Lesson Chemical Kinetics
Reaction Rate
- For the reaction “A B” there are two ways of measuring rate:
(1) the speed at which the reactants disappear
(2) the speed at which the products appear
- Reactions are reversible, so as products accumulate they can begin to turn back into reactants.
- Early on the rate will depend on only the amount of reactants present.
- We want to measure the reactants as soon as they are mixed.
- The most useful (and general) way of measuring the rate of the reaction is in terms of change in concentration per unit time…
Rate = ∆[A]/∆t limits to Δ[A]/Δt
Most Common Units… Rate = M/s
(Remember…Molarity (M) = moles/Liter)
Factors that Affect Reaction Rate Constant
1. Temperature: At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy
- Collision Theory: When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place.
- Kinetic Theory: Increasing temperature means the molecules move faster.
2. Concentrations of reactants
- As the concentration of reactants increases, so does the likelihood that reactant molecules will collide.
3. Catalysts
- Speed up reactions by lowering activation energy
4. Surface area of a solid reactant
- Bread and Butter theory: more area for reactants to be in contact
5. Pressure of gaseous reactants or products
- Increased number of collisions
160 trang
04/04/2025
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File đính kèm:
- lesson_chemical_kinetics.ppt
Nội dung text: Lesson Chemical Kinetics
- CHEMICAL KINETICS
- What are Chemical Kinetics?
- Chemical Kinetics •Kinetics: the study of how fast chemical reactions occur. (in contrast to Thermodynamics: which determines if a reaction take place) Our goal: is to understand chemical reactions at the molecular level. Speed of a reaction: is measured by the change in concentration with time. Important factors which affect rates of reactions: – reactant concentration – temperature – action of catalysts – surface area – pressure of gaseous reactants or products
- Kinetics • Studies the rate at which a chemical process occurs. • Besides information about the speed at which reactions occur, kinetics also sheds light on the reaction mechanism (exactly how the reaction occurs).
- Outline: Kinetics Reaction Rates How we measure rates. How the rate depends on amounts Rate Laws of reactants. How to calculate amount left or Integrated Rate Laws time to reach a given amount. How long it takes to react 50% of Half-life reactants. How rate constant changes with Arrhenius Equation temperature. Link between rate and molecular Mechanisms scale processes.
- Reaction Rates
- Reaction Rates Rates of reactions can be determined by monitoring the change in concentration of either reactants or products as a function of time t. [A] = concentration of reactant A
- Reaction Rate • For the reaction “A → B” there are two ways of measuring rate: (1)the speed at which the reactants disappear (2) the speed at which the products appear • Reactions are reversible, so as products accumulate they can begin to turn back into reactants.
- Reaction Rate • Early on the rate will depend on only the amount of reactants present. • We want to measure the reactants as soon as they are mixed. • The most useful (and general) way of measuring the rate of the reaction is in terms of change in concentration per unit time Rate = ∆[A]/∆t limits to Δ[A]/Δt Most Common Units Rate = M/s (Remember Molarity (M) = moles/Liter)
- Chemical Kinetics Thermodynamics – does a reaction take place? Kinetics – how fast does a reaction proceed? Reaction rate is the change in the concentration of a reactant or a product with time (M/s). A B [A] rate = - [A] = change in concentration of A over t time period t [ B] [B] = change in concentration of B over rate = t time period t Because [A] decreases with time, [A] is negative.
