The Collision Theory and Activation Energy Explaining how

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The Collision Theory and Activation Energy Explaining how and why factors affect reaction rates

The Collision Theory and Activation Energy Explaining how and why factors affect reaction rates

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms • Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv 2)

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms • Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv 2)

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic

The Maxwell-Boltzmann apparatus • Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms • Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv 2)

The Maxwell-Boltzmann distribution • The resulting disk looks like this: Basically, if we plot

The Maxwell-Boltzmann distribution • The resulting disk looks like this: Basically, if we plot the intensity of the dots on a graph we get a graph of fraction of atoms/molecules vs. kinetic energy: Fraction of molecules Molecules hit disk last Molecules hit disk first Kinetic energy

Why is the graph skewed? • This curve is characteristic of all molecules •

Why is the graph skewed? • This curve is characteristic of all molecules • The curve is elongated due to how atoms collide, and to the units of the graph • Recall particles are in motion. An average speed will be reached. • The graph is skewed because 0 is the lower limit, but theoretically there is no upper limit • More than that the graph is skewed because the x-axis has units of energy not velocity Same data, different axes. E. g. v=1, KE=1 v=2, KE=4 v=3, KE=9 KE velocity

Temperature and reaction rate • By understanding the Maxwell-Boltzmann distribution, we can begin to

Temperature and reaction rate • By understanding the Maxwell-Boltzmann distribution, we can begin to understand the two reasons why an increase in temperature causes an increase in reaction rate • Read pg. 754 - 755 (starting at 18. 7), answer questions 18. 61 - 18. 64 on pg. 773 and … Q- Look back at the five factors that affect reaction rates. Three of these factors can be (at least in part) explained by the collision theory. Identify the 3 factors and explain how the affect of each can be explained with reference to the collision theory

Temperature and reaction rate 18. 61 Rates are typically 2 -3 times greater 18.

Temperature and reaction rate 18. 61 Rates are typically 2 -3 times greater 18. 62 Rate is proportional to the number of collisions per second among reactants 18. 63 reactant orientation and activation energy 18. 64 This happens because a larger fraction of the reactant molecules possess the minimum energy necessary to surpass Ea. A- Ability to meet (molecules that are well mixed will have a greater chance of colliding) Concentration of reactants (more molecules means more collisions) Temperature (faster moving molecules means more collisions per unit of time). Plus…

Temperature and reaction rate • Demonstrations: Mg + O 2, H 2 + O

Temperature and reaction rate • Demonstrations: Mg + O 2, H 2 + O 2 • By increasing the temperature, a small number of molecules reach Ea. The reaction is exothermic, further increasing temperature and causing more molecules to reach Ea, etc. • Draw the M-B distribution for H 2 + O 2 before heat was applied. Show heat affects the diagram. Shift due to higher Fraction of molecules temperature Kinetic energy Ea

Transition state theory • Read remainder of 18. 7 (pg. 756 – 757) For

Transition state theory • Read remainder of 18. 7 (pg. 756 – 757) For more lessons, visit www. chalkbored. com

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