Aim: What factors affect rate of reactions? DO NOW: What does the word “rate” mean? What would affect the rate of reaction? What would speed up a reaction?

Terminology Rate of reaction- how fast, how many moles are produced or consumed in a unit of time Collision Theory- rate of reaction depends on how often collisions occur and how many of them are effective Activation Energy- smallest amount of energy needed to start a reaction Activated Complex- an intermediate or transitional structure formed during the course of reaction

Collision Theory For a reaction to happen, the particles must have effective collision; particles must have enough energy and collide at the correct angles. The collision theory explains the factors that affect the rate of reactions.

Activation Energy Particles need enough energy to overcome the activation energy, the smallest amount of energy needed to start a reaction. ALL REACTIONS need to absorb energy to overcome the activation energy. However, exothermic reactions release more energy than initially absorbed. When the particles have absorbed enough energy they form an activated complex.

Factors that Affect Rate of Reaction Concentration More concentration  more collisions For gases increase in pressure  increases concentration  increases rate of reaction 2. Temperature increase in temperature  more K. E. (particles move faster)  more collisions 3. Surface Area increases surface area more exposed particles  more collisions

Factors that Affect Rate of Reaction 4. Nature of Reactants Ionic substances react faster than molecules; involve less rearrangement during a reaction. 5. Catalysts Lowers activation energy; particles need less energy to react

*Catalyst does not affect ΔH; there is no difference in ΔH.*

Summary Ionic compounds More concentration More pressure (gas) Faster rate of reaction High Temperature More Surface Area Catalyst

1. Consider the following reaction 1. Consider the following reaction. Mg(s) + 2H2O (l) --> Mg(OH)2 + H2(g) For the reaction to occur at the fastest rate, 1g of Mg (s) should be added in the form of 1) large chunks 3) a ribbon 2) small chunks 4) a powder 2. Raising the temperature speeds up the rate of chemical reaction by increasing 1) the effectiveness of the collisions only 2) the frequency of the collisions only 3) both the effectiveness and frequency of the collisions 4) neither the effectiveness nor frequency of the collisions

3. Consider the following equation 3. Consider the following equation. Fe(s) + CuSO4(aq) --> Cu(s) + FeSO4(aq) The Fe reacts more rapidly when it is powdered because the increased surface due to powdering permits 1) increased reactant contact 2) decreased reactant contact 3) pressure to affect reaction rate 4) warmer solution to be used 4. If the pressure on gaseous reactants is increased the rate of the reaction is increased because there is an increase in the 1) temperature 2) volume 3) concentration 4) heat of reaction

Heat of Reaction *Reminder: Heat of reaction is the amount of heat given off or absorbed in a chemical reaction* ΔH = H (products) - H(reactants) Heat of Heat content Heat content of reaction of products reactants

Heat of Reaction for Exothermic Process If the products have less potential energy or heat content than the reactants, heat is given off and its is an exothermic reaction. ΔH = negative

Potential Energy Diagram (Exothermic)

Heat of Reaction for Endothermic Process If the products have more potential energy or heat content than the reactants, heat is absorbed and its is an endothermic reaction. ΔH = positive

Potential Energy Diagram (Endothermic)

1. The forward reaction above is endothermic or exothermic. 2 1. The forward reaction above is endothermic or exothermic? 2. Which lettered arrow represents the energy of the reactants for the forward reaction? 3. Which lettered arrow represents the energy of the reactants for the reverse reaction?

4. Which lettered arrow represents the energy of the products for the forward reaction? 5. Which lettered arrow represents the energy of the products of the reverse reaction? 6. Which lettered arrow represents the ΔH for the forward catalyzed reaction?

7. Which lettered arrow represents ΔH for the forward uncatalyzed reaction? 8. Which lettered arrow represents the ΔH for the reverse catalyzed reaction? 9. Which lettered arrow represents the ΔH for the reverse uncatalyzed reaction?

10. Which lettered arrow represents activation energy for the forward catalyzed reaction? 11. Which lettered arrow represents activation energy for the forward uncatalyzed reaction? 12. Which lettered arrow represents activation energy for the reverse catalyzed reaction?

13. Which lettered arrow represents activation energy for the reverse uncatalyzed reaction? 14. Which lettered arrow represents energy of the activated complex for the catalyzed reaction? 15. Which lettered reaction represents energy of the activated complex for the uncatalyzed reaction?

16. Which lettered arrow represents the difference between the activation energies of the catalyzed and the uncatalyzed reactions? 17. Which lettered arrow represents the difference between the activated complex for the catalyzed and the uncaltyzed reactions? 18. The reverse reaction is (a) endothermic or (b) exothermic.

Do Now: Fill in the blank spaces. Word Box: Catalyzed Uncatalyzed