基础化学-chapter_7_1.ppt

Example 7-2: Soil was found to be contaminated with radioactive Co-60, which has a half-life of 5.26 years (radioactive substances decay by first order processes and their rate of decay is normally reported by stating their half-lives.). The soil was collected for storage. How much years must pass before the radioactivity drops to 20% of its initial value? Assume the initial radioactivity of Co-60 is R, then: §3. Reaction Order and its Characteristics Solution: II. Second-order reaction 1/cA ? t: the slope is k (concentration-1 · time-1). §3. Reaction Order and its Characteristics §3. Reaction Order and its Characteristics §3. Reaction Order and its Characteristics §3. Reaction Order and its Characteristics Half-life (t1/2) of a second-order reaction: The half-life of a second-order reaction depends on initial concentration and becomes larger as time goes on. Example 7-3: Saponification of ethyl acetate at 298K is a second-order reaction: CH3COOC2H5 + NaOH CH3COONa + C2H5OH The initial concentrations of all reactants are 0.0100 mol · L-1, NaOH takes to use up 0.00566 mol · L-1 after 20 minutes of reaction. Calculate the rate constant k and half-life t1/2. §3. Reaction Order and its Characteristics Solution: III. Zero-order reaction cA ? t: the slope is -k (concentration · time-1). §3. Reaction Order and its Characteristics The half-life of a zero-order reaction depends on initial concentration and becomes smaller as time goes on. §3. Reaction Order and its Characteristics Relationships for zero-, first-, and second-order reactions Chapter 7 Rate of Reaction § 7-1. Reaction rate and its expressions § 7-2. Reaction mechanism and elementary reaction § 7-3. Reaction order and its characteristics § 7-4. Collision and transition-state theory § 7-5. Effect of temperature on reaction rate § 7-6. Effect of catalyst on reaction rate At the end of the session, you are expected to 1. define reaction rate and its expression; 2. distinguish between elementary rea