Gas Law Information Page
Broad definitation of what we are considering
We considered primarily the conceptual understanding of how particulate motion gives rise to the relationships between volume, pressure, and temperature for samples of gases. It was fine to exclusively be addressing Ideal gases, without being explicit about the assumptions.
We did not code videos that just use the combined gas law (PV=nRT) or any of the individual relationships to solve mathematical problems without addressing any of the conceptual aspects.
Topic
- Either single gas law or Ideal gas law, not both
- Conceptual followed by calculations for videos that start with conceptual and then follow with practice problems using the gas laws
- If mainly conceptual with a single short problem thrown in the middle DO NOT use Conceptual followed by calculations
Johnstone’s Triangle Elements
Gas Law Specific Criteria
| Element | Examples |
|---|---|
| Macroscopic | Visible phenomena - balloons changing sizes at different temperatures, anything showing how macroscopic physical properties (V, T, P) of gases change when another variable is adjusted. This can be particulate representations that show macroscopic properties (e.g., increasing the temperature of a gas causing an increase in volume. If illustrating the relationship between P and another variable, there must be some measure of pressure to be macroscopic.) |
| Symbolic | Graphs that show how variables are related (e.g., P and V). PV=nRT or any other relationship equation. Other example, n with down arrow and V with down arrow to symbolically illustrate a relationship. (P↓ V↑) |
| Particulate | Particle representations of molecules oriented within a gas sample, showing significant distance between molecules. May involve animation showing molecules moving, or drawing indicating movement. Could show that different gases freely mix. |
| 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 particles within a drawing of a balloon
or other gas containing container and how changing temperature affects volume. However, to meet the connections criteria, there should be a verbal explanation. |
Core Ideas
Core Ideas Elements
| Change and Stability in Chemical Systems | Particulate Nature of Matter | Atomic/Molecular Structure & Properties |
|---|---|---|
|
Energy and entropy changes, the rates
of competing processes, and the
balance between opposing forces
govern the fate of chemical systems. |
Matter is comprised of individual particlesand it is through interactions of these individual particles that materials exhibit their properties and undergo chemical reactions. | The macroscopic physical and
chemical properties of a
substance are determined by the
three‐dimensional structure, the
distribution of electron density,
and the nature and extent of
noncovalent interactions between
the particles. |
| Video needs to include: Gas behaviour/properties are governed by gas particle motion. AND Changing one variable (P, V, T, or n) causes changes in the particle motion which results in changes in other variables.
Does not need to include discussion of particle collisions to meet CI but CMR DOES require discussion of particle collisions. |
Video needs to include: A description of how Kinetic molecular theory can be used to explain the properties of gases (gas particles travel in straight lines until they hit other gas particles or the walls of the container, volume of particles is negligible compared to total volume, particles collide elastically, speed of particles is dependent on temperature, attractive forces between particles are negligible). This includes stating that the pressure of a gas arises from collisions of the particles with the walls of the container. |
Video needs to include: Describes how the particulate nature (having volume and IMFs) causes real gases to deviate from the Ideal Gas Law predictions. |
| Sample Video | Sample Video | Sample Video |
Casual Mechanistic Reasoning
Must have both How and Why!
Option 1: What happens to one ideal gas property (P, V, T, n) when there is a change in another (assuming the others are kept constant)?
How?
- Correctly describes how the change in the first variable will change the particulate motion related to second variable. For example:
- increasing the volume of container will require gas particles to travel farther before hitting a wall of the container, or
- increasing temperature will cause molecules to move faster.
Why?
- Explanation should clearly articulate why that change will affect the second variable in the way that it does, based on the particulate collisions within the walls. For example:
- the increased volume of the container will result in fewer collisions with the wall and thus a lower pressure, or
- that the faster moving particles will have more collisions with the wall and greater force, which will increase the pressure (or in a flexible container, expand the size of the container until the internal and external pressures are equal.)
- OR If pressure is constant, decreasing the temperature will result in fewer collisions with the walls causing the pressure inside to be less than the pressure outside which will in turn result in a decrease in volume until the external and internal pressures are again equal.
Option 2: What explains deviations from ideal gas behaviour (real gases)?
How?
- Real gases frequently do not meet the expectations for ideal gases, e.g., have pressures that are lower or higher than what would be predicted by the ideal gas law, because gas particles do possess some volume and exhibit some IMFs with other particles in the gas phase.
Why?
- Especially at high pressures (low volumes), the volume of real gases will decrease the “empty space” available to ideal gases which means that the predicted pressure will be lower than the actual pressure.
- Especially at low temperatures, the IMFs of real gases will cause molecules to sometimes stick together and decrease the effective number of particles in the systems. This means the predicted pressure will be higher than the actual pressure.
Must address both aspects of the why?
Scientific Practices
| Most Frequent Science Practices |
|---|
SP 2: Developing and Using Models
|
SP 4: Analyzing and Interpreting Data
|
SP 5: Using Mathematics and Computational Thinking
|
SP 6: 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
Example Quality Gas Law 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 |
|
Comments Gives graphical depiction of relationship between P and V. States Boyles Law. Shows container with piston and pressure guage and particles in it. Shows how when you decrease the V the particles hit the walls of the container more frequently and P goes up. Moves to mathmatical relationship PV = k and then a couple of example problems using P1V1 = P2V2. Then ends with other gas laws. |
Comments Defined gas properties, discussed how changing one property affected another using particle motion (visually and verbally), connects to individual gas laws, presents combined gas law and ideal gas law, gives some practice using ideal gas law to do calculations. |
Comments The video briefly explains the differences between real gases and ideal gases and how to apply to kinetic molecular theory to ideal gases. |
|
Strengths This video effectively uses and connects the different levels of representation to help the viewer understand Boyle's Law. In the initial overview of the concept, the narrator makes connections to the core idea of Change and Stability in how she connects the impact of volume changes on the resultant pressure using the science practice of developing and using models. |
Strengths This video addresses multiple core ideas (Change and Stability and the Particulate Nature of Matter) while also engaging in a Science Practice of Using Mathematical and Computational Thinking. Further, the presenter provides causal mechanistic reasoning when explaning how different gas properties interrelate. |
Strengths This video uses strong particle representations to help make connections to the macroscopic and particulate level representations. Further, the narrator makes clear connections to the core ieas of Change and Stability and the Particulate Nature of matter. The video also provide Causal Mechanistic Reseoning related to why real gases deviate from ideal behavior. This video exhibits strong organizational characteristics with an overview on the front end and a summary at the back end. |
|
Weaknesses The organizational flow could have been improved to better help the viewer understand the key points and provided a clearer summary at the end. |
Weaknesses The organizational flow could have been improved to better help the viewer understand the key points and provided a clearer summary at the end. |
Weaknesses The video has the speaker on screen throughout the video, which can be distracting. Also, at 7:49 an equation that is not always true is put on the screen. |
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