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Reaction Rates

Reaction Rates. Chapter 14 part I. Chemical Kinetics. Reactants –> Products. A reaction is defined by its reactants and products. Spontaneity refers to the inherent tendency for the process to occur. Spontaneous does not mean fast. ∆G = ∆H -T∆S. C diamond –> C graphite. Reaction Rates.

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Reaction Rates

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  1. Reaction Rates Chapter 14 part I

  2. Chemical Kinetics Reactants –> Products • A reaction is defined by its reactants and products. • Spontaneity refers to the inherent tendency for the process to occur. • Spontaneous does not mean fast. ∆G = ∆H -T∆S C diamond –> C graphite

  3. Reaction Rates • 2NO2(g)–> 2NO(g) + O2(g) • The above reaction is the decomposition of nitrogen dioxide a form of air pollution which contributes to acid rain. • Sidebar: acid anhydrides • Note the rate of change in concentration changes over time.

  4. The reaction rate is defined: Rate = (concentration of A at time t2-concentration of A at time t1) (t2-t1) aka: ∆ [A] /∆ t • Reaction Rate is the change in concentration of a reactant or product per unit time

  5. 2NO2(g)–> 2NO(g) + O2(g)

  6. 2NO2(g)–> 2NO(g) + O2(g)

  7. 2NO2(g)–> 2NO(g) + O2(g) • Calculate the average rate at which the concentration of NO2 changes over the first 50 seconds . • Note that NO2 decreases over time, so the ∆[NO2] is a negative quantity. So: • Rate = - ∆[NO2]/∆t

  8. Instantaneous Rate • Notice that over time the rate of reaction changes. • The rates in the tale to the left are average rates. • The value of the rate at a particular time is called the instantaneous rate.

  9. Instantaneous Rate cont. • To find the instantaneous rate one must find the tangent of the curve. • Slope of the tangent line = ∆ y/∆x (rise/run) • Rate = - ∆[NO2]/∆t • Or: Rate = -(slope of the tangent line)

  10. Reaction Rates • Rates of reactions may also be applied to products, not just reactants. • As NO2 is decomposed NO and O2 are produced, the rates are related but not necessarily the same. • The rates are different based on stoichiometry.

  11. Stoichiometry and Rates • Rate of consumption of NO2 = • Rate of production of NO = • 2 X’s the Rate of production of O2 Rate = - ∆[NO2]/∆t Rate = ∆[NO]/∆t Rate = 2(∆[O2]/∆t)

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