Standard 8: Reaction Rate

1. Standard 8: Reaction Rate Chemistry Ms. Siddall

2. 8b: Factors affecting reaction rate There are 4 factors that affect the rate of a reaction: • Temperature: Increasing temperature = more energy = more collisions = more reactions

3. study question 1 • Why do changes in temperature affect reaction rate?

4. Concentration: Increasing concentration = more particles = more collisions = more reactions low concentration high concentration

5. study question 2 • What happens to the number of collisions when there is an increase in concentration?

6. Surface Area: Increasing surface area = more places to collide = more collisions = more reactions Reaction occurs only at the surface More surface area = More chance to react

7. study question 3 • 1. Which has more surface area? • A 1g sugar cube or 1g of granulated sugar • 2. Which would react faster?

8. Pressure (gases only): Increasing pressure = particles closer together = more collisions = more reactions low pressure higher pressure Increased pressure forces particles together

9. study question 4 • 1. How would you increase the rate of a gas reaction? • 2. Why does increasing pressure NOT help increase the rate of a liquid reaction?

10. Reaction mechanics • A reaction can only occur if: • Molecules collide • Molecules collide with enough energy • Molecules collide with the correct orientation Molecules must hit hard enough in just the right place

11. study question 5 • What are the conditions at the molecular level for a reaction to occur?

12. 8a: Measuring reaction rate Reaction rate = speed of reaction • Example • An explosion happens quickly • Rusting happens slowly • Reaction rate = change in concentration time • ∆[reactants] or ∆[products] time time • ∆ = change • [ ] = concentration

13. study question 6 • What is the rate of reaction when 5 moles of reactant is used in 10 seconds?

14. Reversible reaction: X  Y [X] X  Y concentration rate [Y] Y  X time time • As concentration decreases - Rate decreases • As concentration increases - Rate increases • When concentration is constant - Rate is constant

15. study question 7 • Describe how rate changes as concentration changes.

16. Reaction pathway • Reactions are not always spontaneous • Activation energy = energy needed for a reaction to happen Activation energy energy reactants products time

17. study question 8 • Paper burns in the presence of oxygen. Explain why this paper does not burst into flames.

18. Catalyst standard 8c: catalyst • A catalyst increases the rate of a reaction by lowering ‘activation energy’ • A catalyst is not used up in the reaction • Example: a catalytic converter allows CO to react more easily with O2 to make CO2 Reaction pathwaycopy diagram on page 547

19. study question 9 • In terms of ‘activation energy’, how does a catalyst increase the rate of reaction? • Does a catalyst affect the energy of reactants or products?

20. Standard 8d: the definition and role of activation energy in a chemical reaction. Honors. • Reactants must form an ‘activated transition complex’ • This requires energy = activation energy

21. Activated transition complex Reaction with catalyst energy reactants products time

22. study question 10 • 1. Which has a higher energy: • Reactants or Products? • 2. How does the catalyst affect the energy of the activated transition complex?