Chemical Equilibrium and Le Chatelier's Principle

Question 1

Which type of chemical reaction proceeds in only one direction, converting reactants completely into products that cannot easily reform the original reactants?

Accepted Answer

An irreversible reaction.

Question 2

What characterizes a reversible reaction?

Accepted Answer

It can proceed in both the forward and reverse directions under the same experimental conditions.

Question 3

What is the definition of chemical equilibrium in a reversible reaction?

Accepted Answer

It is a state where the rate of the forward reaction equals the rate of the reverse reaction, with no net change in concentrations.

Question 4

Why is chemical equilibrium described as a 'dynamic equilibrium'?

Accepted Answer

Reactants are continuously converted into products at the same rate that products are converted back into reactants.

Question 5

Which symbol is used to represent a reversible reaction in a chemical equation?

Accepted Answer

A double arrow (&#8652;).

Question 6

In the equation N2(g) + 3H2(g) &#8652; 2NH3(g), what does the symbol '(g)' represent?

Accepted Answer

Gas.

Question 7

Which of the following is a characteristic of a system at chemical equilibrium?

Accepted Answer

It must be a closed system.

Question 8

What is the effect of a catalyst on the position of chemical equilibrium?

Accepted Answer

A catalyst does not shift the position of equilibrium but helps the system reach equilibrium faster.

Question 9

Which principle states that if an external constraint is applied to a system in dynamic equilibrium, the system will adjust itself to counteract or minimize the effect of that constraint?

Accepted Answer

Le Chatelier's principle.

Question 10

For the general equilibrium system A + B &#8652; C + D, what happens if the concentration of reactant A is increased?

Accepted Answer

The system shifts to the right (forward direction) to consume the added reactant.

Question 11

For the general equilibrium system A + B &#8652; C + D, what happens if the concentration of product C is decreased (e.g., by removing it)?

Accepted Answer

The system shifts to the right (forward direction) to replace the lost product.

Question 12

For an exothermic reaction (Reactants &#8652; Products + Heat), what happens to the equilibrium position if the temperature is increased?

Accepted Answer

The system shifts to the left (reverse direction) to absorb the added heat.

Question 13

For an endothermic reaction (Reactants + Heat &#8652; Products), what happens to the equilibrium position if the temperature is decreased?

Accepted Answer

The system shifts to the left (reverse direction) to minimize the loss of heat.

Question 14

Consider the synthesis of ammonia: N2(g) + 3H2(g) &#8652; 2NH3(g). If the pressure on this system is increased, in which direction will the equilibrium shift?

Accepted Answer

To the right (forward direction) because it produces fewer moles of gas.

Question 15

For the reaction H2(g) + I2(g) &#8652; 2HI(g), what is the effect of increasing the pressure on the position of equilibrium?

Accepted Answer

There is no effect on the position of equilibrium.

Question 16

In the Haber Process for ammonia synthesis (N2(g) + 3H2(g) &#8652; 2NH3(g)), why is a high pressure (e.g., 200 atm) used?

Accepted Answer

To shift the equilibrium to the right, favoring the production of fewer moles of gas (ammonia).

Question 17

The Haber Process is exothermic (&Delta;H = -92.4 kJ/mol). Why is a compromise temperature of about 450 &deg;C used instead of a very low temperature to maximize ammonia yield?

Accepted Answer

At very low temperatures, the reaction rate becomes too slow to be commercially viable.

Question 18

What catalyst is used in the Contact Process for the manufacture of sulfur(VI) oxide (SO3)?

Accepted Answer

Vanadium(V) oxide (V2O5).

Question 19

In the practical demonstration of N2O4(g) &#8652; 2NO2(g) (&Delta;H = +57.2 kJ/mol), what color change is observed when the sealed tube is placed in a hot water bath?

Accepted Answer

The gas becomes much darker brown.

Question 20

Considering the equilibrium N2O4(g) &#8652; 2NO2(g) (&Delta;H = +57.2 kJ/mol), what color change is observed when the sealed tube is placed in an ice bath?

Accepted Answer

The gas becomes pale brown or nearly colorless.

Strong work.

Leave this flashcard session?