Heat Capacity and Specific Heat

Heat is energy that is transferred from one body to another as a consequence of a temperature difference. When two bodies at different temperatures come into contact, energy is transferred (i.e., heat flows) from the hotter to the colder. The result of this energy transfer is typically, but not always, an increase in the temperature of the colder body and a decrease in the temperature of the hotter body. A material can absorb heat without increasing its temperature by transitioning from one physical state (or phase) to another, such as from solid to liquid (melting), solid to vapor (sublimation), liquid to vapor (boiling), or solid form to another (usually called a crystalline transition). During the 18th and 19th centuries, the important distinction between heat and temperature (heat is a type of energy and temperature being a measure of how much of that energy is present in a body) was clarified. Since all forms of energy, including heat, can be converted into work, energy is measured in units of work such as joules, foot-pounds, kilowatt-hours, or calories. There are exact relationships between the amounts of heat added to or removed from a body and the magnitude of the effects on the body’s state. The calorie and the British thermal unit are the two most commonly used heat units (BTU).

Overview

The amount of energy required to raise a unit mass of a substance through a specified temperature interval is referred to as the heat capacity or specific heat of that substance. The amount of energy required to raise a body’s temperature by one degree varies depending on the constraints imposed. When heat is applied to a gas that is confined at constant volume, the amount of heat required to cause a one-degree temperature rise is less than when the same gas is allowed to expand (as in a cylinder fitted with a movable piston) and thus do work.

As in the first case, all of the energy is used to raise the temperature of the gas, whereas in the second case, the energy not only contributes to the temperature increase of the gas but also provides the energy required for the gas’s work on the piston. As a result, the specific heat of a substance is affected by these conditions. The specific heats that are most commonly determined are the specific heat at constant volume and the specific heat at constant pressure.

It is difficult to relate to heat in a body because heat is limited to energy transfer. Heat is not stored energy in the body (nor is it work, as work is also energy in transit). However, it is customary to distinguish between sensible and latent heat. The amount of energy required to convert a liquid to a vapor at constant temperature and pressure is referred to as latent heat. The heat of fusion is the energy required to convert a solid to a liquid, and the heat of sublimation is the energy required to convert a solid directly to a vapor, both of which occur under constant temperature and pressure conditions.

Air is a mixture of gases and water vapor, and the water in the air can change phase, becoming either liquid (rain) or solid (snow). The concept of sensible heat was introduced to distinguish between the energy associated with phase change (the latent heat) and the energy required for a temperature change. The sensible heat in a mixture of water vapor and the air is the energy required to produce a specific temperature change, excluding any energy required for a phase change.

Heat

Heat is described in thermodynamics as energy transferred to or from a thermodynamic system via mechanisms other than thermodynamic work or matter transfer. The following section of this article discusses the various energy transfer mechanisms that define heat.

Heat transfer, like thermodynamic work, is a process involving multiple systems and not a property of any single system. In thermodynamics, heat energy transfers contribute to changes in the system’s cardinal energy variable of states, such as internal energy or enthalpy. This is distinct from the common understanding of heat as a property of an isolated system.

Heat Capacity

We can say that heat is a type of energy that is also known as thermal energy. Energy can be converted from one form to another (for example, a blender converts electrical energy to mechanical energy), but it cannot be created or destroyed; rather, energy is conserved. In basic thermodynamics, the higher a material’s temperature, the more thermal energy it possesses. Furthermore, at a given temperature, the more of a given substance there is, the more total thermal energy the material has.

Over an atomic level, absorbed heat causes the atoms of a solid to vibrate, as if they were connected by springs. The energy of the vibrations increases as the temperature rises. This is the only motion possible in metal. Absorbing heat in a liquid or gas causes the atoms in the molecule to vibrate, causing the molecule to rotate and move from one location to another. Because liquids and gases have more “storage” possibilities for energy, their heat capacities are greater than those of metals.

Specific Heat of a Substance

Specific heat values can be calculated as follows: If two materials, each at a different temperature, come into contact with one another, heat always flows from the warmer material into the colder one until both of them reach the same temperature. As per the law of conservation of energy, the heat gained by the initially colder material must equal the heat lost by the initially warmer material.

We realize that when a substance absorbs heat energy, its temperature rises. The temperature rise for each substance differs when the same amount of heat is applied to equal masses of different substances. This is because different substances have different heat capacities. Thus, the heat capacity of a substance is the amount of heat required to raise the temperature of the entire substance by one degree. Whenever a material has a single mass, the heat capacity is referred to as the specific heat capacity or the specific heat.

Q=CmΔt

Here,

Q is said to be the quantity of heat absorbed by a body

M is said to be the mass of the body

Δt is said to be the rise in temperature

C is said to be the specific heat capacity of a substance depending on the nature of the material of the substance.

We could indeed explain why water has a high specific heat by referring to hydrogen bonds. The molecules must vibrate in order to raise the temperature of the water due to the multitude of joined hydrogen bonds. Because there are so many hydrogen bonds, it takes more energy to break the water molecules by vibrating them.

Correspondingly, it takes some time for hot water to cool down. The temperature drops as heat are dissipated, and the vibrational movement of water molecules slows. The heat emitted compensates for the cooling effect of heat loss from liquid water.

Specific Heat of Metal

Specific heat is defined as the amount of heat energy required per unit mass to raise the temperature by one degree Celsius.

Specific heat capacity cannot be calculated using data such as atomic number, atomic weight, density, magnetic susceptibility, Vicker’s hardness, and so on. To calculate specific heat capacity, data from an experiment in which heat is exchanged between a metal sample and another object while the temperature is monitored is required.

A sample of metal is heated to a known temperature and placed in a known mass of water at a known initial temperature to determine its specific heat. The metal will lose energy to the water and thus cool, whereas the water will gain energy and thus warm. The system’s final temperature will be reached when a uniform temperature is reached throughout the system. The heat generated by water equals the heat lost by metal.

Also read: Important Topic of Chemistry: Critical temperature

FAQs

Why is the specific heat capacity of water higher than metal?

It is due to the specific heat efficiency of the metal spoon being much lower than that of the soup liquid. Water possesses the highest specific heat capacity of any liquid.

What is the difference between heat capacity and specific heat capacity?

The specific heat capacity of a substance is the amount of heat required to raise its temperature by one degree Celsius. Correspondingly, heat capacity is defined as the ratio of energy provided to a substance to the corresponding increase in temperature.

What is the primary benefit of water's heat capacity?

Since water has a high heat capacity, increasing the temperature by one degree necessitates a greater expenditure of energy. The sun emits a relatively constant level of energy, which heats up sand and water more quickly.