Specific Heat, Heat Capacity, First Law of Thermodynamics & Internal Energy Explained in Details.

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First Law of thermodynamics-

The first law of thermodynamics is a version of the law of conservation of energy (The total energy of an isolated system is constant; energy can be transformed from one form to another, but neither can it be created nor it can be destroyed.)

The change in an internal energy in the system is equal to the heat added to the system minus the work done by the system.

(Change in Internal Energy) ΔU = (Heat added TO the system) Q – (Work done BY the system) W.

To understand specific heat in details first we should understand about Internal Energy and how to measure it.

The first law makes use of concepts like Internal Energy, Heat and System Work.

Internal Energy- (ΔU)

·       Internal energy is the molecular activity of a substance – the vibrational, translational, and rotational kinetic energy of the molecules of the substance. You can imagine that this would be difficult to measure, but fortunately this energy results in something that we can easily measure: a change in the temperature of the substance.

·       The internal energy of a system can be changed by transfers of matter or heat or by doing work.

·       Internal energy is a state property i.e. its value depends only upon the state of the substance but does not depend upon how that state is achieved.

Ex- When oil is reacted with oxygen, potential energy is released, since new chemical bonds are formed in the products which are more powerful than those in the oil and oxygen. The energy resulting from this process may be converted directly to electricity (as in a fuel cell), or into thermal energy (if the oil is simply burned).

ΔU = nCVΔT

Heat-

·       Heat may be defined as energy in transit.

·       When two systems at different temperatures are kept in contact with each other then after some time temperatures of both the systems become equal and this phenomenon can be described by saying that energy has flown from one system to another.

·       This flow of energy from one system to another on account of temperature difference is called heat transfer.

System Work

When work is done by a thermodynamics system, it is generally done by gas. The work done by gas at constant pressure is, W= P Δ V.

Specific Heat-

The amount of heat per unit mass required to raise the temperature by one degree Celsius.

What is specific heat of water?

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance. As a result, water plays a very important role in temperature regulation.

 What is heat capacity (Thermal Capacity)?

·       It is a measurable physical quantity equal to the ratio of the heat added to (or removed from) an object to the resulting temperature change.

·       The unit of heat capacity is joule per kelvin {\displaystyle \mathrm {\tfrac {J}{K}} }(J/K) or kilogram metre squared per kelvin second squared Kgm² / Ks².

·       The dimensional form is L²MT⁻²Θ⁻¹.