Reaction Rates Quiz Thurs, March 10

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. 2

Measuring Reaction Rates Change in Electrical Conductivity Change in Color Change in Pressure Change in Volume 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

Factors that Effect Reaction Rate Concentration of Reactants The more particles, the more collisions As concentration increases, rate increases 5

Factors that Effect Reaction Rate Temperature of Reactants As temperature increases, particles move faster; there are more high-energy collisions 6

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 7

Factors that Effect Reaction Rate Pressure – Gases only! As pressure increases the concentration increases, so you will have more collisions 8

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 for the body (digestion, metabolism, contact cleaner) Catalytic converters (platinum, palladium, rhodium, etc. plates that convert toxic gases to less harmful products like NO → N2 + O2 and CO → CO2) 9

Catalyst 10

Factors that Effect Reaction Rate Inhibitors Compounds added to a reaction that slow it down Examples: Lead in diesel, preservatives in food. 11

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? 12