Question

Have cach group member explain to the group what happens if a system at equilibrium is subject to one of the following changes and why: a. the concentration of a reactant is increased b. a solid product is added c. the volume is decreased d. the temperature is ralsed

Short answer

a. Increasing reactant concentration shifts equilibrium towards products. b. Adding solid product has no effect on equilibrium. c. Decreasing volume shifts equilibrium to the side with fewer gas molecules. d. Raising temperature shifts equilibrium towards reactants for exothermic reactions and towards products for endothermic reactions.

Step-by-step solution

Explaining the Effect of Increased Reactant Concentration

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. Increasing the concentration of a reactant will shift the equilibrium position to the right, favoring the formation of products to reduce the concentration of the added reactant.

Explaining the Effect of Adding a Solid Product

Adding a solid product to a system at equilibrium does not change the equilibrium position if the solid is an inert substance. However, if the solid is a product of the reaction, adding it doesn't affect the equilibrium position for reactions with solid products as their concentrations are constants and do not appear in the expression for the equilibrium constant (K).

Explaining the Effect of Decreased Volume

Decreasing the volume of a gaseous system at equilibrium increases the pressure. According to Le Chatelier's principle, the system will adjust to minimize the pressure increase. This will shift the equilibrium in the direction that produces fewer gas molecules, which could either be towards the reactants or products, depending on which side of the reaction has fewer gas molecules.

Explaining the Effect of Raised Temperature

Raising the temperature of a system at equilibrium adds heat to the system. If the reaction is exothermic, the equilibrium will shift to absorb the added heat by favouring the reverse reaction (forming reactants). Conversely, if the reaction is endothermic, the equilibrium will shift to the right, favouring the formation of products.

Key concepts

Equilibrium Shift

Understanding how a system at equilibrium responds to external changes is crucial in chemistry. According to Le Chatelier's principle, a system at equilibrium will attempt to counteract any change applied to it. This behavior is referred to as an 'equilibrium shift.' When a stress, such as a change in concentration, pressure, or temperature, is applied to the system, the equilibrium moves in a direction that mitigates that stress. For instance, if additional reactant is introduced into the system, the equilibrium will shift toward the products to decrease the reactant concentration, working to re-establish equilibrium under the new conditions.

Visualizing a seesaw in balance can help illustrate this concept. If extra weight (the stress) is added to one side (the reactant side), the seesaw will tilt. The system then shifts to the other side (the product side) to regain balance. This adaptive behavior is pivotal in predicting the outcome of chemical reactions under various stresses.

Reactant Concentration Effect

When the concentration of a reactant is increased in a chemical reaction at equilibrium, the system responds by producing more products. As per Le Chatelier's principle, this happens because the system aims to reduce the concentration of the added reactant and restore equilibrium. An increased concentration of a reactant will cause a 'shift to the right,' or towards the product side of the equation.

Imagine adding more ingredients to a recipe than the recipe calls for. To balance it out and keep the taste consistent, you'd add more of the other ingredients, resulting in more final dish (the products) than you initially intended. Similarly, in a chemical reaction, the additional reactant 'forces' the reaction to proceed further to the product side, until the new balance is achieved.

Gaseous System Volume Change

A change in volume can significantly impact a gaseous system at equilibrium. If the volume of the container is decreased, this effectively increases the pressure inside the container, because the gas molecules are now in a smaller space. The equilibrium will shift in the direction that leads to fewer gas molecules, thus reducing the pressure and restoring a new equilibrium state. This shift could be toward the reactants or the products, depending on which side of the equation has a smaller number of moles of gas. This concept is an application of Le Chatelier's principle to changes in pressure due to volume changes in a gaseous system.

Impact of Volume Decrease:

Consider a room filled with people (molecules). If the room's size is suddenly reduced, it will become more crowded (increased pressure). To make it less crowded, some people would need to leave (a shift in equilibrium). The same principle applies to gas particles in a reduced volume.

Temperature Effect on Equilibrium

Temperature is a unique kind of stress on a chemical system as it affects the kinetic energy of the molecules involved in the reaction. A temperature increase adds energy to the system. For an exothermic reaction, which releases heat, this extra energy will shift the equilibrium toward the reactants, as the system tries to absorb the added heat and thus decreases its temperature. Conversely, for an endothermic reaction that absorbs heat, raising the temperature will shift the equilibrium toward the products to consume the excess heat.

Real-Life Analogy for Temperature Changes:

If you're cold and someone adds heat by turning up the thermostat, you'll stop shivering and feel comfortable (equilibrium shift to absorb heat). However, if you're too hot and someone cranks up the heat even more, you'll likely start seeking ways to cool down (like drinking cold water or moving to a cooler room), analogous to an equilibrium shift to release excess heat.