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To understand the collision model of chemical reactionsTo understand activation energy To understand how a catalyst speeds up a chemical reaction To explore reactions with reactants or products in different phases To learn how equilibrium is established To learn about the characteristics of chemical equilibrium Objectives 17.1Reaction Rates and EquilibriumEquilibrium1Big Idea 4Rates of chemical reactions are determined by the details of the molecular collisionsEquilibriumA. How Chemical Reactions Occur Collision model molecules must collide in order for a reaction to occur Rate depends on concentrations of reactants and temperature.

Equilibrium3A. How Chemical Reactions Occur Many reactions proceed via a series of elementary reactionsElementary reactions are mediated by collisions between molecules. Only collisions having sufficient energy and relative orientation of reactants lead to productsEquilibriumB. Conditions That Affect Reaction Rates Concentration increases rate because more molecules lead to more collisions Temperature increases rate Why?

Equilibrium5B. Conditions That Affect Reaction Rates Reaction rates that depend on temperature and other environmental factors are determined by measuring changes in concentrations of reactants or products over timeEquilibriumB. Conditions That Affect Reaction Rates Catalyst a substance that speeds up a reaction without being consumed Enzyme catalyst in a biological system

Equilibrium8CatalystReaction rates may be increased by the presence of a catalystCatalysts function by lowering the activation energy of an elementary step in a reaction mechanism, and by providing a new and faster reaction mechanismImportant classes in catalyst include acid-base catalysis, surface catalysis, and enzyme catalysisEquilibriumC. Heterogeneous Reactions Homogeneous reaction all reactants and products are in one phase Gas Solution Heterogeneous reaction reactants in two phases

Equilibrium10C. Heterogeneous Reactions

Equilibrium11D. The Equilibrium Condition Equilibrium the exact balancing of two processes, one of which is the opposite of the other

Equilibrium12D. The Equilibrium Condition Chemical equilibrium a dynamic state where the concentrations of all reactants and products remain constant

Equilibrium13E. Chemical Equilibrium: A Dynamic Condition

Equal numbers of moles of H2O and CO are mixed in a closed container.

The reaction begins to occur, and some products (H2 and CO2) are formed.

The reaction continues as time passes and more reactants are changed to products.

Although time continues to pass, the numbers of reactant and product molecules are the same as in (c). No further changes are seen as time continues to pass. The system has reached equilibrium.

Equilibrium14E. Chemical Equilibrium: A Dynamic Condition Why does equilibrium occur?

Equilibrium15To understand the law of chemical equilibrium To learn to calculate values for the equilibrium constant To understand how the presence of solids or liquids affects the equilibrium expression Objectives 17.2Characteristics of EquilibriumEquilibrium16Big Idea 6Any bond or intermolecular attraction that can be formed can be broken. These two processes are in a dynamic competition, sensitive to initial conditions and external perturbations.EquilibriumA. The Equilibrium Constant: An Introduction Law of chemical equilibriumFor a reaction of the type Each set of equilibrium concentrations is called an equilibrium position. aA + bB cC + dD Equilibrium expression

Equilibrium18A. The Equilibrium Constant: An Introduction Chemical equilibrium is a dynamic, reversible state in which rates of opposing processes are equalSystems at equilibrium are responsive to external perturbations, with the response leading to a change in the composition of the systemEquilibriumB. Heterogeneous Equilibria Heterogeneous equilibria an equilibrium system where the products and reactants are not all in the same state

Equilibrium20To learn to predict the changes that occur when a system at equilibrium is disturbed To learn to calculate equilibrium concentrations To learn to calculate the solubility product of a salt To learn to calculate solubility from the solubility product Objectives 17.3Applications of EquilibriaEquilibrium21A. Le Chateliers Principle Le Chateliers Principle when a change is imposed on a system at equilibrium the position of the equilibrium shifts in a direction that tends to reduce the effect of that change Equilibrium22A. Le Chateliers Principle Effect of a Change in Concentration

Equilibrium23A. Le Chateliers Principle Effect of a Change in Concentration When a reactant or product is added the system shifts away from that added component. If a reactant or product is removed, the system shifts toward the removed component.Equilibrium24A. Le Chateliers Principle Effect of a Change in Volume

The system is initially at equilibrium.

The piston is pushed in, decreasing the volume and increasing the pressure. The system shifts in the direction that consumes CO2 molecules, lowering the pressure again.

Equilibrium25A. Le Chateliers Principle Effect of a Change in Volume Decreasing the volumeThe system shifts in the direction that gives the fewest number of gas molecules.

Equilibrium26A. Le Chateliers Principle Effect of a Change in Volume Increasing the volume The system shifts in the direction that increases its pressure. Equilibrium27A. Le Chateliers Principle Effect of a Change in Temperature The value of K changes with temperature. We can use this to predict the direction of this change. Exothermic reaction produces heat (heat is a product) Adding energy shifts the equilibrium to the left (away from the heat term). Endothermic reaction absorbs energy (heat is a reactant) Adding energy shifts the equilibrium to the right (away from the heat term).

Equilibrium28B. Applications Involving the Equilibrium Constant K > 1 the equilibrium position is far to the right K < 1 the equilibrium position is far to the left The Meaning of K Equilibrium29B. Applications Involving the Equilibrium Constant The value of K for a system can be calculated from a known set of equilibrium concentrations. Unknown equilibrium concentrations can be calculated if the value of K and the remaining equilibrium concentrations are known. Equilibrium30C. Solubility Equilibria The equilibrium conditions also applies to a saturated solution containing excess solid, MX(s). Ksp = [M+][X] = solubility product constantThe value of the Ksp can be calculated from the measured solubility of MX(s). Equilibrium31C. Solubility Equilibria Chemical equilibrium plays an important role in acid-base chemistry and in solubilityThe equilibrium constant is related to temperature and the difference in Gibbs free energy between reactants and productsEquilibrium