3.3 b/c: Lesson: Rates of Reactions

Lesson: Rates of Reactions

Recap of content

Syllabus dot points

investigate the role of activation energy, collisions and molecular orientation in collision theory

explain a change in reaction rate using collision theory

What you need to know

• what reaction rate is

• what factors effect reaction rate, and how they do so

• what activation energy is

• explain collision theory, in reference to reaction rate/factors

• catalysts, in reference to reaction rate and collision theory

Multiple Choice

What is the rate of reaction?

• How fast a reaction is 
• How big a reaction is
• How loud a reaction is
• How much gas a reaction produces

Rate of a Reaction

• how long it takes for the reaction to reach completion (reactants used up, and products formed)

• therefore, rate of change of concentration of reactants and products

• we then have to determine what factors can effect the rate of a reaction

• alter the RR by increasing collisions, lowering AE, or changing molecular orientation

Collision Theory

• for a reaction to occur, particles have to collide and with enough energy and at the correct orientation

• percentage of successful collisions stays the same, but factors can increase the rate of successful collisions

Factors effecting reaction rate

• Increase SA, increase RR - more collisions

• Increase concentration, increase RR - more collisions

• Increase pressure, increase RR - more collisions

• Increase temp, increase RR - faster/more collisions & increase energy

• Catalyst - lowers AE or orientation

​Energy Profile Diagrams

• ​Energy vs progress of the reaction

• ​Demonstrates how much activation energy is needed

• Shows whether the reaction has more or less energy than when it started

  • What could this indicate? ​

Activation Energy

• minimum amount of energy reactants must have in order to undergo a reaction

• OR the energy difference between the reactants and products

• more rapid rate of reaction, the higher the activation energy

• catalysts can lower the AE by providing an alternative reaction pathway

How do catalysts work?

Catalysts lower the activation energy needed for a particular reaction, without being a part/being consumed in the reaction.

​

They can work in a number of ways:

• ​provides an alternative route for the reaction to proceed

  • reacting with a reactant to form ​an intermediate that requires less energy

• providing a surface for the reaction to proceed on that may weaken or break bonds - orienting the particles

Multiple Choice

Why does a higher temperature increase the rate of a reaction?

• it increases both the frequency and energy of particle collisions

• it only increases the frequency of particle collisions

• it only increases the energy of particle collisions

• it reduces the activation energy of the reaction

Multiple Choice

Why does a higher concentration increase the rate of reaction?

• it increases the amount of reactants

• it lowers the activation energy

• it increases the energy of particle collisions

• it increases the frequency of particle collisions

Multiple Choice

The following graph shows two different reaction pathways for the same overall reaction at the same temperature. Which pathway is slower and why?

• Red, because the activation energy is larger
• Blue, because the activation energy is lower
• both reaction progress at the same rate

Multiple Choice

When surface area is decreased the rate of reaction...

• Decreases, because there are LESS possible sites for correct collisions

• Increases, because there are LESS possible sites for correct collisions

• Decreases, because there are MORE possible sites for correct collisions

• Increases, because there are MORE possible sites for correct collisions

Endothermic vs Exothermic diagrams

• helps us with Module 4

• breaking bonds = absorbs energy

• forming bonds = releases energy

• endothermic = overall absorbs energy = therefore, right image

• exothermic = overall releases energy = left image

Multiple Choice

Is this diagram endothermic or exothermic

• Endothermic

• Exothermic

Poll

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