There are many things that we know about thermal properties of solids, liquids and gases. The knowledge gained over a period of time is incredible. Once understood, these concepts form the foundation of thermal insulation, heat transfer, mechanical and electrical conductivity and thermal conductivity. These are 2 technical terms that need to be understood very carefully before delving into the thermal properties of solids, liquids and gases. They are heat, temperature and pressure.
Heat energy or heat gained is the amount of heat that has been absorbed or lost. Temperature is a kind of measurement that helps in measuring the level of coolness or warmth present of an object or a body at a particular point in time. It is measured in Celsius and is usually referred to as Specific Heat Capacity. Specific heat capacity describes the rate at which heat is lost or gained. A higher number of conduction cycles per unit area of space means a lower rate of heat energy loss and hence it is often referred to as a low thermal conductivity.
Specific heat capacity is influenced by the fluid’s porosity, density, and porosity index. The rate of thermal expansion is related to the thermal conductivity of a fluid. The law of thermal expansion tells us that the rate of thermal expansion is directly proportional to the surface tension of a fluid. This thermal expansion is a function of the specific heat capacity of a fluid.
The other term that is used in thermal properties of matter is enthalpy. It refers to the thermal energy dissipation as a result of evaporation. The enthalpy of a fluid is directly proportional to the area of its volume. Thus the smaller the volume, the greater the enthalpy. The thermal properties of matter can be studied using the relative humidity, the vapor pressure, and the vapor density at various temperatures.
The second term is the thermal conductivity of a fluid. It is an inverse function of the density of a liquid and is related to the thermal contact pressure between one body and another. It is usually found in solids such as water, but in certain cases in gases like argon. It defines the thermal conductivity of a fluid at a specific temperature and can be defined as the amount of heat produced or absorbed by a solid or a gas at that temperature.
In case of solids, one can find equilibrium at low temperatures. At high temperatures the equilibrium is broken, because the thermal conductivity decreases with increasing temperature. In this case, the solids become so thin that heat energy is no longer required to move them around. This results in an imbalance at high temperatures and leads to a drop in the solubility of the solid. In this case, a different kind of solid is required to substitute the dissolved solids. If the equilibrium is broken, the equilibrium is disturbed and a change in thermal conductivity of the system is noticed.
At very low temperatures, the equilibrium is often not so easy to establish. To understand what happens at critical temperatures, we have to study the processes that take place at critical temperatures in gases. At critical temperatures, there is the splitting of gas molecules into two or more molecules. This splitting of molecules leads to loss of thermal energy through spontaneous combustion. If the temperatures are high enough, the atoms of gas become unbalanced and it leads to the generation of heat.
The thermal properties of matter study can also be done on solidifying media. When a solidifying agent is heated to a specific temperature, it forms either colloidal ice or foam. Although both these media are in three states, the thermal properties of matter state that the ice is in liquid state, while the colloidal ice is in solid form.