Final answer:
Changing the temperature of a system at equilibrium causes a shift in the position of equilibrium and a change in the equilibrium constant (Keq). In endothermic reactions, an increase in temperature increases Keq, while in exothermic reactions, it decreases Keq, in line with Le Chatelier's principle.
Step-by-step explanation:
Effect of Change in Temperature on Equilibrium
When considering how temperature affects a chemical equilibrium, it is important to understand that unlike changes in concentration or pressure, a change in temperature alters the value of the equilibrium constant (Keq). According to Le Chatelier's principle, if a system at equilibrium is subjected to a change in temperature, the system will adjust to minimize the effect of that change. In endothermic reactions, an increase in temperature shifts the equilibrium position to favor the formation of products, thus increasing Keq. Conversely, in exothermic reactions, increasing temperature shifts the equilibrium towards the reactants, decreasing Keq.
For example, in the synthesis of hydrogen iodide (HI) from hydrogen (H2) and iodine (I2), which is exothermic, an increase in temperature would shift the equilibrium to favor the formation of reactants—hydrogen and iodine—due to the system's attempt to absorb the added heat. This shift means that the equilibrium constant decreases. On the other hand, decreasing the temperature would shift the equilibrium towards products (HI), increasing Keq.
When a system at equilibrium is subjected to a change in temperature, the equilibrium position shifts in a way that tends to counteract the change. This is known as Le Chatelier's principle. If the temperature of the system is increased, the equilibrium will shift in the direction that absorbs heat. Similarly, if the temperature is decreased, the equilibrium will shift in the direction that releases heat.