Chemical Kinetics - Initial Rates Method

The Organic Chemistry Tutor24 minutes read

Chemical kinetics studies reaction rates while thermodynamics focuses on spontaneity. Reactant concentration decreases, while product concentration increases, with rates determined by the order of each reactant.

Insights

  • Chemical kinetics focuses on reaction speed and how it changes over time, contrasting with thermodynamics' emphasis on spontaneity and energy changes in reactions.
  • The rate of a chemical reaction is determined by the order of each reactant, with different orders leading to exponential changes in reaction rates based on concentration adjustments, highlighting the significant impact of reactant order on reaction speed.

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Recent questions

  • What does chemical kinetics study?

    Reaction rates and speed of reactions.

  • How is reaction rate measured?

    By the change in concentration over time.

  • What factors influence reaction speed?

    Reactant concentrations, temperature, and catalysts.

  • How is the rate law expression determined?

    By comparing rate changes with concentration changes.

  • What is the difference between chemical kinetics and thermodynamics?

    Chemical kinetics studies reaction rates, while thermodynamics focuses on spontaneity.

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Summary

00:00

Chemical kinetics vs. thermodynamics: reaction speed explained

  • Chemical kinetics studies reaction rates and how fast reactions occur, distinct from thermodynamics which focuses on spontaneity.
  • Thermodynamics determines if a reaction is energetically favorable, like diamond converting to graphite, which is spontaneous but slow.
  • Combustion of glucose with oxygen is another spontaneous yet slow reaction due to high activation energy.
  • Chemical kinetics describes reaction speed, contrasting with thermodynamics' focus on spontaneity.
  • As reactions progress, reactant concentration decreases while product concentration increases.
  • Rate of a reaction is measured by the change in concentration of products or reactants over time.
  • Rate of reaction with respect to a reactant is negative, while with respect to a product, it's positive.
  • Average rate of appearance or disappearance of a substance is calculated by the change in concentration over time.
  • Rate of a chemical reaction is proportional to the coefficients of substances in the reaction.
  • Calculations for average rates of disappearance and appearance involve molar ratios and time differences.

19:46

Reaction Rate Determined by Reactant Order

  • The rate of the reaction is determined by the order of each reactant: first order for a, second order for b, third order for c, and zero order for d.
  • The overall order of the reaction is found by summing the exponents of each reactant, resulting in a sixth-order overall reaction.
  • Doubling the concentration of a will double the rate of the reaction, as it is first order with respect to a.
  • Increasing the concentration of b by a factor of 2 will increase the rate by a factor of 4, as it is second order with respect to b.
  • Tripling the concentration of c will increase the rate by a factor of 27, as it is third order with respect to c.
  • Increasing the concentration of d will not affect the rate, as it is zero order with respect to d.
  • The reactant with the highest order, in this case c, has the greatest effect on the rate of the reaction.
  • To determine the rate law expression, the orders of each reactant are found by comparing rate changes with concentration changes in experimental trials.
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