Reactivity 2.2 How fast? The rate of chemical change
Reactivity 2.2.1
Understandings:
  • The rate of reaction is expressed as the change in concentration of a particular reactant/product per unit time.
Learning outcomes:
  • Determine rates of reaction.
Additional notes:
  • Calculation of reaction rates from tangents of graphs of concentration, volume or mass against time should be covered.
Linking questions:
  • Tool 1, 3, Inquiry 2 Concentration changes in reactions are not usually measured directly. What methods are used to provide data to determine the rate of reactions?
  • Tool 1 What experiments measuring reaction rates might use time as i) a dependent variable ii) an independent variable?
This video covers how to calculate the rate of reaction from a graph. 
This video covers rate of reaction graphs.
Reactivity 2.2.2
Understandings:
  • Species react as a result of collisions of sufficient energy and proper orientation.
Learning outcomes:
  • Explain the relationship between the kinetic energy of the particles and the temperature in kelvin, and the role of collision geometry.
Linking questions:
  • Structure 1.1 What is the relationship between the kinetic molecular theory and collision theory?
This video covers the relationship betwen temperature (in K) and kinetic energy. 
This video covers collision theory. 
Reactivity 2.2.3
Understandings:
  • Factors that influence the rate of a reaction include pressure, concentration, surface area, temperature and the presence of a catalyst.
Learning outcomes:
  • Predict and explain the effects of changing conditions on the rate of a reaction.
Linking questions:
  • Tool 1 What variables must be controlled in studying the effect of a factor on the rate of a reaction?
  • Nature of science, Tool 3, Inquiry 3 How can graphs provide evidence of systematic and random error?
This video covers the factors that affect the rate of reaction. 
Reactivity 2.2.4
Understandings:
  • Activation energy, Ea, is the minimum energy that colliding particles need for a successful collision leading to a reaction.
Learning outcomes:
  • Construct Maxwell–Boltzmann energy distribution curves to explain the effect of temperature on the probability of successful collisions.
This video covers activation energy. 
Reactivity 2.2.5
Understandings:
  • Catalysts increase the rate of reaction by providing an alternative reaction pathway with lower Ea.
Learning outcomes:
  • Sketch and explain energy profiles with and without catalysts for endothermic and exothermic reactions.
  • Construct Maxwell–Boltzmann energy distribution curves to explain the effect of different values for Ea on the probability of successful collisions.
Additional notes:
  • Biological catalysts are called enzymes.
  • The different mechanisms of homogeneous and heterogeneous catalysts will not be assessed.
Linking questions:
  • Reactivity 2.3 What is the relative effect of a catalyst on the rate of the forward and backward reactions?
  • Structure 3.1 (HL) What are the features of transition elements that make them useful as catalysts?
This video covers the effect of a catalyst on the rate of reaction.