Kinetics & Equilibrium Vocabulary

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Activated complex

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The temporary, intermediate product in a chemical reaction.

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Activation energy

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*The amount of energy needed to form an activated complex from reactants

*The amount of energy needed to start a reaction

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catalyst

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*A substance that alters the speed of a chemical reaction without being permanently changed

*Provides an alternate reaction pathway that requires a lower activation energy

*Only changes the potential energy of the activated complex, not the reactants or products

*The shortcut from A to B

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endothermic

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*A process that absorbs heat, producing products with more potential energy than the reactants in a chemical reaction

*In a potential energy diagram, the products are higher up than the reactants

*ΔH is positive

*Will decrease the temperature of the surroundings

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Enthalpy

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*The heat energy absorbed or released by a system (ΔH)

*Systems in nature tend to change towards lower enthalpy (and higher energy)

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entropy

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*A measure of the disorder or randomness of a system

*systems in nature tend to change towards higher entropy (and lower energy)

*the more possibilities for different arrangements of particles, the more entropy there is

*increases  from solid to liquid to gas

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equilibrium

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*A condition in which the rates of opposing reactions are equal

*the concentration of reactants and products will remain constant, but not necessarily equal

*always dynamic in chemistry, meaning both opposing reactions are continuously occurring

*two types for physical changes: phase and solution

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exothermic

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*A process that releases heat, producing products with less potential energy than the reactants in a chemical reaction 

*ΔH is negative

*In a potential energy diagram, the products will be lower than the reactants

*Will increase the temperature of the surroundings

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Heat of reaction

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*The amount of heat absorbed or released during a chemical reaction

*Symbolized as ΔH, is - when exothermic, + when endothermic (see Table I for values)

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LeChatelier’s Principle

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*A system at equilibrium will react to reduce a stress

*If you add concentration or temperature, the system will shift away (to the other side of the equation)

*If you remove/take away concentration or temperature, the system will stay on the same side of the equation

*Pressure only affects gases: if the pressure is increased the system will shift to the side with fewer moles of gas; if the pressure is deceases the system will shift to the side with more moles of gas

*a catalyst will not cause a shift in a system, but will increase the speed of both reactions equally