chem lecture ch13
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| Reaction rate | The rate of a reaction is determined by measuring the amount of product or products formed or of reactants consumed per unit time.Reaction rates are generally not constant throughout the reaction. They commonly change as the reactants are used up.
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| 5 factors that effect reaction rate | 1. Chemical nature of the reactants
2. Ability of the reactant to meet
3. Concentration of the reactants
4. Temperature
5. Presence of a catalyst
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| Catalysts | Catalysts are substances, that increase the rates of chemical reaction without being used up.
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| Rate laws | Rate laws give reaction rates as the function of concentrations of reaction partners.
A + B --> Products. The rate law can not be predicted from the overall balanced reaction equation. Rate = k * [ A ]m * [ B ]n
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| rate constant k | value depends on the particular reaction studied as well as the temperature at which the reaction is studied. The constant k is temperature dependent.
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| rate law for EX: H2SeO3 + 6 I- + 4 H+ ---> Se + 2 I3- + 3 H2O | Rate = k [H2SeO3 ] [ I- ]3 [ H+ ]2
The overall reaction rate here is 6.
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| Integrated rate laws | give concentrations as a function of time. To relate concentrations to time, we look at the concentrations at times 0 [s] and t [s]. Then we have two concentrations, namely [ A ]0 and [ A ]t.
rate law can be transformed into: [ A ]t = [ A ]0 e-kt
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| Half-life (1st order reaction) | The half-life of a reactant is a measure of its speed of reaction. It is the amount of time required for half of the reactant to disappear.
For a 1. order reaction we find [ A ]t = ½ [ A ]0 ; t1/2= ln2/K. 1. For any particular 1. order reaction, t½ is co
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| 2nd Order reaction | A 2. order reaction can have a rate law like: Rate = k [ B ]^2
The relationship between concentrations and time is given by: 1/[B]t-1/[B]0=kt
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| Half-life (2nd order reaction) | The half-life of a reactant is a measure of its speed of reaction. It is the amount of time required for half of the reactant to disappear.
The half-life of a 2. order reaction does depend on the initial reactant concentrations.
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| Reaction rates are related to the number of effective collisions between reactant particles. An effective collision is one that gives products. Only a small fraction of collisions gives rise to products. Why? | A factor that can increase the number of effective collisions is concentration.
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| activation energy | The minimum energy needed for a successful collision.
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