Slide 1

Reaction Kinetics and Equilibrium

Slide 2

Why do chemical reactions occur between some substances and not in others?

Slide 3

Chemical reactions occur so that the atoms in the elements involved attain a more stable state of being.

Slide 4

Collision Theory Collision theory molecules must collide with the proper orientation and sufficient energy to react.

Slide 5

Slide 6

Activation Energy The activation energy is the amount of energy required to break the bonds between the atoms of the reactants.

Slide 7

Slide 8

Condition Necessary for Reactions to Occur 1)Collision: Reactants must collide. 2) Orientation: The reactants must align properly to react. 3) Energy: The activation energy must be attained to react.

Slide 9

Energy in Chemical Reactions Many chemical reactions also produce energy changes. Definitions: System the reactants and products in the reaction Surroundings everything else around the reaction (eg air in the room, reaction flask)

Slide 10

Heat of Reaction Heat of Reaction (H) the amount of heat lost or gained in a reaction Heat of Reaction: H = H products H reactants

Slide 11

Exothermic Reactions Exothermic Reactions energy is produced by a reaction; energy flows from the system to the surroundings H is negative because the reaction loses heat.

Slide 12

Exothermic Reaction Graph

Slide 13

Endothermic Reactions Endothermic Reactions energy is gained by a reaction; energy flows from the surroundings into the system H is positive because the reaction gains heat.

Slide 14

Endothermic Reaction Graph

Slide 15

Slide 16

Classify the reaction: 2H 2 O + 572kJ -> 2H 2 + O 2 1.Exothermic 2.Endothermic

Slide 17

H of the reaction = -560kJ 1.Exothermic 2.Endothermic

Slide 18

After the reaction, your hand gets burnt from the heat. The reaction must be: 1.Exothermic 2.Endothermic

Slide 19

Heat Values in Chemical Reactions Heat of Reaction is a stoichiometric value and is proportional to the coefficients of the reactants and products. 2H 2 O + 572kJ -> 2H 2 + O 2 Therefore, for every 2 moles of water that react, 572kJ of energy are required.

Slide 20

Reaction Rate Reaction rate rate of disappearance of one of the reactants ( or the rate of appearance of one of the products) -Measured in = Molarity s Change in concentration (molarity) over time.

Slide 21

Factors Affecting Reaction Rate What factors could affect the rate that a reaction takes place?

Slide 22

Factors affecting reaction rate Temperature Pressure Surface Area exposed Concentration of reactants and products Catalyst

Slide 23

Temperature Temperature as temperature goes up, the average kinetic energy increases. As velocity goes up, more collisions occur. Temperature, rate

Slide 24

Slide 25

Factors Affecting Reaction Rate Pressure as the volume of a closed container decreases, the pressure of a gas increases, causing more collisions (P, rate )

Slide 26

Surface Area Surface area exposed As more surface area is exposed, more collisions can occur. Surface Area , rate Note: crunching up a piece of candy or crushing a tablet into a powder makes smaller pieces, which increases the surface area.

Slide 27

Concentration of Reactants If the reactants are more concentrated, there are more reactants present = more collisions. Concentration of Reactants , rate

Slide 28

Presence of a Catalyst a substance that increases the rate without being permanently changed - lowers activation energy

Slide 29

Also used: inhibitors tie up a reaction so that it does not occur (opposite of a catalyst) - preservatives - anti-rust agents

Slide 30

Properties of an Equilibrium Reaction Equilibrium systems are DYNAMIC (in constant motion) DYNAMIC (in constant motion) REVERSIBLE REVERSIBLE can be approached from either direction can be approached from either direction Equilibrium systems are DYNAMIC (in constant motion) DYNAMIC (in constant motion) REVERSIBLE REVERSIBLE can be approached from either direction can be approached from either direction

Slide 31

The Concept of Equilibrium Chemical equilibrium occurs when a forward reaction and its reverse reaction proceed at the same rate.

Slide 32

Chemical Equilibrium Fe 3+ + SCN - FeSCN 2+ After a period of time, the concentrations of reactants and products are constant. After a period of time, the concentrations of reactants and products are constant. The forward and reverse reactions continue after equilibrium is attained. The forward and reverse reactions continue after equilibrium is attained.

Slide 33

The Concept of Equilibrium As a system approaches equilibrium, both the forward and reverse reactions are occurring. At equilibrium, the forward and reverse reactions are proceeding at the same rate.

Slide 34

A System at Equilibrium Once equilibrium is achieved, the amount of each reactant and product remains constant even though the reaction is still occurring.

Slide 35

Depicting Equilibrium In a system at equilibrium, both the forward and reverse reactions are being carried out; as a result, we write its equation with a double arrow N 2 O 4 (g) 2 NO 2 (g)

Slide 36

Le Chteliers Principle If a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.

Slide 37

Look at the equation: N 2 (g) + 3H 2 (g) 2NH 3 (g) + energy How can changes in conc., temp, or pressure affect this reaction?

Slide 38

N 2 (g) + 3H 2 (g) 2NH 3 (g) + energy Increase reactant concentration, there are more collisions between reactants, so reaction shifts to the right, towards the products.

Slide 39

N 2 (g) + 3H 2 (g) 2NH 3 (g) + energy Increase in temperature affects both sides of reaction, but it will increase one side more than the other. Think of energy as a product, if we increase its concentration, the reaction will lean in the other direction to regain equilibrium.

Slide 40

N 2 (g) + 3H 2 (g) 2NH 3 (g) + energy Increase in pressure will demand the fewest moles of gas. Occurs with a reduction in volume. -In this example, products will be favored -If number of moles of gas are equal, pressure has no effect. -Only has an effect on gases. -Decrease in pressure will have the opposite effect.

Slide 41

N 2 (g) + 3H 2 (g) 2NH 3 (g) + energy Decrease in volume will demand the fewest moles of gas. -In this example, products will be favored -If number of moles of gas are equal, pressure has no effect. -Only has an effect on gases. -Increase in volume will have the opposite effect.