Question

Suppose the reaction system $$2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{SO}_{3}(g)$$ has already reached equilibrium. Predict the effect of each of the following changes on the position of the equilibrium. Tell whether the equilibrium will shift to the right, will shift to the left, or will not be affected. a. Additional \(\mathrm{SO}_{2}(g)\) is added to the system. b. The \(\mathrm{SO}_{3}(g)\) present is liquefied and removed from the system. c. A very efficient catalyst is used.

Short answer

a. The equilibrium will shift to the right. b. The equilibrium will shift to the right. c. The equilibrium will not be affected.

Step-by-step solution

a. Additional SO₂(g) is added to the system.

According to Le Chatelier's principle, if the concentration of a reactant (in this case, SO₂) is increased, the system will adjust itself by shifting the equilibrium in the direction that consumes the reactant. In this case, that is the forward reaction (to the right), where SO₂ reacts with O₂ to produce SO₃. Therefore, the equilibrium will shift to the right.

b. The SO₃(g) present is liquefied and removed from the system.

According to Le Chatelier's principle, if the concentration of a product (in this case, SO₃) is decreased, the system will adjust itself by shifting the equilibrium in the direction that produces more of the product. In this case, that is the forward reaction (to the right), where SO₂ reacts with O₂ to produce SO₃. Therefore, the equilibrium will shift to the right.

c. A very efficient catalyst is used.

Catalysts work by lowering the activation energy of a reaction, which increases the reaction rate. However, catalysts affect both the forward and reverse reactions equally, meaning that the relative rates of the two reactions do not change. As a result, using a catalyst does not affect the position of the equilibrium. In this case, the equilibrium will not be affected.

Key concepts

Le Chatelier's Principle

When a system at chemical equilibrium is disturbed by changing the conditions, Le Chatelier's principle helps predict how the equilibrium will shift to counteract the disturbance. This principle is a crucial concept in chemistry. It's all about how systems adjust to minimize change.

Le Chatelier's principle can be thought of as the system's response to regain balance. Here's how it works in different scenarios:

• If you add more of a reactant or a product, the system will shift to decrease that substance.
• If you remove a reactant or a product, the system will move to increase the concentration of the missing component.
• Changing pressure or temperature also changes the equilibrium, but these effects depend on the specifics of the reaction and the gases involved.

For example, in our exercise, when \[ ext{SO}_{2} ext{(g)}\] is added, the system shifts to the right to form more \[ ext{SO}_{3} ext{(g)}\], trying to use up the additional \[ ext{SO}_{2} ext{(g)}\]. Similarly, removing some \[ ext{SO}_{3} ext{(g)}\] results in the equilibrium shifting to the right to produce more \[ ext{SO}_{3} ext{(g)}\] to make up for the loss.

Reaction Rates

The speed at which a chemical reaction proceeds is called the reaction rate. Imagine reaction rates as the race towards forming products from reactants. Faster reactions mean products are made quickly, while slower reactions take their time.

Reaction rates can be influenced by several factors:

• Concentration of Reactants: Increasing the concentration usually increases the reaction rate as more reactant particles are available to collide.
• Temperature: Higher temperatures typically increase reaction rates as particles move faster and collide more frequently and energetically.
• Surface Area: Greater surface area allows more contact between reactant molecules, speeding up reaction rates.

Catalysts also play a role and are discussed in the next section. However, it's important to note that while reaction rates speed up, it doesn't mean that the equilibrium position changes—it just reaches equilibrium faster.

Catalysts

Imagine catalysts as magical helpers that make chemical reactions happen more quickly without being changed themselves. They lower the activation energy required to start a reaction, which means reactions can proceed more smoothly and quickly.

Key characteristics of catalysts include:

• They do not alter the equilibrium position, as they accelerate both forward and reverse reactions equally.
• Catalysts are not consumed in the reaction, so they can be used repeatedly.
• Even though they speed up the approach to equilibrium, they do not change the amounts of reactants or products at equilibrium.

In our reaction example, introducing a catalyst would make the \[ ext{SO}_{2} ext{(g)} + ext{O}_{2} ext{(g)} ightleftharpoons ext{SO}_{3} ext{(g)}\] equilibrium reached faster, but it wouldn't shift the balance between products and reactants.