Phase Equilibrium: A Look at its Heating Applications

Phase equilibrium sounds complex (almost science fiction-like) and it can be tricky. However, it simply refers to “the study of the equilibrium which exists between or within different states of matter,” such as gasses, liquids, and solids. 

This study isn’t as abstract as it seems and is used for various industrial purposes, especially ones with specific heating requirements. This post will examine phase equilibrium, real-world applications, and the heating implications associated with this study. 

What is phase equilibrium?

This is a topic in chemistry referring to the equilibrium found between different states of matter: solid, liquid, and gas. Equilibrium means there’s no change taking place in the chemical potential of different components, where there’s a uniform interaction happening between phases.

The phase rule governs phase equilibrium processes. This rule has to do with how variables, such as temperature, pressure, and volume, are imposed on a certain phase. It’s these factors that will determine phase transition, like the melting or boiling point of a substance. Where phase equilibrium is concerned, a particle that phases into another won’t result in an energy loss.

Types of equilibrium 

Phase equilibrium

An example of phase equilibrium would be water molecules at 0° Celsius which is both the freezing point and melting point for water. In this phase, the number of water molecules turning to ice is the same as the number of molecules melting. This creates an equilibrium between solid and liquid.

Ice (s) ⇌ Water (l)

Phase equilibrium also applies to a liquid in a closed container. The number of liquid molecules turning into vapor will be the same number of vapor molecules turning into liquid. The rate at which the liquid evaporates is equal to condensation.

Water (l) ⇌ Water (g)

Solute-solid equilibrium

This type of equilibrium appears when a solute in a saturated solution is in contact with an undissolved solute. If the number of molecules depositing out of the solution is equal to the molecules dissolving, there’s solute-solid equilibrium. 

Solute (aq) ⇌ Solute (s)

Gas-liquid equilibrium

In a closed container, like a soft drink, there can be an equilibrium between the gas in the liquid and the gas filling the remainder of the container. Carbon dioxide gas in the soft drink is in equilibrium with the gas filling the empty space.

Gas (solution) ⇌ Gas (g)

Real-world applications for phase equilibrium

Lime production

To create a forward reaction, lime production must be endothermic. That means 178 kilojoules of heat energy are absorbed for each mole of calcium oxide being formed. If one mole of gas is formed in this reaction, there will be a net increase in lime production since there aren’t gaseous products. In a ventilated lime kiln, the pressure can also be decreased to increase the formation of gas molecules which means more carbon dioxide or lime is formed. 

Ammonia synthesis

Haber process

The Haber process of ammonia synthesis uses the reaction between nitrogen gas and hydrogen gas. This requires the use of air, higher hydrocarbons, and water.

Bosch-Haber process

The Bosch-Haber process of ammonia synthesis considers this to be an exothermic reaction since it gives off heat. This process requires four moles of the reactant gas to produce two moles of the product gas which is a decrease in the number of gas molecules. 

Phase equilibrium rules are used to find a way to yield the most ammonia. Higher temperatures will produce less ammonia but will work faster than with low temperatures.

Sulfuric acid production

To produce sulfuric acid, sulfur dioxide is mixed with air with a catalyst of vanadium oxide at high temperatures. This oxidizes the sulfur dioxide, making it an exothermic reaction. 

This results in sulfur trioxide, a precursor to sulfuric acid. The sulfur trioxide will then be dissolved in concentrated sulfuric acid to form oleum (fuming sulfuric acid). Then, once water is added, sulfuric acid is produced.

Methanol production

To make methanol, carbon monoxide, and hydrogen gases are synthesized. A high temperature and high pressure are used in a catalyst to produce the best amount of yield. Methanol provides additional resources for plastics, car parts, construction materials, and paints. It’s a clean energy source for fueling vehicles, boilers, and cookstoves.

Heating implications

A change in pressure, concentration, or temperature impacts the results of phase equilibrium reactions so a small offset can create a new equilibrium. In terms of heating implications in industrial settings, adding, removing, or changing the heat will shift the equilibrium and produce either different chemicals or different amounts.

Chemical equations for reactions typically don’t include a heat value, however, reactions generally include an absorption or release of heat. It’s up to industrial heaters to achieve sustainable temperatures to reach ideal states.

Wattco heating recommendations

At Wattco, we have various types of heaters to apply to different projects in industrial settings. Wattco manufactures a complete line of flange heaters, circulation heaters, tubular heaters, and immersion heating elements for a wide variety of industrial and commercial applications. 

With a resourceful sales team and knowledge base, Wattco provides customers with heaters and controls with exceptional performance and reliability, making Wattco the one-stop for all heating product needs. Contact us for a quote today.