Question

$$ 2 \mathrm{KClO}_{3}(s) \rightleftharpoons 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g) $$ Predict the effect (shift right, shift left, or no effect) of these changes. (a) adding \(\mathrm{KCl}\) to the reaction mixture (b) adding \(\mathrm{KClO}_{3}\) to the reaction mixture (c) adding \(\mathrm{O}_{2}\) to the reaction mixture (d) removing \(\mathrm{O}_{2}\) from the reaction mixture

Short answer

The effect on the equilibrium will be: (a) shift left, (b) shift right, (c) shift left, (d) shift right.

Step-by-step solution

Understanding Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. This principle can be used to predict the effects of adding or removing substances from a reaction mixture.

Predicting the Effect of Adding KCl

Adding KCl to the reaction mixture increases the concentration of one of the products. According to Le Chatelier's Principle, the system will react by favoring the reverse reaction to decrease the concentration of KCl. Therefore, the equilibrium will shift left.

Predicting the Effect of Adding KClO3

Adding KClO3 to the reaction mixture increases the concentration of the reactant. This will cause the equilibrium to shift to the right as the system tries to use the added reactant to form more products.

Predicting the Effect of Adding O2

The addition of O2 increases the concentration of one of the products. Le Chatelier's Principle predicts that the equilibrium will shift to the left, favoring the formation of reactants to reduce the concentration of O2.

Predicting the Effect of Removing O2

Removing O2 from the reaction mixture decreases the concentration of a product. The system will try to replace the lost O2 by shifting the equilibrium to the right. This will favor the production of more O2 from the decomposition of KClO3.

Key concepts

Chemical Equilibrium

Let's unpack the concept of chemical equilibrium with an easy-to-grasp analogy. Imagine a dance hall where dancers (representing reactants) continuously pair up to form couples (products) and at the same time, some couples break up to join the dance floor again. When the rate of pairing up equals the rate of breaking up, the number of couples and dancers remains constant. That's chemical equilibrium in a chemical reaction—when the rate of the forward reaction equals the rate of the reverse reaction, keeping the concentrations of reactants and products constant over time.

However, it's important to note that 'constant' doesn't mean the reactants and products are in equal amounts; it simply refers to a steady state where their amounts do not change anymore. Additionally, achieving equilibrium does not mean that the reactions stop occurring; they still proceed in both directions, but at identical rates.

Reaction Quotient

To better understand adjustments in a chemical system, let’s dive into the concept of the reaction quotient, denoted as Q. Picture it like a snapshot of a running race where the position of the runners (reactants and products) tells you how far the race (reaction) has progressed. It’s a ratio of the concentrations of products over reactants, raised to the power of their coefficients at any point in time before equilibrium is reached.

The reaction quotient is pivotal in determining the direction of the shift to reach equilibrium. If Q is less than the equilibrium constant (K), the race isn't over, and the forward reaction will speed up to create more products. Conversely, if Q is greater, the runners have overshot and the reaction needs to reverse a bit to hit the equilibrium 'finish line'. This comparison helps us predict whether the reaction will shift right (toward products) or left (toward reactants) to reach that equilibrium.

Equilibrium Shift

Le Chatelier’s principle is like a balancing scale. When you add weight (change in conditions) to one side, the scale tips — and this scale loves balance. It immediately adjusts the weights to regain equilibrium. In the context of our given chemical reaction, imagine adding more reactants or products as that 'extra weight'. The reaction adjust by shifting to oppose the change: if we add more product (weighing the scale down on the product side), it shifts left to reduce it; if we add more reactant, it shifts right to use it up.

Factors that cause a shift include change in concentration, pressure, or temperature. Removing a substance or reducing its concentration also prompts a shift towards its side to replace it. It’s important for students to remember that equilibrium is dynamic; it will always find a way to readjust and maintain a balance following a disturbance.

Reactants and Products

Reactants and products are the starting line and finish line of the chemical race, respectively. Reactants are the substances you begin with, which undergo chemical changes during the reaction. Products, on the other hand, are what you end up with; they are formed as a result of the reaction. Considering our reaction example where you add or remove one of these key players, the race course changes, and the reaction adjusts its direction accordingly.

In a classroom scenario, using actual physical props to represent reactants and products can greatly aid in students’ comprehension. Reminding them to visualize these not merely as static entities but as active participants in a dynamic process reinforces their understanding of how and why chemical reactions progress and reach equilibrium.