chem sf 7 - Factors Affecting Reaction Rate Nature of the...

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Tro, Chemistry: A Molecular Approach 1 Factors Affecting Reaction Rate Nature of the Reactants nature of the reactants means what kind of reactant molecules and what physical condition they are in. small molecules tend to react faster than large molecules; gases tend to react faster than liquids which react faster than solids; powdered solids are more reactive than “blocks” more surface area for contact with other reactants certain types of chemicals are more reactive than others e.g., the activity series of metals ions react faster than molecules no bonds need to be broken
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Tro, Chemistry: A Molecular Approach 2 increasing temperature increases reaction rate chemist’s rule of thumb - for each 10° C rise in temperature, the speed of the reaction doubles for many reactions there is a mathematical relationship between the absolute temperature and the speed of a reaction discovered by Svante Arrhenius which will be examined later Factors Affecting Reaction Rate Temperature
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Tro, Chemistry: A Molecular Approach 3 catalysts are substances which affect the speed of a reaction without being consumed. most catalysts are used to speed up a reaction, these are called positive catalysts catalysts used to slow a reaction are called negative catalysts. homogeneous = present in same phase heterogeneous = present in different phase how catalysts work will be examined later Factors Affecting Reaction Rate Catalysts
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Tro, Chemistry: A Molecular Approach 4 generally, the larger the concentration of reactant molecules, the faster the reaction i ncreases the frequency of reactant molecule contact concentration of gases depends on the partial pressure of the gas higher pressure = higher concentration concentration of solutions depends on the solute to solution ratio (molarity) Factors Affecting Reaction Rate Reactant Concentration
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Tro, Chemistry: A Molecular Approach 5 The Effect of Temperature on Rate changing the temperature changes the rate constant of the rate law Svante Arrhenius investigated this relationship and showed that: = - RT E a e A k R is the gas constant in energy units, 8.314 J/(mol K) where T is the temperature in kelvins A is a factor called the frequency factor E a is the activation energy , the extra energy needed to start the molecules reacting
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Tro, Chemistry: A Molecular Approach 6 Activation Energy and the Activated Complex energy barrier to the reaction amount of energy needed to convert reactants into the activated complex aka transition state the activated complex is a chemical species with partially broken and partially formed bonds always very high in energy because partial bonds
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Tro, Chemistry: A Molecular Approach 7 The Arrhenius Equation: The Exponential Factor the exponential factor in the Arrhenius equation is a number between 0 and 1 it represents the fraction of reactant molecules with
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chem sf 7 - Factors Affecting Reaction Rate Nature of the...

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