Regents Chemistry

1. Regents Chemistry • KINETICS

2. What is Kinetics? • Kinetics is the branch of chemistry that deals with rates of chemical reactions • Different factors affect how quickly chemical reactions occur • In order for a reaction to occur, reactant particles must collide • This is called COLLISION THEORY • Reactions occur between collisions of particles that are orientated correctly and have sufficient amounts of energy-ACTIVATION ENERGY!!!!!

3. 1- Correct orientation 2- Sufficient activation energy!!! 1- Wrong orientation or not enough activation energy. 2- ACTIVATION ENERGY: the minimum amount of energy needed to form the activaion complex and start a reaction. : Kinetic energy is converted to potential energy

4. Why is Kinetics Important? • Kinetics allows chemists to predict how fast a reaction will occur • Important in the synthesis of all kinds of compounds • In manufacturing, it is essential to making products, • timing rates between chemical reactions to get a desired product

5. What Factors Affect Rate of Reaction? • The rate of a chemical reaction depends on a number of factors that affect the number of effective collisions between particles • Nature of Reactants • Concentration • Surface Area • Pressure • Temperature • Presence of a Catalyst

6. Nature of Reactants • Reactions involve the breaking of existing bonds and the formation of new bonds • Generally, covalently bonded substances are slowerto react than ionic substances as they have move bonds to be broken • Breaking more bonds requires that the particles must have more energy when they collide

7. Concentration • Most chemical reactions will proceed at a faster rate if the concentration of one or more of the reactants is increased • Ex: Combustion of Paper • Normal air is 20% oxygen, if we use pure oxygen it burns much faster! • Why? KMT says that more collisions between oxygen and paper particles = faster rate of reaction!

8. 1- The greater concentration of reactants, the more collisions 2- Increase concentration = increase collisions = increase rate of reaction!!! Chemical reaction is faster!!!

9. TEMPERATURE 1- Increase in temperature = increase in rate of reaction 2- WHY? ANS: increase in kinetic energy and motion of particles- more collisions of particles

10. Surface Area • When more surface area of a substance is exposed, there are more chances for reactant particles to collide • Ex: one centimeter of a cube of Mg reacting with HCl reacts more slowly then increasing the surface area by breaking Mg down into smaller pieces

11. INCREASING SURFACE AREA

12. Pressure • Pressure has little or no effect on rates of reactions between liquids and solids… • It does have an effect on gases! • An increase in pressure has the effect of increasing the concentration of gaseous particles • Therefore, it increases the rate of a reaction that involves only gases

13. Presence of a Catalyst • Catalysts are substances that increase the rate of a reaction, by providing an alternative pathway • Catalysts take part in a reaction, but they are unchanged when the reaction is complete • So they are present in the reactants and products and only assist in the rate of the reaction

14. Temperature • By definition, temperature implies that the greater the temperature, the faster the molecules will move (higher kinetic energy) • When particles are moving faster, more collisions occur and increasing the likelihood of a reaction • Higher Temp = particles with more kinetic energy = more effective collisions

15. Regents Chemistry • Potential Energy Diagrams

16. What’s Potential Energy? • Chemical bonds are large sources of chemical potential energy (when bonds are formed) • CHEMICAL ENERGY: energy associated with the breaking and forming of chemical bonds • This is a form of Potential energy!

17. Chemical Bonds Have PE! • Chemical bonds have large supplies of potential energy • Bonds are broken in chemical reactions and new bonds form in products • Energy can be released or gained in these chemical reactions, so… • Potential energy can be increased or decreased depending on the reaction..

18. -ENERGY IS ON REACTANT SIDE! -ENERGY RELEASED: ON PRODUCT SIDE!!!!

19. What’s a PE Diagram?..First look • A PE diagram illustrates the potential energy change that occurs during a chemical reaction Activated Complex Reaction Coordinate = progress of reaction Reactants --- Potential energy Products Reaction Coordinate

20. Potential Energy Diagrams • In order for a reaction to occur, the reactants must have sufficient energy to collide effectively • As reactant particles approach each other, kinetic energy is converted into potential energy • The molecules must also have proper orientation to come together…this leads to..

21. Activated Complex • When molecules collide with the proper orientation, an intermediate product is formed • Activated Complex – is a temporary, intermediate product that may either break apart and reform the reactants or rearrange the atoms and form new products

22. Example of Collisions • HI molecules collide in a reaction and form H2 and I2 products

23. Reactants and Products on a PE Diagram Activation energy Difference In PE H = Heat of reaction A + B  C + D + Heat Heat is a product because the PE is lower for the products than in the reactants

24. Activation Energy and Heat of Reaction • The amount of energy needed to form the activated complex from the reactants is called the activation energy • The diagram is typically read from left to right and vice versa • So..we specify by saying forward or reverse • HEAT OF REACTION – is the heat required to form products or reactants in this specific reaction • Can be negative or positive depending on viewing the reaction as forward or reverse

25. The Effect of a Catalyst • Catalysts are added to a reaction to lower the activation energy, which in turn speeds up the reaction • The catalyst speed up the reaction by providing a new pathway • In turn, the activation energy of the reverse reaction is also lowered…but • The H remains unaffected..see why

26. Effect of a Catalyst What does 5 represent?

27. Two Outcomes of PE Diagrams • 1. PE of products is lower than the reactants, so energy is lost and released to the environment – Exothermic! (H = -)

28. Two Outcomes of PE Diagrams • PE of the products is greater than the reactants, so energy is absorbed to make the products – Endothermic (H = +)