A chemistry teacher uses two demonstrations to introduce the concept of equilibrium:…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A chemistry teacher uses two demonstrations to introduce the concept of equilibrium:
• Demonstration 1 – A uniform, 1.0m-long metal rod is perfectly balanced at its center on a knife-edge fulcrum. After minor oscillations damp out, the rod remains at rest.
• Demonstration 2 – A sealed reaction vessel at constant temperature contains a reddish-brown mixture of N2O4(g)⇌2NO2(g). After several minutes the intensity of the brown color ceases to change.
Students are asked to compare the two demonstrations in terms of the nature of the equilibrium established.
(a) For Demonstration 1, identify the type of equilibrium (dynamic or static) and provide one piece of evidence that supports your classification.
(b) For Demonstration 2, identify the type of equilibrium (dynamic or static) and provide one piece of evidence that supports your classification.
(c) Explain, with reference to particle motion and reaction rates, why the two demonstrations differ in the microscopic activity that persists *after* equilibrium is reached, even though both appear unchanged macroscopically.
(d) Suppose the temperature of the reaction vessel in Demonstration 2 is suddenly lowered by 15∘C and held constant at the new temperature. Predict qualitatively how the color intensity will change *while* the system re-establishes equilibrium, and explain your reasoning in terms of forward and reverse reaction rates.