Chemical Equilibrium Rates of Reaction Equilibrium

Energy Rxn Progress 2H 2(g) + O 2(g)  2H 2 O + Energy Just because something has the potential to react doesn’t mean it will do so immediately. doesn’t mean it will do so immediately. Just because something has the potential to react doesn’t mean it will do so immediately. doesn’t mean it will do so immediately. H 2(g) O 2(g) may stay together for lifetime without reacting to form water. H 2(g) + O 2(g) may stay together for lifetime without reacting to form water. Reaction Rates Very stable product (  H < 0)  H

Chemical kinetics The study of reaction rates (speed) Kineticstime required KineticsMeasures the time required for a reaction to occur.

Chemical kinetics Kinetics of a chemical reaction can tell us - how long how long it will take for a reaction to reach completion. (mechanism how chemicals react to form products (mechanism). catalysts effects of catalysts and enzymes. how to control how to control a reaction.

Speed at which reactant is used up. Speed at which product forms. burning Oxidation: Paper burning Paper turning yellow rusting Oxidation: Nails rusting Reaction Rates Fast: Slow:

Figure 9.1 Reaction Rates Fast: Slow: Slower:

A reaction won’t happen if: Effective collisions aligned Molecules are not aligned correctly. energy to break bonds Insufficient energy to break bonds. N 2 O 2

3. They have to have enough E. For reactants to make products: collide 1. Molecules must collide (solvents really help) aligned 2. They have to be aligned correctly. (Parked cars don’t collide) Effective collisions

Activation Energy activation energy The activation energy E act Is the minimum energy needed for a reaction to take place upon proper collision of reactants.

Show the  E during a reaction. Show the  E during a reaction. Energy diagrams  H E act Activation energy E act Energy A temporary state where bonds are reforming. Activated Complex Activated Complex

Factors Influencing Rxn Rates Reaction rates can be affected by : polar vs. nonpolar 1. Reactant structure( polar vs. nonpolar ) physical state of reactants vapor vs liq ( vapor vs liq. ) 2. Concentration 2. Concentration of reactants medications ( medications ) surface area sugar cube vs crystals surface area ( sugar cube vs crystals ) 3. Temperature hypothermia & metabolism ( hypothermia & metabolism ) 4. Catalyst H 2 O 2 & blood 4. Catalyst ( H 2 O 2 & blood )

If reactant concentration Increase reactant concentrationthen # of collisions Increase # of collisionsso reaction rate Increase reaction rate. Reaction Rates Concentration : 1.More Reactants: More cars  More collisions

Reaction Rates Concentration: 1.More Reactants: 8 blocks: 34 surfaces 8 blocks: 24 surfaces More surface area  More collisions

Reaction Rates Temperature: 2.Higher Temperature: Faster cars  More collisions More Energy  More collisions Reacting molecules move faster, providing colliding molecules w/ E act.

Reaction Rates Catalyst: 3.Adding a Catalyst: Lower E act  More collisions Uncatalysed reaction

Reaction Rates Catalyst: 3.Adding a Catalyst: Lower E act  More collisions Uncatalysed reaction Catalysed reaction Lower activation energy Alters reaction mechanism but not products Is not used up during the reaction.

Reaction Rates Catalyst: 3.Adding a Catalyst: Lower E act  More collisions Uncatalysed reaction Catalysed reaction Lower activation energy Enzymes Enzymes are biological catalysts.

Catalytic Converter

Learning Check State the effect of each on the rate of reaction as (I) increases, (D) decreases, or (N) no change. A. Increasing the temperature. B. Removing some of the reactants. C. Adding a catalyst. D. Placing the reaction flask in ice. E. Increasing the concentration of a reactant.

Solution State the effect of each on the rate of reaction as (I) increases, (D) decreases, or (N) no change. A. Increasing the temperature.(I) B. Removing some of the reactants. (D) C. Adding a catalyst. (I) D. Placing the reaction flask in ice. (D) E. Increasing the concentration of a reactant. (I)

Learning Check Indicate the effect of each factor listed on the rate of the following reaction as (I) increases, (D) decreases, or (N) none: 2CO(g) + O 2 (g)  2CO 2 (g) A. Raising the temperature B. Removing O 2 C. Adding a catalyst D. Lowering the temperature

Solution Indicate the effect of each factor listed on the rate of the following reaction as (I) increases, (D) decreases, or (N) none: 2CO(g) + O 2 (g)  2CO 2 (g) A. Raising the temperature (I) B. Adding O 2 (D) C. Adding a catalyst (I) D. Lowering the temperature (D)

Equilibrium A state where the forward and reverse conditions occur at the same rate. Dynamic Equilibrium I’m in static equilibrium.

Chemical equilibrium Dynamic process Rate of forward Rxn = Rate of reverse Rxn H 2 O (l) H 2 O (g) H 2 O (l) H 2 O (g) (reactant) (product) (reactant) (product) Dynamic Equilibrium Concentration of reactants and products remain constant over time.

Equilibrium and reaction rates A point is ultimately reached where the rates of the forward and reverse reactions are the same. At this point, equilibrium is achieved. Reaction rate Time H 2 O (l) H 2 O (g) H 2 O (l) H 2 O (g) (reactant) (product)

Figure 9.8 2SO 2(g) + O 2(g) 2SO 3(g) At Equilibium SO 2(g) +O 2(g) Initially SO 3(g) Initially

Figure 9.9 2SO 2(g) + O 2(g) 2SO 3(g) At Equilibium SO 2(g) +O 2(g) Initially SO 3(g) Initially

Figure 9.10 N 2(g) + O 2(g) 2NO (g) At Equilibium N 2(g) +O 2(g) Initially NO (g) Initially

Equilibrium Concentration Time KineticEquilibrium Region Concentration of reactants and products remain constant over time.

[C]c [D]d[A]a [B]b[C]c [D]d[A]a [B]b K eq = Equilibrium constant (K) Equilibrium expression (for any reaction at constant temperature) aA + bB cC + dD moles per liter coefficients productsreactants

Figure 9.11 [C]c [D]d[A]a [B]b[C]c [D]d[A]a [B]b K eq = aA + bB cC + dD productsreactants Equilibrium constant (K)

N 2(g) + 3 H 2(g) 2 NH 3(g) K eq = [ NH 3 ] 2 [ N 2 ] [ H 2 ] 3 Equilibrium constant (K)