Unit 10: Energy in Chemical Reactions

1. Unit 10:Energy in Chemical Reactions Cypress Creek High School Chemistry 1L Chapter 10

2. Reaction Rate • Reaction Rate is the number of atoms, ions or molecules that react in a given time to form products • We measure either the rate of disappearance of the reactants or the rate of appearance of one of the products • In simpler terms: • The average rate is the change in a given quantity during a specific period of time.

3. Reaction Rate Graph • For the reaction H2 + I2 → 2HI, • What is happening to the concentration of the reactants? • What is happening to the concentration of the products?

4. Measuring Reaction Rates • Change in Electrical Conductivity • Change in Color • Change in Pressure • Change in Volume

5. Factors that Effect Reaction Rate • Physical State of the Reactants • The more freedom of movement, the more collisions • As state of matter changes from solid to gas, rate increases

6. Factors that Effect Reaction Rate • Concentration of Reactants • The more particles, the more collisions • As concentration increases, rate increases

7. Factors that Effect Reaction Rate • Temperature of Reactants • As temperature increases, particles move faster; there are more high-energy collisions

8. Factors that Effect Reaction Rate • Particle Size (surface area) • For solids, breaking up big pieces increases surface area, increasing rate by having more places for the molecules to interact • Ionic compounds have more surface area than covalent

9. Factors that Effect Reaction Rate • Pressure – Gases only! • As pressure increases the concentration increases, so you will have more collisions

10. Factors that Effect Reaction Rate • Catalysts – compounds added to speed up reaction but not used in the reaction. • Lowers activation energy but does not change ΔH • Examples: enzymes, catalytic converters (Pt, plates that convert NO → N2 + O2 and CO → CO2)

11. Catalyst

12. Catalysts Without a catalyst Enthalpy Time (min)

13. Catalysts Lowers activation energy Without a catalyst Enthalpy With a catalyst Time (min)

14. Catalysts • DOES THE CATALYST CHANGE THE DH? NO! Lowers activation energy Without a catalyst Enthalpy H reactants With a catalyst H products Time (min)

15. Factors that Effect Reaction Rate • Inhibitors • Compounds added to a reaction that slow it down • Examples: Lead in diesel, preservatives in food.

16. Reaction Rates Discussion • Why do you add lighter fluid to charcoal in a grill? • How does opening and closing air vents on a charcoal grill effect how fast the coals burn? • How can an explosion occur in a grain elevator when grain is not considered flammable?

17. Chemical ReactionsExample • Remember the classic science fair project - the homemade volcano? • It’s done by combining vinegar and baking soda (and some red food coloring for effect). • These substances undergo a chemical reaction, evident by the overflow and bubbles. • This reaction produces three new substances: water, carbon dioxide, and sodium acetate (used in hot packs) Reaction of baking soda and vinegar: http://www.metacafe.com/watch/706897/vinegar_grenade/