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Unformatted text preview: Mole Balances Chap. 1 The rate law i s an a l ~ e b r a ~ quation. ec -r4 k,C, =- I + klCA The convention For a given reaction. the particufar co-xentrarion dependence that the rate l aw follows (i.e.. - r, = kc, o r - r A = kc; or ... ) must be determined from experirnenral observation. Equation ( 1-2) states that the rate of disappearance o f A i h equal to a rate constant k ( which is a f unction o f temperature) times the square of the concentration of A. B y convention. r , is the rare of formation of A ; consequently. -- is t he rate u f disappearance of A. Throughout this book. the ,, phrase mte qf gerlerution means exact1y the same as the phrase rntr qf'jiwmntion, and these phrases are used interchangeably. 1.2 The General Mole Balance Equation
To perform a mole balance on a ny system, the system boundaries must first be specified. The volume enclosed by these boundaries is referred to as the sTstern v o l ~ m e We shall perform a mole balance on species j i n a system volume. . where species j represents the particular chemical species of inrerest, such ax water or NaOH (Figure 1-3).
System Vorurne Figure 1-3 B alance on system volume. equation: 1 1-1
Rate of flow ofjinto the system (moles1time A mole balance on species j at any instant i n time. t. yields the following R ate of generation ofeaction hemical r j by c within the system (molesJtime) - = Rate o f f low ofjoutof]+ the system (molesftime) I
- o f j w irhin the system 1
( 1-3) Mole balance In + Out + Generation = Accumulation 50 a Fi + G, 3
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