From EIT Chemical Review, Second Edition
Overview
ACCOUNTING PRINCIPLE: This can be expressed by the equation:
Q E - Q B = ? Q I - ? Q O + ?Q P
where
| Q | = | physical quantity chosen for accounting |
| Q E | = | the quantity at end of accounting period |
| Q B | = | the quantity at the beginning of the accounting period |
| Q I | = | the quantity which enters the system during accounting period |
| Q O | = | the quantity which leaves the system during accounting period |
| Q P | = | Quantity created or destroyed during accounting period |
In ordinary processes involving chemical (not nuclear) reactions, ?Q P = 0 If the quantity in the system does not change with time , Q E - Q B = 0 and the accounting equation reduces to ?Q I - ?Q O = 0. In this case, input equals output. The system is said to be under steady state condition. The accounting principle can also be used to make an energy balance for a system. In carrying out mass and energy balances, several definitions and relations about different properties of substances are useful. These are:
Density of a substance, ? = mass/volume and Specific gravity of a substance, s = ?/ ? r
where ?r is the density of the reference substance. For liquids and solids, water is usually the reference substance at 4 C( ? = 1000...
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