# Matter

- molecular kinetic theory
- ideal gases; pV = NkT
- absolute zero
- relationship between temperature and average molecular kinetic energy
- internal energy
- energy required for temperature change = mcΔθ

For most classes, the equation linking a thermal store of energy to the temperature change is a good place to start. This will be familiar from their GCSE specification, if for no other reason than the fact it is one of the only equations they cannot rearrange using the 'triangle method'. Although not required, comparing this with the equations for latent heat reminds students of the fact that heat supplied can cause two kinds of change in a substance. This then allows you to gauge their understanding off the subtleties of molecular arrangements in various states of matter. Those who study chemistry will probably have a lot to offer in discussions here.

The size of your class will determine how many of the practicals can be done by students, perhaps in a circus, and which you demonstrate yourself. This is a great opportunity for data analysis and best fit lines which do not go through the origin - until the numbers lead to the concept of an actual, meaningful or 'absolute' zero. The individual relationships - each of which can be predicted by discussion and thought experiment - can be combined to give the ideal gas equation. At this point many pupils will appreciate some practice with problems requiring them to simplify from this to a straightforward relationship before solving numerically (different specifications may require different levels of recall for the derivation).

Past exam specifications and questions have often asked students to be clear about the assumptions and limitations of the ideal gas model. In fact, students are often surprised by just how good the results of the equations are when they realize what we must ignore.

The expressions for internal energy and how this relates to particles can be challenging for many students to visualise. In particular it is worth spending a little time on the relevance of the 'root mean square' speed. Those students studying a statistics module in maths can often make good suggestions for this.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

## Links and Resources

### Specific Thermal Capacity of Aluminium

Many colleagues will be familiar with the equipment and method for measuring aluminium's specific heat capacity. Even if students have completed this at GCSE, it's probably worth revisiting as a class practical to remind them of the measurement needed and the challenges, particularly that of heat loss to the environment.

Having two sets of apparatus running simultaneously, one heating a kilogram of water rather than aluminium, makes a dramatic point about heat capacity.

The IoP guidance on specific heat capacity intended specifically for A level classes provides more detailed suggestions about approaches and accopmanying calculations.

### An Old Principle Saves Energy

The matched teacher guidance and student worksheet here are very useful to help structure some mathematical practice. Covering both specific and latent heat, the context of a condensing boiler ensures students recognise the social relevance in terms of cost. You may find that following this up with relevant past paper questions will ensure students become more confident with their mathematical reasoning.

### Episode 601: Brownian Motion and Ideal Gases

Where better, this resource suggests, than with the experiment that Einstein used to show the characteristic properties of molecules in a gas? From the movement of smoke particles the practical suggestions and discussion points lead to the behaviour of 'ideal' gases. There is a lot of guidance for teachers that prompts reflection on what we hope students to remember and why.

### Boyle's Law

The detailed guidance from Practical Physics gives safety advice as well as a teaching structure for this apparatus. Students are able to collect data which can then be plotted, exactly as Robert Boyle did, to show a clear relationship between pressure and volume. It can be useful to remind students to include columns in their table for derived as well as measured data.

### Nuffield Advanced Science: Book of Data (Second Edition)

Many departments will have a stack of these data books around. Despite many values being available online, it is often more useful to supply standard values for calculations to ensure conformity within a class (the existence of varied 'constants' online is of course an interesting discussion in its own right). For gas law calculations, it may be particularly useful to issue page 154 of the PDF to pupils.

### From the Pressure Law to the Kelvin Scale

This guidance from Practical Physics emphasizes the analysis of data rather than the hands-on method. You may find it a useful structure to guide students through their own 'discovery' of absolute zero, and parts of it offer something close to a script. Although not something it makes explicit, the approach described would also be a great prompt to discuss reliability of the data and how we measure this, ie uncertainty.

### Gas Properties

This is a topic where simulations such as this one from PhET are invaluable. Once students are comfortable with the kinetic theory model they can reason out the gas laws in a narrative way, which is supported by a model where they can change one variable at a time.

Wherever possible, it's best to think of these simulations as illustrations, rather than demonstrations. We should always remember to reinforce with students that these models are based on empirical, real-world data - often with the removal of inconvenient complications!

### Episode 603: Kinetic Model of an Ideal Gas

This detailed resource emphasizes the many linked concepts that students must understand in this topic. Example demonstrations and class practicals are given, as are suggestions about effective ways to make links between microscopic factors (motion of particles) and macroscopic observable effects (such as temperature and pressure). The many consequences of variable energy within the particles of a substance, from evaporation below the nominal boiling point to the mechanism of cooling by evaporation.

### Kinetic Theory: the Tennis Ball and Electric Current

The first part of the student activity sheet describes a sample testing procedure - dropping tennis balls - and the data collected about the changes to the gas inside. Students are challenged to use their knowledge of the gas laws to explain the patterns of the data supplied.

The second part might be best saved for more able students, or given as optional extension work. It encourages students to extend the model of freely moving particles in a gas to electrons within a metal. The value of applying a familiar model to a new situation is clear, but it risks confusing weaker candidates who struggle to see the link between two apparently disparate areas of physics.

The teacher's notes include model answers and suggestions of useful analogies.

Subject(s) | Science |
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Tags | n.a |

Age | 16-19 |

Last updated | 12 July 2016 |

Rating | |

URL | https://www.stem.org.uk/lxpbo |