Write the equilibrium expressions \(K_{c}\) for the following reactions. (a) \(\mathrm{CO}(\mathrm{g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{COCl}(\mathrm{g})+\mathrm{Cl}(\mathrm{g})\) (b) \(\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Br}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{HBr}(\mathrm{g})\) (c) \(2 \mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})+3 \mathrm{O}_{2}(\mathrm{~g})=2 \mathrm{SO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})\)

Imagine a dance floor where dancers are constantly pairing up and separating at the same rate; the population of dancing couples remains consistent over time. This is a visual way of understanding chemical equilibrium. When a chemical reaction reaches a state where the rate of the forward reaction equals the rate of the reverse reaction, the concentrations of reactants and products remain constant. It's important to clarify that this doesn't mean the reactions have stopped; they are still occuring, but their effects balance each other out.

At equilibrium, the system's properties, such as pressure, color, and concentration, won't show any net change despite the ongoing microscopic dance. This dynamic balance is crucial in chemical processes and product formation.

How close is a chemical system to reaching equilibrium? That's where the reaction quotient, denoted by Q, steps in. This nifty tool helps us forecast the direction in which a reaction will proceed to achieve equilibrium. The reaction quotient is calculated just like the equilibrium constant, using the same concentration expression, but with the current concentrations instead of those at equilibrium.

The comparison of Q to the equilibrium constant, K_c, can tell us whether a reaction needs to shift to produce more reactants or products. If Q is less than K_c, the reaction moves forward to produce more products. If Q is greater, it will shift to produce more reactants.

Ever wondered what happens when external conditions are altered on a system at equilibrium? Henri Louis Le Chatelier had the same question and deduced a principle about it. Le Chatelier's Principle states that when a system at chemical equilibrium experiences a change in concentration, temperature, volume, or pressure, it will adjust to counteract the imposed change and restore a new equilibrium.

For instance, adding more reactant to an equilibrium system causes it to produce additional products. Similarly, increasing the temperature for an exothermic reaction will cause the system to produce more reactants. Understanding this concept allows chemists to optimize conditions for desired product yields in industrial reactions.

If chemical reactions were recipes, stoichiometry would be the section about the amount of each ingredient. Stoichiometry involves the quantitative relationship between reactants and products in a chemical reaction. It's all about the mole ratios derived from a balanced chemical equation, which tell us how much of each substance is needed or produced.

In essence, stoichiometry provides the mathematical framework behind reactions, ensuring that atoms are conserved and allowing us to predict the amounts of products formed. This is essential in various fields, from designing chemical reactors to determining the fuel efficiency of vehicles.