Kinetics
Information Page
Broad definition of what we are considering
We focused primarily on the conceptual understanding of reaction kinetics in chemical systems. This includes how reaction rates are influenced by various factors, the interpretation of rate laws*, and the mechanisms of reactions. We did not focus on videos that exclusively solve mathematical problems involving reaction rates without addressing the conceptual aspects OR videos that just address collision theory and do not address any aspects of reaction rates.
*Note: Interpretation of rate laws connecting order to collisions and/or mechanism. It was not enough to say that you can only get the coefficients from the mechanism, there needed to be an explanation of how the coefficients are derived from the mechanism.
Johnstone's Triangle Elements
Kinetics Specific Criteria
| Element | Examples |
|---|---|
| Macroscopic | General Definition for Macro: things we can see (observations) OR specific measurements. Visual examples of chemical reactions with different rates (e.g., slow rusting of iron vs. fast combustion of gasoline, color changing reactions). Demonstrations of factors affecting reaction rates (e.g., temperature, concentration, catalysts). Note: Just showing a picture of things with different surface areas and saying that the one with more surface area will react faster falls under verbal only. |
| Symbolic |
General Definition for Symbolic: standardized, discipline-specific short-form representations that efficiently communicate significant information. It is a universal shorthand that bridges the macroscopic and particulate levels. Chemical equations showing reaction rates (e.g., rate laws). Graphs or diagrams illustrating reaction rates (e.g., concentration vs. time graphs). Reaction energy diagrams Equations involving reaction kinetics (e.g., rate = k[A]n[B]m). |
| Particulate | General Definition for Particulate: visual model that helps “visualize” arrangement, movement, interaction, or composition of matter as it relates to the concept of interest Particle depictions showing collisions between reactant molecules. Illustrations of transition states and intermediates at the particulate level. |
| Connection between levels |
Videos should make explicit connections between two or more levels for this to be
coded as present. For example, they could show the chemical reaction along with a
particle level drawing or animation. |
Core Ideas
| Core Ideas Elements | |
| Change and Stability in Chemical Systems | Energy |
|---|---|
|
Energy and entropy changes, the rates of competing processes, and the balance between opposing forces govern the fate of chemical systems.
Video needs to include:
|
Energy changes are either the cause or the consequence of change in chemical systems, which can be considered on different scales and can be accounted for by the conservation of the total energy of the system of interest and the surroundings.
Video needs to include:
|
| Particulate Nature of Matter | Electrostatic Bonding and Interactions |
|
Matter is comprised of individual particles and it is through interactions of these individual particles that materials exhibit their properties and undergo chemical reactions.
Video needs to include:
|
Attractive and repulsive electrostatic forces govern noncovalent and bonding interactions between atoms and molecules. The strength of these forces depends on the magnitude of the charges involved and the distances between them.
Video needs to include:
|
Casual Mechanistic Reasoning
Must have both How and Why?
Options 1-5 must all fully address the concepts of collision theory as well within the video (collision needs to occur with enough energy and correct orientation to be successful.)
Option 1: What is the effect of temperature on the rate of a reaction?
How: At higher temperatures, reactant molecules have more kinetic energy, leading to more frequent and energetic collisions. [Both more frequent and energy required.]
Why: Increased kinetic energy means that a greater proportion of collisions have enough energy to overcome the activation energy barrier, resulting in a higher reaction rate.
Option 2: What is the effect of a catalyst on the rate of a reaction?
How: Catalysts provide an alternative reaction pathway with a lower activation energy, allowing reactant molecules to convert into products more easily.
Why: By lowering the activation energy, catalysts increase the number of successful collisions, thereby speeding up the reaction without being consumed in the process.
Option 3: What is the effect of concentration on the rate of a reaction?
How: Higher concentrations of reactants lead to more frequent collisions between reactant molecules.
Why: Increased collision frequency means that more reactant molecules can have the opportunity to interact and form products, resulting in a higher reaction rate.
Note: Video needs to be talking about this in terms of a reaction. Saying that increasing concentration/pressure means more particles per unit area, thus more collisions and faster reaction without talking about collisions between reactants or talking about a specific reaction does not meet this.
Option 4: What is the effect of surface area on the rate of a reaction?
How: More surface area of solid reactants lead to more spots for collisions between reactant molecules.
Why: Increased collision frequency means that more reactant molecules can have the opportunity to interact and form products, resulting in a higher reaction rate.
Option 5: What causes a reaction to be fast or slow? [Not observed in any video.]
How: The rate of a chemical reaction is affected by the activation energy – amount of energy that particles need to collide with for a reaction to occur. Reactions with higher activation energies occur more slowly.
Why: For a reaction to occur, bonds have to break. Stronger bonds require more energy to break so reactions that involve breaking stronger bonds are slower.
Option 6: What determines the rate of a chemical reaction? [Not observed in an video.]
How: The rate of a chemical reaction is determined by the slowest step in the reaction mechanism.
Why: The slowest step in a mechanism has the highest total energy of any transition state throughout the process of converting reactants to products. Achieving this energy state will be least likely due to the higher required energy which will therefore limit how quickly products can be formed.
Scientific Practices
| Most Frequent Science Practices |
|---|
Developing and Using Models
|
Analyzing and Interpreting Data
|
Using Mathematics and Computational Thinking
|
Constructing Explanations and Engaging in Argument from Evidence
|
Multimedia Principles
Multimedia learning as knowledge construction: The goal of multimedia presentations is not only to present information but also to provide guidance for how to process the presented information – that is, for determining what to pay attention to, how to mentally organize it, and how to relate it to prior knowledge. We will categorize the videos along each of the following criteria (High and Low should be mutually exclusive.)
| High | Low |
|---|---|
|
|
Misleading vs. Inaccuracies
- Several minor spelling issues is misleading, not inaccurate
- Significant personification is mislead
Example High Quality Videos
Examplar Videos
These are examples of videos that were found to provide good illustrations of some or many of the framework components for this concept. Develop a deep understanding of chemistry concepts requires multiple experiences with the material and these videos may provide one such experience.
|
Exemplar Video 1 |
Exemplar Video 2 |
Exemplar Video 3 |
|
Strengths The strengths of this video are that it uses a PhET simulation to show how energy and orientation are important for successful collisions and how increasing the temperature can speed up particles and result in more successful collisions. |
Strengths This video uses the framework of collision theory: to react, particles must collide, must collide with the correct orientation, and must collide with enough energy to overcome the activation energy barrier. For each factor, the video examines how changing it impacts each of these aspects of collisions to explain how reaction rate is affected. It also uses particle representations when explaining all factors. |
Strengths The video indicates that it will discuss factors affecting rates of reaction and then lists those factors to provide an organizing framework for the learner. Explanations for each factor are clearly delineated, and a summary is provided at the end. The video provides particle-level representations to support explanations, and the explanations are grounded in collision theory. |
|
Weaknesses The weakness of this video is that it only talks about how some factors, such as concentration, pressure, and surface area, can affect the rate of a reaction and does not actually show these in terms of particle interactions. It also tries to include several things in a relatively short video, which means the depth of explanation is not as strong as in some other videos. |
Weaknesses The particle representations are static. Given the dependence of reaction rate on collisions, using an animation to show moving particles and collisions could improve these explanations. |
Weaknesses Some segments of the video mix macroscopic and particulate-level representations, which could be misleading for students. For gases, instead of using round particles to represent atoms or molecules, the video uses clouds to represent gas particles. This could prompt students to think that gases are not matter made up of atoms or particles like solids or liquids. |
Click below to download a PDF version. Background image from PhET simulation Reaction and Rates.