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CBSE Class 9 Answered

How can you say law of conservation of mass is true if humans and other living organisims are being created or destroyed?
Asked by vilasinip34 | 08 Mar, 2018, 07:44: PM
answered-by-expert Expert Answer
conservation principle is applicable for isolated system. we can not apply this coservation principle to open system.
We are dealing conservation of mass mostly in fluid dynamics, chemical reactions. In fluid dynamics we have a flow system consisting of some pipes and other flow sytem components like nozzle, diffuser etc. every flow system has some inlet and outlet. In order to get the flow variables like velocity, pressure and temperature we apply the principle of conservation of mass. we are given with how much fluid enters the inlet, so we know mass input. We account this mass at various inlets and outlets of flow system components and we get flow system variables.  This is worked out till the outlet of the overall system and made sure that the mass enters the inlet leaves the outlet. This what we mean isolated system.
 
In chemical reaction, we are given the total mass of reactants and we are sure the total mass of products will be same.
so this conservation of mass we apply only on the given reactants and created products. In nuclear reeactrion there is a mass difference between reactrants and products, but we know this mass difference is converted into energy. Though mass is conserved before and after chemical reaction, the energy is released/absorbed due to internal energies of reactant and producct.
 
But if we consider water in open ponds and lakes, we can not estimate the water content at any given time, becasue some quantity may evaporate, some quantity will be taken away and some quantoty will be added from other sources. This is open system.
What you refer the creation and destruction of human being, animals and plants are open system. we do not look for conservation of mass in this open system.
Answered by Thiyagarajan K | 09 Mar, 2018, 08:22: AM

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