Physics
Changes of state
Changes of state refer to the physical transformations that matter undergoes when transitioning between solid, liquid, and gas states. These changes occur due to variations in temperature and pressure. For example, when a solid ice cube melts into liquid water, it undergoes a change of state from solid to liquid due to an increase in temperature.
Written by Perlego with AI-assistance
6 Key excerpts on "Changes of state"
Learn about this page
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
8Solids & Liquids
Relationship to Bonding
The properties of substances are directly impacted by their bonding forces, both intramolecular and intermolecular. This is an important point to consider as you investigate the states of matter. Greater amounts of attraction mean more resistance to change from the current state of matter. Also, if the particles in a substance are extremely attracted to one another, they will be more likely to be found in the solid or liquid state than in the gaseous state.Phase Changes
• Phase changes are caused by changes in temperature or pressure.• The solid state is least energetic, exhibits only vibrational motion, and the particles are closest together. See Figure 8.2 .Figure 8.2. Proximity of Particles in Different Phases• The liquid state exhibits higher energy than solids, exhibit vibrational and translational motion, and the particles are spread further apart. See Figure 8.2 .• Gases have the greatest amount of kinetic energy compared to other states, have translational, vibrational, and rotational motion, and contain particles whose distance between the particles is much larger than the particles themselves. See Figure 8.2 .• Phase changes involve a change in enthalpy (ΔH) that is unique for each substance and each transformation. A positive enthalpy (ΔH > 0) means that energy must be put into the system, whereas a negative enthalpy (ΔH < 0) means that energy must be released or removed from the system. See Table 8.1 .Table 8.1. Energy Involved with Phase ChangesTEST TIPWhen providing explanations involving states of matter, frame your answer from a kinetic molecular standpoint: How fast are the molecules moving, what kind of motion do they have, and how close are the particles to one another?Heating and Cooling Curves
• A heating curve is a graph that shows what happens to a substance when heat is added at a constant rate. A heating curve will have an overall positive slope. See Figure 8.3
eBook - ePubThe Really Useful Science Book
A Framework of Knowledge for Primary Teachers
- Steve Farrow, Amy Strachan(Authors)
- 2017(Publication Date)
- Routledge(Publisher)
As has already been described, the states of matter can be visualized in terms of the vibration of their constituent atoms or molecules, and Changes of state in substances are brought about by the transfer, into and out of the substances, of heat energy in the form of atomic or molecular motion (see Key Idea 3.1 : The states of matter; and Changes of state). Increases in motion, and therefore increases in the amount of thermal energy transferred into substances, give rise to: • changes in state via melting, boiling and evaporation; • the expansion of heated substances; • the burning of fuels and the cellular respiration of carbohydrates in living cells. All of these processes are described in Key Idea 3.3 : Heating and cooling everyday materials; Changing materials; Chemical reactions and heat energy; and Changes involving oxygen. The difference between heat and temperature Heat is the total amount of thermal energy contained in a given amount of material and is measured in joules. Temperature is a measure of the intensity of heat – of how hot something is – and is measured in degrees Celsius (°C). On the Celsius scale, 0° is the freezing point, and 100° is the boiling point, of pure water. Some examples might make the distinction clearer: • Two litres of water at 20°C will hold twice as much heat as 1 litre of water at 20°C. Although the water is at the same temperature in each case, there will be twice as many molecular collisions in 2 litres of water as in 1 litre (because there are twice as many molecules) – the total quantity of heat in 2 litres of water will therefore be double that which is present in 1 litre. • There will be more heat in a bath full of tepid water than there will be in a match flame
eBook - ePubBiomolecular Thermodynamics
From Theory to Application
- Douglas Barrick(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
Chapter 7 , will use this dissection to analyze chemical reactions and chemical equilibrium. Here, we analyze simple systems where a single chemical component can partition reversibly into different types of bulk materials with distinct properties.Phases and Their TransformationsWhen materials have large-scale differences in their bonding patterns, they are considered to be different phases. These atomic-level differences in bonding produce discernably different mechanical and thermal properties on the macroscopic scale. These include differences in densities, compressibilities, viscosities, and heat capacities, as well as electromagnetic and optical properties such as polarizabilities and refractive indices.Perhaps the most dramatic (and most familiar) phase transitions are among the three common forms of matter: solid, liquid, and gas. For pure, single-component systems, changes among these three phases involve change in noncovalent interactions, but not covalent bonding. Differences in physical properties among the phases give rise to obvious differences in how different phases distribute in a container: gas phases expand to fill the entire container, liquid phases collect in the bottom but flow to conform to the container’s shape, and solid phases (also at the bottom) are rigid, retaining their shape rather than that of the container. The six transitions among these three basic phases are given in Figure 6.1 .Figure 6.1 Phase transitions between solid, liquid, and gas for a single-component system. Transitions are labeled s for sublimation , d for deposition , c for condensation, v for vaporization , m for melting (sometimes referred to as fusion ), and f for freezing . The gas phase has a much larger molar volume (inverse density) than the other two phases. Typically, solid has the lowest molar volume (highest density), although for water, the solid phase has a higher molar volume.¶
eBook - ePubProgression in Primary Science
A Guide to the Nature and Practice of Science in Key Stages 1 and 2
- Martin Hollins, Maggie Williams, Virginia Whitby(Authors)
- 2013(Publication Date)
- David Fulton Publishers(Publisher)
All materials are made from minute particles called atoms, and these can join together in small or large groups to form molecules. Under the normal range of temperatures these molecules are constantly vibrating rapidly. It is the way in which they are arranged and how close together they are that will determine whether a material is a solid, a liquid or a gas.- There are only minute gaps between the molecules in solids. The molecules are held rigidly together (or bonded) and they vibrate about a fixed point.
