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Phases of Matter, Phase Transitions, Latent vs Sensible Heat, Phase Diagrams

← Builds on Heat Capacity, Specific Heat, Calorimetry (Q=mc-delta-T)

Terms you will need

  • solidA solid is a state of matter that keeps its shape and volume, and is hard to change without breaking.
  • liquidA liquid is a state of matter that keeps its volume but can change shape to fit the container it is in.
  • gasA gas is a state of matter that can change both its shape and volume, and spreads out to fill any container it is in.
  • meltingMelting is when a solid turns into a liquid because it gets warmer.
  • freezingFreezing is when a liquid turns into a solid because it gets colder.
  • boilingBoiling is when a liquid turns into a gas because it gets very hot.

How this topic runs

  1. 1Start here
  2. 2How it works
  3. 3At competition depth

Phases of matter describe the different forms in which a substance can exist, such as solid, liquid, or gas, based on its physical state. Phase transitions occur when a substance changes from one phase to another, such as melting or boiling. These transitions involve changes in the arrangement and energy of the particles within the substance. Latent heat refers to the energy absorbed or released during a phase transition without a change in temperature, while sensible heat refers to the energy that causes a temperature change within a phase. Phase diagrams are graphical representations that show the conditions of temperature and pressure under which different phases of a substance exist and coexist in equilibrium. Understanding these concepts is essential for explaining how substances behave under various conditions and for predicting the outcomes of physical processes involving changes in state.

Figures (7)

Figure 1.12 The phase diagram (pT graph) for water shows solid (s), liquid (l), and vapor (v) phases. At temperatures and pressure above those of the critical point, there is no distinction between liquid and vapor. Note that the axes are nonlinear and the graph is not to scale. This graph is simplified—it omits several exotic phases of ice at higher pressures. The phase diagram of water is unusual because the melting-point curve has a negative slope, showing that you can melt ice by increasing the pressure.
Figure 1.13 Direct transitions between solid and vapor are common, sometimes useful, and even beautiful. (a) Dry ice sublimes directly to carbon dioxide gas. The visible “smoke” consists of water droplets that condensed in the air cooled by the dry ice. (b) Frost forms patterns on a very cold window, an example of a solid formed directly from a vapor. (credit a: modification of work by Windell Oskay; credit b: modification of work by Liz West)
Figure 1.14 Equilibrium between liquid and gas at two different boiling points inside a closed container. (a) The rates of boiling and condensation are equal at this combination of temperature and pressure, so the liquid and gas phases are in equilibrium. (b) At a higher temperature, the boiling rate is faster, that is, the rate at which molecules leave the liquid and enter the gas is faster. This increases the number of molecules in the gas, which increases the gas pressure, which in turn increases the rate at which gas molecules condense and enter the liquid. The pressure stops increasing when it reaches the point where the boiling rate and the condensation rate are equal. The gas and liquid are in equilibrium again at this higher temperature and pressure.
Figure 1.15 Temperature versus heat. The system is constructed so that no vapor evaporates while ice warms to become liquid water, and so that, when vaporization occurs, the vapor remains in the system. The long stretches of constant temperatures at 0°C0°C and 100°C100°C reflect the large amounts of heat needed to cause melting and vaporization, respectively.
Figure 1.16 Condensation forms on this glass of iced tea because the temperature of the nearby air is reduced. The air cannot hold as much water as it did at room temperature, so water condenses. Energy is released when the water condenses, speeding the melting of the ice in the glass. (credit: Jenny Downing)
Figure 1.17 The ice on these trees released large amounts of energy when it froze, helping to prevent the temperature of the trees from dropping below 0°C0°C. Water is intentionally sprayed on orchards to help prevent hard frosts. (credit: Hermann Hammer)
Figure 1.18 (a) Energy is required to partially overcome the attractive forces (modeled as springs) between molecules in a solid to form a liquid. That same energy must be removed from the liquid for freezing to take place. (b) Molecules become separated by large distances when going from liquid to vapor, requiring significant energy to completely overcome molecular attraction. The same energy must be removed from the vapor for condensation to take place.

Phases of matter are distinct forms a substance can take, like solid, liquid, or gas, based on how its particles are arranged and move. These changes involve energy shifts that rearrange the particles. Latent heat is the energy used during a phase change without changing the temperature, while sensible heat is energy that changes the temperature within a single phase.

Phase diagrams are charts showing how temperature and pressure affect which phases of a substance exist and where they can coexist. They help predict how a substance will behave under different conditions. Understanding these ideas helps explain how materials respond to changes in their environment and how to control those changes in experiments or real-world situations.

Key Points

  • A solid is a phase that resists deformation and maintains a fixed shape under applied shear stress.
  • A liquid is a fluid with a relatively high density that is insensitive to changes in temperature and pressure.
  • A gas is a fluid with a relatively low density that is sensitive to changes in temperature and pressure.
  • Melting is an equilibrium phase transition from solid to liquid at a specific temperature and pressure where the phases coexist.
  • Freezing is an equilibrium phase transition from liquid to solid at a specific temperature and pressure where the phases coexist.

Terms

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