FAQs on Properties of Pure Substance, Thermodynamics - Mechanical Engineering
|1. What is a pure substance in thermodynamics?
A pure substance in thermodynamics refers to a material that has a uniform and definite chemical composition throughout. It can exist in different phases, such as solid, liquid, or gas, and can undergo phase changes without any change in its chemical composition. Examples of pure substances include water, oxygen, and carbon dioxide.
|2. What are the properties of a pure substance?
The properties of a pure substance are classified into two categories: intensive and extensive properties. Intensive properties are independent of the size or quantity of the substance and include temperature, pressure, density, and specific heat capacity. Extensive properties, on the other hand, depend on the size or quantity of the substance and include mass, volume, and internal energy.
|3. How are phase changes of a pure substance described in thermodynamics?
Phase changes of a pure substance are described using phase diagrams, which show the relationship between temperature, pressure, and the phases of the substance. The phase diagram typically consists of regions corresponding to different phases, such as solid, liquid, and gas, and lines representing phase boundaries. These phase changes occur at specific temperatures and pressures known as melting point, boiling point, and critical point.
|4. What is the significance of the critical point in thermodynamics of pure substances?
The critical point is the highest temperature and pressure at which a pure substance can exist as a liquid and gas simultaneously. At the critical point, the properties of the gas and liquid phases become indistinguishable, and the substance exhibits unique characteristics. For example, the density becomes equal to the critical density, and the distinction between the gas and liquid phases disappears. Understanding the critical point is essential for various industrial processes like liquefaction of gases and supercritical fluid extraction.
|5. How are the thermodynamic properties of a pure substance determined using equations of state?
Equations of state, such as the ideal gas law or the van der Waals equation, are used to determine the thermodynamic properties of a pure substance. These equations relate the properties of a substance, such as pressure, temperature, and volume, to each other. By manipulating the equations and considering appropriate assumptions, one can calculate properties like specific volume, specific enthalpy, and specific entropy. These equations provide a mathematical representation of the behavior of pure substances and are crucial for thermodynamic analysis and calculations.