- The gaps between the molecules in liquids are further apart and this allows the molecules to slide over one another so that the material can flow.
- The gaps between the molecules in gases are even further apart allowing them to move freely.
This form of movement is a manifestation of the kinetic energy — the energy that moving things have — of the atoms. The amount of energy will determine whether the substance exists in a solid, a liquid or a gas state. If the energy is increased sufficiently in a solid (for example when chocolate is heated), then the bonds between the molecules break down and the particles can move more freely in all directions. The solid becomes a liquid. If the amount of energy is decreased, then the liquid will become solid.Particular points to note are:- atoms are the building blocks of life;
- many substances can exist in a solid, liquid or gas form;
- something is still the same substance, even if it has changed from one state to another.
Children's understanding of solids, liquids and gases
Research carried out by the Primary SPACE team (Science Process and Concept Exploration 1991) indicates that children at both Key Stages 1 and 2 have a much clearer understanding of the solidness of a substance and the liquidness of a substance than they do of the nature of a gaseous substance.Most young children do not think of gases as being materials at all. They associate the existence of air only with moving air, although they understand that air enables us to live. However, they believe that 'gas' is dangerous. It is therefore not surprising that when asked 'What is in the other half of a glass that is half-filled with orange juice?', almost all children will answer 'Nothing. For almost all of the gases that children will have had experience of, even if they have been unaware of it, will have been invisible. Most of those gases which are coloured are also poisonous.
eBook - ePub- Kevin R. Reel(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
vapor pressure curve defines the boundary between the liquid and gas phases on the phase diagram. The vapor-pressure curve determines the partial pressure of gas that can be in the vapor phase at any given temperature.PHASE CHANGES
• Phase changes are caused by changes in pressure or temperature. • Phase change involves a change in enthalpy (ΔH) that is unique for each substance and each change.Change of phase Name of change ΔH for change Solid to liquid Melting (fusion) ΔH > 0 Liquid to solid Freezing ΔH < 0 Liquid to gas Vaporization ΔH > 0 Gas to liquid Condensation ΔH < 0 Solid to gas Sublimation ΔH > 0 Gas to solid Deposition ΔH < 0 • A heating curve is a temperature-versus-time graph when heat is added at a constant rate, or a temperature-versus-heat-added graph. A heating curve in reverse is called a cooling curve . Two procedures are used to calculate the heat added or subtracted in a heating or cooling curve:1. Heat required to change state is calculated by multiplying the change in enthalpy for the change (such as melting or freezing) by the amount of material.2. Heat required to increase the temperature of the material in one phase, or state, is calculated by multiplying the amount of material, by the change in temperature, and the specific heat of the material.Example: Calculate the total amount of heat needed to raise 20.0 g of frozen water at −10°C to steam at 115°C. The following information will be useful:
eBook - ePub- Gino C. Segrè, John D. Stack(Authors)
- 2022(Publication Date)
- University of Chicago Press(Publisher)
Eq. (3.1) is quite general, requiring only that each term in the equation is well defined. The process may involve equilibrium or nonequilibrium states, and the equation is independent of the particular variables needed to specify internal energy, heat, and work. In the next section, for processes connecting thermodynamic equilibrium states, it is shown how to write the equation in terms of differential changes in thermodynamic variables.3.2 State Variables. EntropyThe equilibrium state of a thermodynamic system is defined by the values of a small number of macroscopic variables. For a gas containing a single type of molecule, the relevant variables are pressure, volume, temperature, and the number of molecules in the system. Any three of these are enough to specify the thermodynamic state of the system, the fourth being specified by the equation of state. State variables are independent of the history of the system and are either extensive or intensive. Extensive variables, like volume and number of particles, are “how much” variables. Intensive variables like pressure and temperature, are “how strong” variables.Neither work nor heat is a state variable. Both are physical quantities whose values depend on the history of the system. Taking a system through a closed cycle of thermodynamic states, a net amount of work may be done, and heat absorbed or given off. But the system could equally well have been left in its initial state, and not taken through a cycle. In that case, the net work done and heat absorbed are zero, so the work done and the heat absorbed obviously depend on the history of the system, not just its present state.The work done by a gaseous system in going from state 1 to state 2 is given byThe value of W1→ 2depends on the particular path taken through thermodynamic states in going from state 1 to state 2. For an infinitesimal change, dW = PdV
