What Is Hybrid Heat?

The heat of mixing refers to the heat absorbed or released when different substances are mixed under constant temperature and constant pressure. When mixing an ideal gas, no mixing heat is generated. The heat of mixing of low-pressure gas is small and negligible. Some liquids with similar structures (such as toluene and benzene) also have a small heat of mixing. For high-pressure gases and liquids with very different structures, the heat of mixing must be considered. The mixing process is sometimes similar to the reaction process, and it is difficult to strictly distinguish between the two. For example, the mixing heat of aqueous hydrochloric acid solution and sodium hydroxide aqueous solution is actually the reaction heat of hydrogen ions and hydroxide ionization to synthesize water. ^[1]

Heat of mixing, the thermal effect produced when many different substances are mixed with each other to form a homogeneous system. Normally this mixing process is performed at a constant temperature and pressure. Common heat of mixing includes the heat of mixing between different gases or liquids, the heat of dissolution, and the heat of dilution. For several specified substances, the heat of mixing depends on the temperature, pressure, and amount of each substance. Generally, the heat of mixing refers to the thermal effect when several substances are mixed into a 1mol / L solution (that is, n ₁ + n ₂ + ...... = 1 mol) at a certain temperature and pressure. The mixed heat can be measured directly with a calorimeter. The mixing heat of low-pressure gas is small, the mixing heat of high-pressure gas is large; the mixing heat of liquid, molecular structure and similar size is small, and the mixing heat of large difference in molecular structure and size is large. The magnitude of the mixing heat can provide useful information on the changes in intermolecular interactions before and after mixing, the presence of solutes and solvents in the solution, and their interactions. Therefore, the determination of mixed heat is one of the important methods for solution research.

Thermal effects of two or more gases or liquids mixing to form a homogeneous system. The factors affecting the heat of mixing include temperature, pressure, properties of solutes and solvents and their relative contents, and volume changes during mixing. Generally, the heat of mixing refers to the thermal effect of mixing several substances at a certain temperature and pressure to form a molar solution at a certain ratio, and the unit is coke / mole. If a binary solution formed from two liquid components is considered, it is assumed that n _i , _Hi and Mi are the number of moles of component i, the molar enthalpy of pure component i, and the partial molar enthalpy of component i in solution ₁ + n ₂ + = 1), the molar heat of mixing is:

When two or more substances are mixed to make a solution, the heat change accompanying the production of a solution equivalent to 1 mol is referred to as the heat of mixing. Mixing heat can be used directly

The heat of mixing is of great significance in the study of solution theory. The sign and size of the mixing heat H ^M reflects the existence state of the solute and the solvent in the solution and their interactions. It is also one of the important basis for testing various empirical rules and solution theories. Generally, the heat effect is small when the gas is mixed under low pressure, and the heat of mixing is high under high pressure. For organic liquids, substances with similar molecular structures and similar sizes have a small thermal effect when mixed; organic compounds with significantly different molecular structures and sizes have a larger mixing heat. As for the electrolyte solution, if the two neutral salt solutions are mixed without chemical reaction, the thermal effect is also small; if there is precipitation or hardly ionized substances generated during mixing, the thermal effect is greater. ^[2]