Rates of reaction and simple collision theory

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 objectivesDefine the rate of a chemical reactionKnow 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 wordsRate of reactionReaction kineticsSimple collision theoryActivation 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.

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.

TemperaturePressureConcentrationParticle sizeCatalyst

Discuss in pairs how each factor affects the reaction rate and why.

Factors affecting rate of a reaction

Lesson objectivesDefine the rate of a chemical reactionKnow 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.

Factors affecting reaction ratesThere 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

simulation

Chemical reaction rates

At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy.

Lesson objectivesDefine the rate of a chemical reactionKnow 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:CrosswordPast paper question

Chemical reaction rates