Reaction Rates

Objective: Explain the concepts and assumptions used in reaction rates.

Reaction rate describes change in concentration per time. A reactant’s disappearance rate is often reported as −Δ[A]/Δt so its magnitude is positive. Rate laws are determined from evidence and are not generally read from balanced coefficients. Temperature, concentration, exposed surface area, and catalysts can affect productive encounters or pathways. A catalyst lowers an activation barrier by providing another pathway, speeds approach to equilibrium, and does not change K at fixed temperature. The numerical exercises specify their rate laws explicitly.

Objective: Apply reaction rates to calculations, evidence, and specified situations.

For the application problems, define the system and list the quantities supplied before choosing a relation. Use reactant disappearance rate = −Δ[A]/Δt; rate=k[A]^n when experimentally specified. The relation must match the stated conditions. Convert to compatible units before substitution, preserve intermediate precision, and report the requested quantity with its unit or sign. When comparing alternatives, check the defining condition rather than a superficial word match. The worked examples below show the setup and calculation separately.