Understanding Collision Theory: Factors Influencing Reaction Rates and Pathways
This instructional material covers Collision Theory, explaining factors leading to effective collisions and chemical reactions. It emphasizes that not all collisions result in a reaction due to requirements like sufficient energy and proper orientation. Students will learn to illustrate an endothermic reaction pathway, labeling reactants, products, the activated complex, activation energy, and enthalpy change. We also explore the role of catalysts in speeding up reactions by lowering activation energy and how concentration, temperature, and pressure affect reaction rates.
Understanding Collision Theory: Factors Influencing Reaction Rates and Pathways
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Presentation Transcript
WU 4/19 • Suggest at least two reasons why not all collisions result in a reaction. • Draw an endothermic reaction pathway LABEL: reactants, products, activated complex, activation energy, enthalpy change
Learning Goals • Explain the factors that lead to an effective collision and a chemical reaction • Describe the role of a catalyst in a chemical reaction. • Predict the effect of changes in concentration, temperature & pressure on reaction rate
Content Vocabulary • Collision • Orientation • Transition state • Activated complex • Activation energy • Reaction rate
Background Context • Collision Theory = Putting on Pants in the morning
18-1 Collision Theory • Effective collisions cause reactants to become products. • Not all collisions results in a reaction • Reactants must run into each other (collide) • Reactants must collide with enough energy • Reactants must collide with the proper orientation
Visualizing Collision Theory • 2HI H2 + I2 • Reactants Products • requires a transition state characterized by: • instability • high energy • Difficult to control • EX: Child Adult
Activated complex = teenagers • A transitional structure between reactants and products. • Old bonds break and new bonds are form. • unstable, high energy • All chemical reactions have an activated complex that must form. • Activation Energy: minimum energy needed to form the activated complex. • This is the bump on reaction graphs.
Depicting Reactions • Draw a reaction pathway for methane combusting. • Endothermic or exothermic? • Label the Reactants, Products, and activated complex on the graph • The ΔH is the net difference between products and reactants-- label this
Activation energy • The Eact is the energy from reactants to activated complex—label this • For methane combustion, what is the source of energy to reach the activated complex?
18-1 Reaction Rate • A measure of the decrease in reactants, or the increase in products over time. • Reaction rate depends on several factors: • Nature of reactants (will they react) • Temperature- • particles move faster (think bumper cars) • Concentration & Pressure of gases • more particles (think high school dance) • Surface area • More opportunities to react
18-1 Reaction Rates • *In general, the more times you get particles to collide, the higher the rate. • Catalyst: a substance that changes the rate of a reaction, and emerges unchanged • EX: enzymes to break down food. • EX: matchmakers • Increase the RATE of reaction. • Lowers activation energy • Make it easier for activated complex to form. • Emerge UNCHANGED from the reaction