Why do study gas laws? What are the practical applications? Whenever we inhale or exhale, that’s Boyle’s gas law in operation. When a hot air balloon rises, that’s Charles’ gas law in action.
How about air conditioner in your car or home: They compress a gas and pipes this high pressure gas into a radiator where it expands and turns cold. This then cools the air flowing past the radiator fins. That cooled air is then directed to your car or house.
And how did get to school or work today? Probably on a car or bus, which are machines powered by internal combustion engines. They literally have explosions of gas inside cylinders, converting chemical and electrical energy into the energy of motion.
Many folks use scuba diving, which involves a critical knowledge of how to combine and pressurize gases in order to keep divers safe – and especially to avoid life-threatning conditions such as the bends.
Another good introduction – Putting Gases to work. An intro to the idea of gas laws (ChemistryLand)
In this unit we’re going to make a useful simplification – we’ll treat gas as if it is “ideal.”
What is an ideal gas?
* Gas made of very small particles (atoms or molecules.)
* the total volume of the individual gas molecules is negligible compared to the volume of the container that they’re in.
* Average distance between particles is large compared to their size.
* Particles all have the same mass.
* They are in constant, random, rapid motion.
* They constantly collide among themselves, and with walls of the container.
* All the collisions are elastic.
* Gas molecules are considered to be perfectly spherical
* When not colliding, the particles don’t exert any forces on each other.
Are real world gases ideal like this?
Not at all. But these are useful simplifying assumptions; they make it much easier to derive mathematical rules for how gases work.
The practical results are the same as what we’d get using the more exact (but way more complicated) analysis.
Under most conditions – including all the weather that you have ever experienced – gases do behave like ideal gases.
When do these ideal gas assumptions fail? At very pressure, or very high temperature.
This Java applet is a simulation that demonstrates the kinetic theory of gases. The color of each molecule indicates the amount of kinetic energy it has: App: Gas molecule simulation falstad.com/gas
The gas laws
Charles’s law: volume and temperature
Gay-Lussac’s law (Amontons’s law)
The ideal, or combined, gas law
PV = nRT . or PV / T = constant
Advanced Placement gas topics
Dalton’s law of partial pressure
In a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
How does gravity affect gas?
Use this app Falstad.com/gas
How do we pull liquids up through a straw?
“Suction” doesn’t exist? Suction is really just a difference in air pressure. (more TBA)
Does hot air really rise?
A hot air balloon rises because the air pushing on the bottom of the balloon has a greater force than the downward force of the air on top of the balloon plus the balloon’s own weight. More TBA
The triple point
Not all gases have the same density – and we can see this clearly!
Apps and animations
Massachusetts Science and Technology/Engineering Curriculum Framework
8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed.
HS-PS2-8(MA). Use kinetic molecular theory to compare the strengths of electrostatic forces and the prevalence of interactions that occur between molecules in solids, liquids, and gases. Use the combined gas law to determine changes in pressure, volume, and temperature in gases.
Next Generation Science Standards
5-PS1-1. Develop a model to describe that matter is made of particles too small to be seen
Disciplinary Core Ideas: Matter of any type can be subdivided into particles that are too small to see, but even then the matter still exists and can be detected by other means. A model showing that gases are made from matter particles that are too small to see and are moving freely around in space can explain many observations, including the inflation and shape of a balloon and the effects of air on larger particles or objects. (5-PS1-1)
MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
College Board Standards
Objective C.1.5 States of Matter
C-PE.1.5.1 Translate among macroscopic (e.g., a beaker of water), symbolic [e.g., H2 O(s)], and atomic–molecular level representations of states. Describe, using representations, the relative arrangement of particles in solids, liquids and gases. Or conversely, identify the state of matter depicted in atomic–molecular level pictures or animations.
C-PE.1.5.2 Explain why gases expand to fill a container of any size, while liquids flow and spread out to fill the bottom of a container and solids hold their own shape. Justification includes a discussion of particle motion and the attractions between the particles.
C-PE.1.5.3 Investigate the behavior of gases. Investigation is performed in terms of volume (V ), pressure (P ), temperature (T ) and amount of gas (n) by using the ideal gas law both conceptually and mathematically.
C-PE.1.5.4 Explain natural phenomena (e.g., cold air escaping from a tire or low atmospheric pressure on rainy days) in terms of the kinetic–molecular theory of gases.
C-PE.1.5.5 Construct atomic–molecular level representations of changes that occur when thermal energy is added to a pure substance. Explain, using these representations, why the continuous addition of thermal energy to a pure substance will generally result in a change of state (not a chemical reaction).
C-PE.1.5.6 Explain, in terms of molecular motion, why liquid water expands when it freezes, whereas most substances expand when heated (e.g., mercury in a thermometer). Provide examples of instances where the expansion of water upon freezing is important (e.g., ice floating on water acts as an insulator in ponds to keep temperature of the rest of the water above freezing).
Common Core Math
Analyze proportional relationships and use them to solve real-world and mathematical problems.
Recognize and represent proportional relationships between quantities.
Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.
Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.
“Is the NGSS Going to Ruin High School Chemistry?” By Pete A’Hearn and Wanda Battaglia, California Classroom Science, 10/19/2015 http://www.classroomscience.org/is-the-ngss-going-to-ruin-high-school-chemistry