Can someone please help me?

Question

For the following problems, I had to refer to the reaction 2NH₃ (g) ↔ N₂ (g) + 3H₂ (g), and ΔH = 92.2 kJ.

1. What will be the effect on the concentration of H₂ if the temperature decreases?

A. H2 concentration will decrease.

B. H2 concentration will not change.

C. H2 concentration will increase, and pressure will decrease.

D. H2 concentration will not change, but ΔH will decrease.

E. H2 concentration will not change, but pressure will increase.

 

2. What will be the effect on the concentration of NH₃ if the pressure decreases?

A. NH3 concentration will decrease.

B. NH3 concentration will not change.

C. NH3 concentration will increase, and pressure will stay the same.

D. NH3 concentration will not change, but ΔH will decrease.

E. NH3 concentration will not change, but entropy will increase.

 

3. What will be the effect on N₂ if the concentration of NH₃ increases? _______

A. N2 concentration will decrease.

B. N2 concentration will not change.

C. N2 concentration will increase.

D. N2 concentration will not change, but ΔH will decrease.

E. N2 concentration will not change, but pressure will increase.

Answer 1

2NH₃ (g) ↔ N₂ (g) + 3H₂ (g), and ΔH = 92.2 kJ.

1. What will be the effect on the concentration of H₂ if the temperature decreases?

∆H is positive meaning heat is added (endothermic) so heat can be viewed as a reactant. According to Le Chatelier, decreasing temp (removing a reactant) will push the equilib to the reactant side, thus reducing the amount of H2. Option A is correct

 

2. What will be the effect on the concentration of NH₃ if the pressure decreases?

There are 4 mols of gas on the right (product) side and only 2 mols of gas on the left (reactant) side. So decreasing the pressure will cause the equilibrium to shift to the side with more mols and therefore concentration of NH3 will decrease. Option A is correct.

 

3. What will be the effect on N₂ if the concentration of NH₃ increases?

Since N2 is a product and NH3 a reactant, increasing NH3 will push the equilibrium to the product side and so N2 concentration will increase. Option C is correct.