Lesson 1

Starter What makes “superglue” bond instantly while regular glue does not? What factors determine how quickly food spoils? Why do “glow sticks” last longer when stored in the freezer? How do catalytic converters remove various pollutants from car exhaust?

Lesson objectives Define the rate of a chemical reaction Know the factors that affect reaction rate Describe the effect of concentration changes on the rate of a reaction in terms of collision theory Explain why an increase in the pressure of a gas increases the rate of a reaction

Key words Rate of reaction Reaction kinetics Simple collision theory Activation energy

Definition Rate of reaction is the change in concentration of a reactant or product per unit time. Initial rate of reaction is the change in concentration of a reactant or product, per unit time at the start of the reaction when t = 0.

Chemical reaction rates A + B → Product [A] and [B] decrease with time as the [product] increases. A + B → Product [A] and [B] decrease with time as the [product] increases.

Chemical reaction rates

Why does the slope of the reaction decrease with time? The rate of reaction slows down over time because there are fewer reactant particles left. Chemical reaction rates

Why does [B] fall faster than [A]? What could be causing this? Chemical reaction rates

How fast a chemical reaction goes is affected by many factors. List four of these. Temperature Pressure Concentration Particle size Catalyst Temperature Pressure Concentration Particle size Catalyst Discuss in pairs how each factor affects the reaction rate and why. Factors affecting rate of a reaction

Lesson objectives Define the rate of a chemical reaction Know the factors that affect reaction rate Describe the effect of concentration changes on the rate of a reaction in terms of the simple collision theory Explain why an increase in the pressure of a gas increases the rate of a reaction

Simple Collision Theory Reactions can only occur when reacting particles collide with enough energy. This energy is called the activation energy. Molecules must also be correctly orientated for a reaction to occur. Most collisions do not result in reaction unless there is sufficient energy and correct orientation.

Concentration/ Pressure: As the concentration of reactants increases, so does the likelihood that reactant molecules will collide, the rate of reaction generally increase. Concentration/ Pressure: As the concentration of reactants increases, so does the likelihood that reactant molecules will collide, the rate of reaction generally increase. Factors affecting reaction rates There are fewer red particles in the same volume so there is less chance of a collision There are more red particles in the same volume so there is more chance of a collision so the reaction goes faster

Temperature: Food spoils more quickly at room temperature than in a refrigerator bacteria grow faster at RT than at lower temperatures Temperature: Food spoils more quickly at room temperature than in a refrigerator bacteria grow faster at RT than at lower temperatures simulation Chemical reaction rates At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy.

Lesson objectives Define the rate of a chemical reaction Know the factors that affect reaction rate Describe the effect of concentration changes on the rate of a reaction in terms of the simple collision theory Explain why an increase in the pressure of a gas increases the rate of a reaction

In groups of three do the graphs exercise on handout. Extension work: Crossword Past paper question Chemical reaction rates