3.2
3.2.1
What a state we are in
Introduction
In this unit we consider the different physical forms that a substance may take and how they may be graphically represented in terms of properties.
Some properties are very familiar, such as temperature and pressure. Later in this course we will introduce some other less common, but very useful thermodynamic properties, such as enthalpy and entropy.
Terms
Be able toBy the end of this section you should be familiar with terms such as:
Phase, Pure Substance
Extensive, Intensive and Independent Properties
Equilibrium
Identify some common Properties For a known mass, convert between Extensive and Intensive Properties
3.2.2
What a state we are in
What are weather fronts?
What are weather fronts?
How often do you look at the weather forecast ? Whilst the forecast often seems incorrect, modern computer simulation has become increasingly more accurate.
An understanding of the variation in pressure and temperature in the atmosphere is critical for predicting future developments.
Have a look at this video, the terms ‘pressure’ and ‘temperature’ are commonly used, but what actually do they mean ?
3.2.3
What a state we are in
Pause for thought
Warm Air
Cold Air
In the video James Chubb introduced weather fronts. The weather over the UK depends upon the temperature and humidity of the approaching air masses and we can detect these changes as pressure changes with a barometer.
But, have you ever thought, is one temperature and one pressure unique?
Are there different sorts of air that can have the same temperature and pressure?
3.2.4
What a state we are in
Screencast
Outline
In this unit we will consider the different physical forms that a substance may take and how they may be represented in terms of properties.
We will start by defining the phase of a substance. This will allow us to define a homogenous mixture which will then help us to introduce the concept of pure and simple substances. Followed by the introduction of thermodynamic properties and the state of a substance allowing us to explore the idea that the state depends upon thermodynamic properties.
3.2.5
What a state we are in
Review Questions
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Referring to the material presented in this section, can you answer the following questions -
A mixture of oxygen and hydrogen at atmospheric temperature and pressure is placed in a closed container. Do you think this should be described as
(a) a pure substance (b) a homogenous substance (c) a simple substance?
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Referring to the material presented in this section, can you answer the following questions -
What is the difference between an Extensive and an Intensive property?
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Referring to the material presented in this section, can you answer the following questions -
Which of the following are extensive properties?
(a) temperature (b) volume (c) density (d) energy
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Referring to the material presented in this section, can you answer the following questions -
Which of the following are intensive properties?
(a) specific volume (b) pressure (c) melting point (d) momentum
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Referring to the material presented in this section, can you answer the following questions -
How many properties are required to define the state of a simple compressible system?
