Equilibrium Systems 15.1a: Closed Systems & Reaction Equilibrium

Closed System in order for equilibrium to be studied there must be a boundary between the system and the surroundings in order for equilibrium to be studied there must be a boundary between the system and the surroundings gaseous systems must be closed systems where no matter can enter or exit gaseous systems must be closed systems where no matter can enter or exit collision-reaction theory is used to explain chemical systems, both fast and slow collision-reaction theory is used to explain chemical systems, both fast and slow not all rxtn’s are quantitative, forward and reverse rxtn’s can occur simultaneously in a closed system not all rxtn’s are quantitative, forward and reverse rxtn’s can occur simultaneously in a closed system

Closed system con’t Forward Reaction Forward Reaction arrow points from left to right arrow points from left to right ----> ----> reactants form products reactants form products Reverse Reaction arrow points from right to left <---- products form reactants When both arrows are shown it is considered an equilibrium equation > <

Equilibrium two opposing changes occur at equal rates two opposing changes occur at equal rates dynamic – not static dynamic – not static

Equilibrium dynamic equilibrium dynamic equilibrium may seem like no changes are occurring but there are changes may seem like no changes are occurring but there are changes no NET changes no NET changes When did this reaction reach it? When did this reaction reach it?

at equilibrium, forward and reverse reaction rates are equal at equilibrium, forward and reverse reaction rates are equal

Chemical Equilibrium The state of a chemical reaction in which its forward and reverse reactions occur at equal rates so that the concentration of the reactants and products does not change with time.

Reaction Equilibrium position of an equilibrium can be determined using % yield position of an equilibrium can be determined using % yield yield of product compared to maximum possible yield at equilibrium (actual/theoretical) yield of product compared to maximum possible yield at equilibrium (actual/theoretical) four categories of reactions at equilibrium four categories of reactions at equilibrium % equilibrium % equilibrium Negligiblenon-spontaneous Negligiblenon-spontaneous < 50%reactants favoured < 50%reactants favoured > 50%products favoured > 50%products favoured > 99.9%quantatative-----> > 99.9%quantatative-----> > < > <

Equilibrium Position lies “to the left” lies “to the left” more reactants more reactants less products less products lies “to the right” lies “to the right” less reactants less reactants more products more products If reactants are mixed and concentrations do not change could already be at equilibrium reaction rates are so slow that change is too difficult to detect

ICE Tables are used to organize data and calculations are used to organize data and calculations Initial, Change, Equilibrium Initial, Change, Equilibrium see sample 15.1 p. 681 see sample 15.1 p. 681

Homework Text p682 #4 & 6 Text p682 #4 & 6 Define the following phase equilibrium solubility equilibrium chemical reaction equilibrium forward rxtn reverse rxtn