Equilibrium Conceptual

X_(g) + Y_(g) ↔ XY _(g)

In an experiment, X_(g) and Y_(g) were combined in a rigid container at constant temperature and allowed to react as shown in the equation above. The table provides the data collected during the experiment. Based on the data, which of the following claims is most likely correct?

• The reaction was about to reach equilibrium 15 minutes after the reactants were combined because the concentrations of X and XY were almost the same.

• The reaction reached equilibrium between 75 minutes and 155 minutes after the reactants were combined because the concentrations of X and XY remained constant.

• The reaction did not reach equilibrium because only 86% of the initial concentration of X was consumed.

• The reaction did not reach equilibrium because initially there was no XY inside the container.

Tags

NGSS.HS-PS1-5

X_(g) + Y_(g) ↔ XY_(g)

The particle diagram above illustrates the changes that take place when X_(g) and Y_(g) are placed inside a rigid container at constant temperature. Which of the following is a characteristic of a system at equilibrium that is best represented by the particle diagram?

• The particle diagram shows that initially the reaction proceeds to the right to form products, which is a characteristic of a system at equilibrium.

• The particle diagram shows that after 200 s the rate of the reverse reaction is slower than the rate of the forward reaction, which is a characteristic of a system at equilibrium.

• The particle diagram shows that after 200 s there are no observable changes in the amounts of reactants and products, which is a characteristic of a system at equilibrium.

• The particle diagram shows that between 0 s and 200 s the rates of the forward and reverse reactions are the same, which is a characteristic of a system at equilibrium.

CO(g) + 2 H₂(g) ⇄ CH₃OH(g) Δ H < 0

The synthesis of CH₃OH(g) from CO(g) and H₂(g) is represented by the equation above. The value of K_c for the reaction at 483 K is 14.5.

Which of the following explains the effect on the equilibrium constant, K_c, when the temperature of the reaction system is increased to 650 K?

• K_c will increase because the activation energy of the forward reaction increases more than that of the reverse reaction.

• K_c will increase because there are more reactant molecules than product molecules.

• K_c will decrease because the reaction is exothermic.

• K_c is constant and will not change.

Tags

NGSS.HS-PS1-5

The table above shows data for two reactions carried out in two separate evacuated 1.0-liter rigid containers at constant temperature of 298 K. To each container 0.50 mol of the appropriate reactants was added, and the reaction was allowed to reach equilibrium. Based on this information, which of the following correctly compares the relative concentrations of BrCl and NO present inside their respective containers at equilibrium?

• [BrCl]_eq = [NO]_eq because equimolecular mixtures of the reactants were allowed to reach equilibrium at the same constant temperature.

• [BrCl]_eq > [NO]_eq because Br₂ and Cl₂ are larger molecules that can collide more frequently to form products.

• [BrCl]_eq > [NO]_eq because the much larger K_eq for reaction 1 means that a much higher concentration of products will be present at equilibrium for reaction 1 compared with reaction 2.

• [BrCl]_eq < [NO]_eq because the much larger K_eq for reaction 1 means that hardly any products will be present at equilibrium compared with reaction 2.

Tags

NGSS.HS-PS1-5

NGSS.HS-PS1-7

At night, an equilibrium reaction between two different nitrogen compounds generates N₂O₅ in the atmosphere, as represented below.

Reaction 1: NO_3(g) + NO_2(g) ⇄ N₂O_5(g) K = 2.6×10⁻¹¹

A mixture of NO₃ and a ten-fold excess of NO₂ are placed inside a rigid container at constant temperature and allowed to reach equilibrium. Which of the following provides a correct comparison of the equilibrium concentrations of these chemical species, and why?

• [N₂O₅] << [NO₃] because a small K value indicates that the consumption of the reactants is favored at equilibrium.

• [NO₂] << [N₂O₅] because a small K value indicates that the consumption of the reactants is favored at equilibrium.

• [NO₂] << [NO₃] because a small K value indicates that the formation of the products is not favored at equilibrium.

• [N₂O₅] << [NO₂] because a small K value indicates that the formation of the products is not favored at equilibrium.

In the atmosphere, small water droplets are suspended in the air, forming an aerosol. N₂O_{5 (g)} can form HNO_{3 (aq)} under these conditions, as shown in reaction 2, represented below.

Reaction 1: NO_{3 (g)} + NO_{2 (g)} ↔ N₂O_{5 (g)}

Reaction 2: N₂O_{5 (g)} + H₂O _(l) → 2HNO_{3 (aq)}

Which of the following predicts the effect that the formation of will have on the equilibrium shown in reaction 1, and why?

• The equilibrium of reaction 1 will shift toward the formation of more product, because N₂O_{5 (g)} is removed when it reacts to form HNO_{3 (aq)}.

• The equilibrium of reaction 1 will shift toward the formation of more product, because H₂O _(l) acts as a catalyst for reaction 1.

• The equilibrium of reaction 1 will shift toward the formation of more reactants, because the product N₂O_{5 (g)} is removed when it reacts to form HNO_{3 (aq)}.

• The equilibrium of reaction 1 is not affected, because neither H₂O _(l) nor HNO_{3 (aq)} are gases.

Tags

NGSS.HS-PS1-6

Fe³⁺_(aq) + SCN^-_(aq) ↔ FeSCN²⁺_(aq)

When colorless solutions containing Fe³⁺_(aq) ions and SCN^-_(aq) ions are combined, a deep-red complex ion FeSCN²⁺_(aq), quickly forms, as shown in the net ionic equation above. Which of the following explains the observation that adding a few additional crystals of KSCN_(s) results in the red color of the solution becoming deeper?

• The added KSCN_(s) dissolves, disturbing the charge balance in the solution, causing Fe(SCN)_{3 (s)} to precipitate as a red solid.

• The added KSCN_(s) dissolves, causing the solution to become saturated in SCN^- ions, which appear red at high concentrations.

• The added KSCN_(s) dissolves, causing the reaction system to respond by producing more product to partially consume SCN^-_(aq) and reduce its concentration.

• The added KSCN_(s) dissolves, causing the reaction system to respond by forming more Fe³⁺ ions, which have a deep orange color at high concentrations.

Tags

NGSS.HS-PS1-5

Fe³⁺_(aq) + SCN^-_(aq) ⇄ Fe(SCN)²⁺_(aq)

For the reaction represented above, the value of the equilibrium constant, K_eq, is 240 at 25°C. From this information, correct deductions about the reaction at 25°C include which of the following?

I - The reaction is quite rapid.

II - The product is favored over the reactants at equilibrium.

III - The reaction is endothermic.

• I only

• II only

• I and II only

• II and III only

• I, II and III

For which of the equilibrium systems represented below will the amount of product(s) at equilibrium increase if the volume of the reaction vessel is increased at a constant temperature?

• PCl_5(g) ⇄ PCl_3(g) + Cl_2(g)

• 2 NO_(g) + O_2(g) ⇄ 2 NO_2(g)

• N_2(g) + O_2(g) ⇄ 2 NO_(g)

• 2 CO_(g) ⇄ C_(s) + CO_2(g)

Tags

NGSS.HS-PS1-6

For which of the following reaction mixtures at equilibrium would reducing the volume of the container at constant temperature cause the equilibrium to shift toward the products?

• SrCO_3(s) ⇄ SrO_(s) + CO_2(g)

• C_(s) + CO_2(g) ⇄ 2 CO_(g)

• CO_(g) + H₂O_(g) ⇄ CO_2(g) + H_2(g)

• 2 NO_2(g) ⇄ N₂O_4(g)