Thermal physics

11 hours


3.1 – Thermal concepts


Essential idea: Thermal physics deftly demonstrates the links between the macroscopic measurements essential to many scientific models with the microscopic properties that underlie these models.
Nature of science: Evidence through experimentation: Scientists from the 17th and 18th centuries were working without the knowledge of atomic structure and sometimes developed theories that were later found to be incorrect, such as phlogiston and perpetual motion capabilities. Our current understanding relies on statistical mechanics providing a basis for our use and understanding of energy transfer in science.
Understandings:
• Molecular theory of solids, liquids and gases States of matter basics States of matter
• Temperature and absolute temperature Race for absolute zero
• Internal energy Thermodynamics and internal energy
• Specific heat capacity Concept and example
• Phase change Concept
• Specific latent heat Concept and example Sample SHC and SLH problems
Applications and skills:
• Describing temperature change in terms of internal energy
• Using Kelvin and Celsius temperature scales and converting between them
• Applying the calorimetric techniques of specific heat capacity or specific latent heat experimentally
• Describing phase change in terms of molecular behaviour
• Sketching and interpreting phase change graphs
• Calculating energy changes involving specific heat capacity and specific latent heat of fusion and vaporization
Guidance:
• Internal energy is taken to be the total intermolecular potential energy + the total random kinetic energy of the molecules
• Phase change graphs may have axes of temperature versus time or temperature versus energy
• The effects of cooling should be understood qualitatively but cooling correction calculations are not required
Data Booklet reference:
Q = mcDT
Q = mL
• The Q represents the heat stored / absorbed / released by a mass m during a process. The c represents the specific heat capacity of the mass, the DT represents the change in temperature (in K or oC). L represents the specific latent heat of the mass. Use the first equation if the temperature changes, use the second equation if the phase changes. The first equation gets its correct sign (+/-) from the DT automatically. The second equation gets its sign (+/-) from the context of the process. Thus, a phase change from solid to liquid would entail a (+) Q, whereas a phase change from a gas to a liquid would entail a (-) Q.
International-mindedness:
• The topic of thermal physics is a good example of the use of international systems of measurement that allow scientists to collaborate effectively
Theory of knowledge:
• Observation through sense perception plays a key role in making measurements. Does sense perception play different roles in different areas of knowledge?
Utilization:
• Pressure gauges, barometers and manometers are a good way to present aspects of this sub-topic
• Higher level students, especially those studying option B, can be shown links to thermodynamics (see Physics topic 9 and option sub-topic B.4)
• Particulate nature of matter (see Chemistry sub-topic 1.3) and measuring energy changes (see Chemistry sub-topic 5.1)
• Water (see Biology sub-topic 2.2)
Aims:
Aim 3: an understanding of thermal concepts is a fundamental aspect of many areas of science
Aim 6: experiments could include (but are not limited to): transfer of energy due to temperature difference; calorimetric investigations; energy involved in phase changes


3.2 – Modelling a gas


Essential idea: The properties of ideal gases allow scientists to make predictions of the behaviour of real gases.
Nature of science:Collaboration: Scientists in the 19th century made valuable progress on the modern theories that form the basis of thermodynamics, making important links with other sciences, especially chemistry. The scientific method was in evidence with contrasting but complementary statements of some laws derived by different scientists. Empirical and theoretical thinking both have their place in science and this is evident in the comparison between the unattainable ideal gas and real gases.
Understandings:
• Pressure Concept
• Equation of state for an ideal gas Concept
• Kinetic model of an ideal gas Gas properties Gas properties 2
• Mole, molar mass and the Avogadro constant The mole Concept, examples
• Differences between real and ideal gases Concept
Applications and skills:
• Solving problems using the equation of state for an ideal gas and gas laws
• Sketching and interpreting changes of state of an ideal gas on pres-sure–volume, pressure–temperature and volume–temperature diagrams
• Investigating at least one gas law experimentally
Guidance:
• Students should be aware of the assumptions that underpin the molecular kinetic theory of ideal gases
• Gas laws are limited to constant volume, constant temperature, constant pressure and the ideal gas law
• Students should understand that a real gas approximates to an ideal gas at conditions of low pressure, moderate temperature and low density
Data Booklet reference:
p = F / A
n = N / NA
pV = nRT
EK = (3/2) kBT / NA = (3/2) (R / NA ) T
• The p represents the pressure a material is subjected to if a force F is applied to it over an area A. The n represents the number of moles contained in N molecules. The NA represents Avagadro's constant, and has a value given by NA = 6.02 x 1023 molecules mol-1. The V represents the volume of a gas, the R represents the ideal gas constant and has a value given by R = 8.31 JK-1mol-1. The T represents the absolute temperature of the gas (in K). The EK represents the mean kinetic energy of the gas molecules. The kB represents the Boltzmann constant whose value is given by kB = 1.38 x 10-23 J K-1. kB and R are related by the equation kB = R / NA.
Theory of knowledge:
• When does modelling of “ideal” situations become “good enough” to count as knowledge?
Utilization:
• Transport of gases in liquid form or at high pressures/densities is common practice across the globe. Behaviour of real gases under extreme conditions needs to be carefully considered in these situations.
• Consideration of thermodynamic processes is essential to many areas of chemistry (see Chemistry sub-topic 1.3)
• Respiration processes (see Biology sub-topic D.6)
Aims:
Aim 3: this is a good topic to make comparisons between empirical and theoretical thinking in science
Aim 6: experiments could include (but are not limited to): verification of gas laws; calculation of the Avogadro constant; virtual investigation of gas law parameters not possible within a school laboratory setting


TOPIC 3 PROBLEM SET

This is the complete problem set for Topic 3 - the same one I hand out. If you lose yours, you can download this one to replace it.



TOPIC 3 FORMATIVE ASSESSMENTS

These are the Formative Assessments (practice) that you will do in order to prepare yourself for the Summative Assessments (evidence of proficiency). You can expect to receive a mark of at least Proficient on the Summative Assessment if you understand everything on these Formative Assessments.



TOPIC 3 PROJECTS

Project marks are meant to replace summative assessment marks. Projects are your last opportunity to demonstrate your proficiency in meeting the standards of the assessment criteria.



EXTENSION NOTES FOR ENRICHMENT