Question

On which of the following the relative amounts of reactants and products at equilibrium do not depend? (1) The nature of the substances involved. (2) The state of the system. (3) The temperature. (4) The direction from which the equilibrium is approached.

Short answer

The direction from which the equilibrium is approached.

Step-by-step solution

Understand Chemical Equilibrium

Chemical equilibrium is a state in which the relative concentrations of reactants and products remain constant over time. The rates of the forward and reverse reactions are equal at this point.

Factors Affecting Equilibrium

Identify factors that affect the position of equilibrium. These include the nature of the substances involved, the temperature, the pressure (for gases), and the presence of catalysts.

Analyze Each Option

Analyze each given option to determine which one does not affect the relative amounts of reactants and products at equilibrium.

Option 1: The Nature of Substances Involved

The nature and properties of the reactants and products (such as their chemical identities and bond energies) directly affect the equilibrium position.

Option 2: The State of the System

The physical state (solid, liquid, gas) and the phase of the substances involved affect equilibrium. Hence, the state of the system matters in determining the equilibrium positions.

Option 3: The Temperature

Equilibrium constants are temperature-dependent. Changing the temperature will affect the relative amounts of reactants and products at equilibrium.

Option 4: The Direction of Approach

The direction from which equilibrium is approached does not affect the relative amounts of reactants and products at equilibrium. Regardless of starting with mostly reactants or products, the system will reach the same equilibrium states.

Conclusion

Based on the analysis, option 4 (the direction from which the equilibrium is approached) is the correct choice, as it does not affect the equilibrium position.

Key concepts

Factors Affecting Equilibrium

Chemical equilibrium is influenced by several key factors.
Understanding these will help explain why the relative amounts of reactants and products change or remain stable.

First, the nature of the substances involved is crucial. Different chemicals have varying properties and bond energies, which affect the equilibrium position.
The physical state (solid, liquid, or gas) plays a role too, as it can influence reaction dynamics.
Temperature is another significant factor. It determines the equilibrium constant and can shift the position of equilibrium.
Pressure impacts equilibrium for reactions involving gases, as changing pressure changes system volume.
Lastly, catalysts speed up reactions but do not alter equilibrium positions.
These factors collectively ensure that the system can reach equilibrium and maintain the concentration balance of reactants and products.

Equilibrium Constants

The equilibrium constant (K) is fundamental to understanding chemical equilibrium.
It expresses the ratio of product concentrations to reactant concentrations at equilibrium.

Mathematically, it is written as:
\( K = \frac{[products]}{[reactants]} \)
Where the concentrations are those at equilibrium.
If the K value is high, it means the products are favored at equilibrium.
Conversely, a low K value indicates that the reactants are more prevalent.

However, K is not constant under all conditions; only the temperature affects it.
Changes in temperature can shift the equilibrium position and thus change the K value.
For exothermic reactions, increasing temperature decreases K, favoring reactants.
For endothermic reactions, increasing temperature increases K, favoring products.
Understanding this helps predict how a system might react to changes in conditions.

Forward and Reverse Reactions

In a chemical equilibrium, both the forward and reverse reactions occur simultaneously.
At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction.
This dynamic balance is crucial to maintaining equilibrium concentrations of reactants and products.

The forward reaction converts reactants to products, and the reverse reaction converts products back to reactants.
\[ \text{A} + \text{B} \rightleftharpoons \text{C} + \text{D} \]
If the system is disturbed, such as by changing temperature, pressure, or concentrations, it will shift to counteract the disturbance, known as Le Chatelier's Principle.
Reactants or products can be added or removed to see temporary changes. However, the system will adjust to restore equilibrium.
Regardless of how the equilibrium is approached, the final position of equilibrium remains the same, ensuring the relative concentrations of reactants and products are constant over time.