Question

4 hcl (g) + o₂ (g) ←→ 2 cl₂ (g) + 2 h₂o (g) equal numbers of moles of hcl and o₂ are placed in a closed system, and are allowed to reach equilibrium as represented by the equation above. which of the following must be true at equilibrium?

i. [hcl] must be less than [cl₂]. ii. [o₂] must be greater than [hcl]. iii. [cl₂] must equal [h₂o]. iv. [o₂] must be equal to [h₂o]
answer choices
a) i only b) ii only c) iii only
d) i and ii e) ii and iv f) ii and iii

Answer 1

At equilibrium, [HCl] must be less than [Cl₂] and [O₂] must be greater than [HCl]. Also, [Cl₂] must equal [H₂O]. The correct answer is option F) II and III.

Step-by-step explanation:

When equal numbers of moles of HCl (hydrochloric acid) and O₂ (oxygen) are placed in a closed system and allowed to reach equilibrium as represented by the equation 4 HCl (g) + O₂ (g) ↔ 2 Cl₂ (g) + 2 H₂O (g), the following statements can be evaluated:

1. [HCl] must be less than [Cl₂].
2. [O₂] must be greater than [HCl].
3. [Cl₂] must equal [H₂O].
4. [O₂] must be equal to [H₂O].

By looking at the stoichiometry of the balanced equilibrium equation, we can see that for every 4 moles of HCl that react, 1 mole of O₂ reacts, producing 2 moles of Cl₂ and 2 moles of H₂O. At equilibrium:

- As the reaction proceeds, HCl is consumed to produce Cl₂ and H₂O, so statement I is true: [HCl] must be less than [Cl₂].

- Since we started with equal moles of HCl and O₂ and the ratio of HCl to O₂ that reacts is 4:1, there will be some O₂ left unreacted indicating statement II is also true: [O₂] must be greater than [HCl].

- Statements III and IV are contingent upon the stoichiometry of the products and do not take into account the initial conditions. According to the balanced equation, the molar ratio of Cl₂ to H₂O is 1:1, so statement III is correct: [Cl₂] must equal [H₂O].

- Statement IV is false because there is no relationship stated in the balanced equation that dictates [O₂] must be equal to [H₂O].

Therefore, the correct answer is option F) II and III.