^{2-} (aq) \][/tex]
The common ion effect states that the addition of a compound that contains an ion already present in the reaction mixture will affect the position of the equilibrium.
Let's examine each of the given compounds to see if they contain any of the ions from the reaction ([tex]\( H^+ \)[/tex] and [tex]\( SO_4^{2-} \)[/tex]):
1. NaCl (Sodium Chloride):
- Dissociates into [tex]\( Na^+ \)[/tex] and [tex]\( Cl^- \)[/tex] in solution.
- Neither [tex]\( Na^+ \)[/tex] nor [tex]\( Cl^- \)[/tex] are present in the equilibrium reaction.
2. KNO_3 (Potassium Nitrate):
- Dissociates into [tex]\( K^+ \)[/tex] and [tex]\( NO_3^- \)[/tex] in solution.
- Neither [tex]\( K^+ \)[/tex] nor [tex]\( NO_3^- \)[/tex] are present in the equilibrium reaction.
3. MgSO_4 (Magnesium Sulfate):
- Dissociates into [tex]\( Mg^{2+} \)[/tex] and [tex]\( SO_4^{2-} \)[/tex] in solution.
- [tex]\( SO_4^{2-} \)[/tex] is present in the equilibrium reaction.
4. FeCl_3 (Iron(III) Chloride):
- Dissociates into [tex]\( Fe^{3+} \)[/tex] and [tex]\( Cl^- \)[/tex] in solution.
- Neither [tex]\( Fe^{3+} \)[/tex] nor [tex]\( Cl^- \)[/tex] are present in the equilibrium reaction.
Only [tex]\( MgSO_4 \)[/tex] contains the [tex]\( SO_4^{2-} \)[/tex] ion, which is a common ion in the given chemical equilibrium:
[tex]\[ H_2SO_4(aq) \Leftrightarrow 2 H^+ (aq) + SO_4^{2-} (aq) \][/tex]
Adding [tex]\( MgSO_4 \)[/tex] will increase the concentration of [tex]\( SO_4^{2-} \)[/tex] in the solution. According to Le Chatelier's principle, the system will respond to this change by shifting the equilibrium position to counteract the increase in [tex]\( SO_4^{2-} \)[/tex]. Therefore, it will shift the equilibrium to the left, reducing the concentration of [tex]\( SO_4^{2-} \)[/tex] by converting some of it back into [tex]\( H_2SO_4 \)[/tex].
Thus, the compound that will cause a shift in equilibrium because of the common ion effect is:
[tex]\[ \boxed{MgSO_4} \][/tex]
