Unit 2: Dynamic Equilibrium Quiz 1 Topics ( H II.1-II.2) Definitions Requirements for an equilibrium to occur. Characteristics of a system in chemical equilibrium Defining the chemical equilibrium Constant.

Definitions Equilibrium: results when 2 opposing forces are in balance, and no observable changes in the system are occurring. Static Equilibrium: In a static equilibrium, there are no changes in the system at a microscopic or macroscopic level

Definitions Dynamic Equilibrium: is the situation in which the observable properties of the system are not changing, however, at the microscopic level the system is changing. Chemical equilibrium: a condition in which 2 chemical changes exactly oppose one another, in this situation the amounts of products and reactants does not change. Even though at a microscopic level products and reactants are being inter converted constantly.

Gottcha Equilibriums apply only to closed systems. An open system in which 2 opposing forces are balanced is said to be in a Steady State.

Characteristics of Chemical Equilibriums A system is in chemical Equilibrium if: The rate of consumption of the reactants equals the rate of production of the reactants ( The rate of the forward reactions equals the rate of the reverse reaction) The concentration (amount) of reactants and products is not changing over time.

Keq The Equilibrium Constant Keq, the equilibrium constant is defined as the ratio of the concentration of products divided by the concentration of reactants in a closed system

Keq Equilibrium Constant At the point of equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. Note 1: this does not imply that the concentrations of reactants and products are the same Note 2: all chemical systems that have 2 opposing forces end up in a chemical equilibrium.

Quiz II, Dynamic Equilibrium Entropy Estimating the entropy of a system Entropy vs. Enthalpy Predicting the spontaneity of chemical reactions

Enthalpy Vs. Entropy The forces that govern chemical reactions are enthalpy and entropy Recall: Enthalpy is the total energy in an open system, and that all systems tend towards their lowest energy state. A.K.A the law of laziness Entropy: is a measure of how disordered a system is. All systems tend towards a state of maximum disorder. A.K.A the law of messiness. Probability favours randomness and disorder.

Rules for “measuring” Entropy Entropy and State Solids are very orderly and pure crystals have zero randomness Pure liquids are much more random than solids as molecules are free to move Solutions are more random then pure liquids, as solutions contain more than one type of molecule that can be randomly distributed through out. Gases are much more random than solids, liquids or solutions as they can move freely and will distribute themselves randomly to fill a container The more particles there are in a system the greater the entropy the system will have.

Enthalpy,Entropy and Chemical Rx’s If Entropy and Enthalpy both favour the product side of a reaction, the reaction will go to 100% completion. If Entropy and Enthalpy both favour the reactant side of a reaction, the reaction will not occur. If Entropy and Enthalpy are on opposite sides of a reaction equation, then a chemical equilibrium will be established

Le Chatelier’s Principle II.4 p(50) Quiz 3 Definition Stressors for chemical systems Predicting the effects of a stressor on a chemical equilibrium

Le Chatelier’s Principle If a closed system at equilibrium is subjected to a change, processes will occur that tend to counter act that change Shift happens! When ever you try to change something you will encounter opposition. For every action there is an equal an opposite reaction.

Stressors for Chemical Systems in Equilibrium Temperature: Concentration of reagents or products Pressure for equilibriums involving gases. Volume for equilibriums involving gases

Gottcha The concentration of a pure substance (solid or liquid) is always a constant and set equal to 1 Adding a catalyst does not shift the position of an equilibrium (I.e. is not a stressors to a chemical system in equilbrium)

Industrial Applications of Le Chatelier’s Property The Haber Process for making Ammonia Making quick lime for cement

Keq and the equilibrium Position Recall: Keq= 1 Implies that the ratio of products to reactants is 1:1 Keq >1 implies the equilibrium favours product Keq <1 implies the equilibrium favours the reactant

Keq Quiz Writing the Keq formula Calculating Keq Calculating Keq concentrations Reaction Quotient/ Trial Keq’s Predicting which way an equilibrium will shift using keq’s

Keq formula the concentrations of pure solids/liquids is defined as 1 and do not appear in the Keq formula

Solving Keq Problems Balance Rx. Write Keq formula/equation Convert all given value to Mol/L Build an I.C.E table Solve the Keq equation