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Mass and Energy balance

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Rural Technology

We can conduct audit of mass and energy. Let’s study following examples:

1) When wood is burned in air–

100gm of wood when burned in air, it produces 2g. of ash. Where did the balance of 98 g. go? If you carry out detailed investigation, you may find some gas and vapour goes into air. In the above example, we found 143.79g. of Carbon dioxide (CO2) and 58.9g of water vapour gets generated in the process. The material balance is written as follows: 100 gm wood ® 2 gm (ash) + 143.79 gm (CO2) + 58.8 g (water) i.e total 204.5g. 100 gm wood ® 204.5 g of above materials It is quite clear that 104.5g other material gets added in the burning process from outside. The other material is nothing but oxygen (O2) gas.

2) To measure water contain in the substance.

For measuring water content in any substance, first measure total mass of the substance, and then dry it, completely. After drying, take the weight again. The difference between the weight is the weight of water that has gone off. Intext Questions 7.1 Fill in the blanks: i) When a chapatti weighing 70g was put in the pan and roasted, the weight became 60g. The water vapour removed is ____ g. ii) E = m ´ _____

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