Chemical Equilibrium Grade 12 Chemistry

Summary

This chemistry lesson introduces the concept of chemical equilibrium, focusing on how reactions can be reversible and not always go to completion. The instructor explains that equilibrium is reached when the forward and reverse reactions occur at the same rate, creating a dynamic balance. Key terms like 'closed system' and 'reversible reaction' are defined, and the conditions necessary for equilibrium are discussed. The lesson also touches on how equilibrium can be disturbed by factors like temperature, concentration, and pressure, setting the stage for further exploration in upcoming classes.

Takeaways

• 🔬 **Chemical Reaction Rates**: The lecture introduces the concept of reaction rates, explaining that reactions continue until one reactant is completely used, known as the limiting reagent.
• 🔄 **Reversible Reactions**: It's highlighted that not all reactions go to completion; many are reversible, meaning the products can be converted back into reactants.
• ⚖️ **Chemical Equilibrium**: The concept of chemical equilibrium is introduced, where the forward and reverse reactions occur at the same rate, resulting in a dynamic balance that never finishes.
• 🌡️ **Effect of Temperature**: The lecture suggests that temperature can influence the rate of evaporation and condensation, affecting the equilibrium state.
• 💧 **Water Evaporation Example**: An example of water in a sealed container is used to illustrate how evaporation and condensation can lead to a dynamic equilibrium.
• 📉 **Graphical Representation**: The lecture explains how to graph the rates of forward and reverse reactions, showing how they start high and low respectively, then equalize at equilibrium.
• 🔍 **Microscopic vs. Macroscopic Changes**: It's emphasized that at equilibrium, there are no observable changes macroscopically, but microscopically, the forward and reverse reactions continue at the same rate.
• 📋 **Requirements for Equilibrium**: A closed system is necessary for chemical equilibrium, where no mass can be transferred into or out of the system.
• 📈 **Concentration Changes Over Time**: The lecture describes how the concentration of reactants decreases and products increases over time, leveling off at equilibrium.
• 🔧 **Disturbing Equilibrium**: The script mentions that equilibrium can be disturbed by changing factors such as temperature, pressure, concentration, or by adding a catalyst.

Q & A

What is the main topic discussed in the script?

The main topic discussed in the script is chemical equilibrium, specifically focusing on the rates of reaction and how reversible reactions can lead to a state where the forward and reverse reactions occur at the same rate.

What is a limiting reagent and how does it affect a reaction?

A limiting reagent is a reactant that is completely consumed during a chemical reaction, thus determining the amount of product formed. When the limiting reagent is used up, the reaction stops, and the reaction is said to go to completion.

What is the difference between a reversible and an irreversible reaction?

A reversible reaction is one where the products can be converted back into reactants, and the reaction can proceed in both the forward and reverse directions. An irreversible reaction, on the other hand, goes to completion and does not have a reverse reaction under the same conditions.

What is meant by 'chemical equilibrium'?

Chemical equilibrium is a state in a reversible reaction where the rates of the forward and reverse reactions are equal, and there is no net change in the concentrations of the reactants and products over time.

Why is it important for a system to be closed to achieve chemical equilibrium?

A closed system is important for achieving chemical equilibrium because it prevents the loss or gain of mass, allowing the system to maintain the necessary conditions for the forward and reverse reactions to occur at the same rate.

How does the rate of the forward reaction change as a reaction progresses towards equilibrium?

As a reaction progresses towards equilibrium, the rate of the forward reaction decreases. This is because the concentration of reactants decreases as they are converted into products, leading to a slower rate of the forward reaction.

How does the rate of the reverse reaction change as a reaction progresses towards equilibrium?

The rate of the reverse reaction increases as a reaction progresses towards equilibrium. Initially, there may be little to no reverse reaction, but as products accumulate, the reverse reaction rate increases until it matches the rate of the forward reaction at equilibrium.

What is dynamic equilibrium and how is it different from a static equilibrium?

Dynamic equilibrium is a state where the forward and reverse reactions occur at the same rate, but the reactions are still happening, so there is a continuous process of conversion between reactants and products. Static equilibrium, on the other hand, would imply no reaction is occurring at all, which is not the case in a dynamic equilibrium.

What factors can disturb an existing chemical equilibrium?

Chemical equilibrium can be disturbed by changing the temperature, pressure, concentration of reactants or products, or by introducing a catalyst. These changes can cause the equilibrium to shift to re-establish a new balance according to Le Chatelier's principle.

What is Le Chatelier's principle and how does it relate to chemical equilibrium?

Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of the equilibrium will shift to counteract the change. This principle is used to predict the direction in which a chemical equilibrium will move in response to changes in temperature, pressure, or concentration.