Heat capacity (also known as thermal capacity) is a property that indicates the total amount of heat that can be absorbed or released by a substance or system when its temperature changes. It represents the ability of an object or system to store thermal energy.
This is extensive thermodynamics, which means that its value depends on the amount of matter. In addition, its value depends on other properties such as the mass of the object or system, its chemical composition, its structure and its capacity to store thermal energy.
Definition, What is heat capacity?
The definition of heat capacity can be stated as the amount of heat required to raise the temperature of an object or system by one unit of temperature (usually degrees Celsius or Kelvin).
It is expressed in units of energy per degree Celsius or Kelvin, that is, as joules per degree Celsius (J/°C) or joules per Kelvin (J/K).
Examples of heat capacities
Here is a table showing examples of heat capacities of different materials and substances at constant pressure.
|
Substance |
Heat capacity (J/g°C) |
Description |
|
Water |
4.18 |
Water has a high thermal capacity and is essential for thermal regulation on Earth. |
|
Aluminum |
0.90 |
Aluminum is a lightweight metal commonly used in industrial applications. |
|
Iron |
0.45 |
Iron is a metal frequently used in the manufacture of structures and machinery. |
|
Air |
1.00 |
Dry air is a mixture of different gases present in the atmosphere. |
|
Lead |
0.13 |
Lead is a heavy metal used in various industrial applications and batteries. |
|
Ethanol |
2.44 |
Ethanol is a common alcohol and is used as a fuel and solvent. |
Types of heat capacities
There are several types of heat capacities that are used to describe how the ability of an object or substance to store heat varies under different conditions. The most common types of heat capacities are:
- Heat capacity at constant volume (Cv): It is the heat capacity of an object or substance when the volume is kept constant during the heat transfer process. In this case, there is no work done by the object or substance and all the energy transferred is converted into internal energy changes. Cv is used to describe how the temperature of a system changes at constant volume.
- Heat capacity at constant pressure (Cp): This is the heat capacity of an object or substance when the pressure is kept constant during the heat transfer process. In this case, the object or substance can do work, such as expanding or compressing the system, in addition to absorbing or releasing heat. Cp is used to describe how the temperature of a system changes at constant pressure.
Heat capacity formula
The general formula for calculating the heat capacity (C) of an object or system can be expressed as follows:
C = Q / ΔT
Where:
-
C is the heat capacity.
-
Q is the quantity of heat transferred or absorbed by the object or system.
-
ΔT is the temperature change experienced by the object or system.
It is important to note that the heat capacity may vary depending on whether the process is carried out at constant volume (Cv) or at constant pressure (Cp).
Molar heat capacity formula
In addition, in some cases, the molar heat capacity (Cm) is used, which represents the thermal capacity per mole of substance.
The general formula for molar heat capacity is expressed as follows:
Cm = C / n
Where:
-
Cm is the molar heat capacity.
-
C is the heat capacity.
-
n is the number of moles of substance.
Importance of heat capacity
Heat capacity is a key property in many areas of science and engineering. Below we explore some of its most relevant applications:
Design and optimization of heat transfer systems
Heat capacity is critical in the design of thermal systems such as heat exchangers, boilers and air conditioning systems. In heat exchangers, fluids with high heat capacity are selected to maximize heat transfer efficiency without causing sudden temperature changes.
In the refrigeration industry, gases with specific thermal properties are used to improve the energy efficiency of industrial air conditioning and refrigeration systems.
In power generation processes such as solar thermal and nuclear power plants, the materials used in boilers and pipes must have adequate heat capacity to absorb and transfer large amounts of heat without suffering structural damage.
This also applies to internal combustion engines and cooling systems to prevent overheating of critical components.
Prediction of temperature changes and thermal equilibrium
Heat capacity allows us to predict how the temperature of an object or system will vary when heat is added or removed. For example, in climatology, this property is key to understanding how oceans store and release heat, regulating global climate and smoothing out temperature variations between day and night.
In engineering, it is used to model the thermal behavior of structures and mechanical systems. For example, in the construction of sustainable buildings, materials with high heat capacity are selected to store heat during the day and release it at night, improving energy efficiency. It is also applied in battery design, where temperature control is essential to maintain optimal performance and extend battery life.
Study of heating and cooling processes
In industry and research, understanding how materials and substances are heated or cooled is essential for optimizing thermal processes. In metallurgy, the heat capacity of metals influences their heat treatment processes, such as tempering and annealing, which improve their mechanical properties.
In the food industry, pasteurization and freezing processes depend on precise control of the heating and cooling of products. The heat capacity of the ingredients determines the amount of energy needed to reach safe temperatures without affecting product quality. Similarly, in glass and ceramic production, controlled cooling prevents internal stresses that could cause fractures.
Characterization of material properties
Heat capacity is a key property for the thermal characterization of materials such as metals, liquids, gases, and solids. In materials engineering, it is used to determine which materials are best suited for applications involving exposure to high temperatures or frequent thermal changes.
For example, in the aerospace industry, spacecraft materials must have adequate heat capacity to withstand extreme friction and fluctuating temperatures during re-entry into the atmosphere. In electronics, materials with low heat capacity are chosen for heat sinks, allowing efficient heat transfer away from sensitive circuits.
Study of chemical reactions
In chemistry, heat capacity is essential for calculating the amount of heat absorbed or released during a reaction. In calorimetry, it is used to measure the enthalpy of chemical reactions, which helps to understand their feasibility and safety.
For example, in the pharmaceutical industry, the thermal stability of compounds is crucial to ensure the efficacy of drugs during storage and transport. In the production of fuels and explosives, the heat capacity of materials is studied to predict how they will react to changes in temperature and to avoid risks of ignition or explosion.