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Conservation of Matter ad Energy

In an isolated system the algebraic sum of all the forms of matter quantities is found to be invariable and constant. It was Lavoisier who is believed to have found and agree to measurement of materials during and after experiments while others before him focussed mainly on the observation and descriptions of the chemical changes during experiments.

When carefully measured all the substances involved in reaction Lavoisier found that matter is neither created nor destroyed during a chemical reaction. It might change from one form to another but these could always be accounted and measured for. 

We like all other people in scientific community still use the principle almost on a daily basis and the law is ideally called conservation of matter.

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Conservation of Matter and Energy Definition

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Whenever energy of a particular form disappears an exactly equivalent amount of another form must be produced and this works out similarly for matter as well where the matter of a particular entity changes its form but the overall matter within the system remains exactly same.

The total matter of a reacting system is conserved. The law is valid for all processes and whenever there is a reaction between atomic nuclei, the change in corresponding mass of the matter of one substance is always accompanied with the system energy change, but the matter within the system appears in some other form and hence both matter and energy is conserved.

$2H_{2} + O_{2} \rightarrow 2H_{2}O$

In the above reaction we could clearly see that the number of hydrogen atoms and oxygen on both side of the reaction are same. The form of their existence might be different but the matter remains same on both sides.

The atomic mass of hydrogen is 1g and to that of oxygen atom is 16 g.

One the reactant side hydrogen total mass is 2 x (2 *1) = 4 g

Oxygen total mass on reactant side is 2 x 16 = 32 g

Total mass on reactant side is (Hydrogen) 4 + (Oxygen) 32 = 36 g

On the product side we have similar mass number of 4 g of hydrogen + 32 g of oxygen making it 36 g in all.

The Law of Conservation of Matter

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The law of conservation of matter is universal and is applied all over and across all processes. During early 18th century many scientists noticed that there is hardly any change in mass when they carried out a chemical reaction except when they did these in open.

In adiabatic condition, or conditions where neither heat nor matter is exchanged with the surroundings, the chemical reactants undergoing changes in their chemical characteristics including physical state do not lose the overall matter.

The number of particles which goes into the reaction remains exactly same even after the reaction is over. Substances might combine together (reactants) in a chemical change and form new substances or products but the total mass of these substances remains same. As there is no change in mass number on either side of any of these substances we say mass is conserved.

The physical states of the substances might differ on either side of the reaction but the matter or mass remains same of each individual reactants.

2 Cu (s) + $O_{2}(g) \rightarrow$ 2 CuO(s)

In the above reaction, copper reacts with oxygen from atmosphere to form copper oxide. Now the physical state of copper is solid while that of oxygen is gaseous but the final product is again solid and gaseous oxygen combines with solid copper to form copper oxide. Although it clearly shows, that physical state of one of the reactant is different but the mass number remains same on either side.

Two atoms of copper having atomic mass of 63.5 g (total 127 g) combines with one oxygen molecule (mass 32 g) to form two moles of copper oxide weighing 159 g.

Explain Law of Conservation of Matter

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When we explain law of conservation of matter, we need to understand the importance of a adiabatic system where no matter is allowed to escape out of the system for better understanding of the law of conservation of matter.

If we allow the reacting system to allow the matter to escape then it will be difficult to prove the law experimentally. For example if during experiment a gas escapes from system then as per the law mass will definitely be conserved as nothing goes out of the Earth system and the gaseous particle will definitely be combining somewhere else and maintain the conservation but the immediate experiment will not be perfect.
  • The subject is very demonstrative as the idea of both constancy and change goes hand in hand. The big idea is about the concept that matter cannot be created or can be destroyed by ordinary changes. 
  • The idea also highlights that all matter is made up of very small particles or atoms and these matters may combine or recombine to change form but the total amount of these particles remain same even after the chemical change.
  • We could observe that matter exists as solids, liquids and gas or plasma and that these are made up of atoms. However the atoms combine or interact with each other or rearrange themselves, the overall number of atoms remains the same.
  • In a closed system, no matter how the reacting molecules combine chemically or physically the mass always remain same and hence the matter contained inside also remains unchanged. Nothing is allowed in or out of the system.

Law of Conservation of Matter Example

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Law of conservation of matter is nothing but the conservation of mass on either side of the reaction. It has to be taken into account that the law could be ascertained only in an isolated system where the mass could be measured both before and after the chemical reaction.

Let us take an example of decomposition of sodium carbonate. The sodium carbonate will decompose into sodium oxide and carbon di oxide. The mass of sodium carbonate before decomposition was found to be 106 g. The combined mass of both carbon di oxide and sodium oxide on product side is found to be 106 g.

$Na_{2} CO_{3} \rightarrow Na_{2}O + CO_{2}$

Reactant side: 2 x 23 + (12 + 3 x 16) = 46 + 60 = 106 grams

Product side: (2 x 23 + 16) + (12 + 32) = 62 + 44 = 106 grams

Reactant side = product side

Law of conservation of matter or mass experimentally proved.
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