Themochemistry science , Types of systems and law of conservation of energy


Energy is very important in our life , where we can’t carry out different activities ( mental or muscular ) without the produced energy from burning sugar inside our bodies , we can’t cook our food without the heat energy produced from the burning of natural gas .

There are various forms of energy like Chemical energy , Heat energy , Light energy , Electrical energy and Kinetic energy .

In spite of this classification of energy into different forms , There is a relationship between all of these forms , as the energy is converted from one form to another , this leads us to the law of conservation of energy .

Law of conservation of energy

The energy in any physical or chemical change can be neither created nor destroyed , but it is transformed from one form to another .

Types of systems

Types of systems

Themochemistry science

All the chemical reactions and the physical changes are accompanied by changes in the energy , Thermochemistry is a branch of thermodynamics which concerned with these changes .

Thermochemistry is the science that concerns with the heat changes that accompanying the chemical changes ( the reactions ) and the physical changes .

Thermodynamics is the science that deals with the study of energy and how it transfers .

The dissolving of ammonium nitrate salt in water represents a physical change , The combination of hydrogen and oxygen to form water represents a chemical change ( reaction ) .

Before studying of how we can calculate the heat changes accompanying the chemical and physical change , we have to know the following basic concepts : System and surrounding , First law of thermodynamics , Temperature and heat , Specific heat .

System and surrounding

System is the part of the universe chosen for study in which the physical or the chemical change occurs , Surrounding is the part outside the system that exchanges the energy with the system in the form of heat or work .

The chemical reactions are accompanied with changes in the energy ( releasing or absorbing ) , this energy exchange occurs between the reaction mixture and its surrounding , where :

The system expresses the reactants and the products .

The system boundary expresses the wall of container ( a flask or a test tube ) in which the reaction occurs .

The surrounding expresses the medium surrounding the reaction container ( the laboratory ) .

Types of systems

Systems are classified according to their ability to exchange the energy or matter with its surrounding into Open system , Closed system and Isolated system .

Open system is the system that freely exchanges matter and energy with its surrounding .

Closed system is the system that exchanges energy ( but not matter ) with its surrounding in the form of heat or work .

Isolated system is the system that exchanges neither energy nor matter with its surrounding , The system doesn’t interact with its surrounding .

The medical thermometer is considered as a closed system because it allows the exchange of energy only with the surrounding in the form of heat .

First law of Thermodynamics

Any change in the system’s energy Δ E system is accompanied by a change in the surrounding energy Δ E surrounding by a similar value , but with an opposite sign to make the total energy remain constant .

Δ E system = − Δ E surrounding

First law of thermodynamics includes the study of the energy exchange between the isolated system and its surrounding .

First law of thermodynamics : The total energy of an isolated system is constant even the system is changed from one state to another .

Heat and temperature

You can read this article about Combustion ( bomb ) Calorimeter , Specific heat and calculation of the quantity of heat

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