What is Chemical Reaction?

- A process that leads to the chemical transformation of one set of chemical substances to another. Chemical reaction stoichiometry expresses the quantitative relationship between reactants and products in a chemical equation.

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What is Stochiometry?

– Theory of proportions in which chemical species combine with one another. 

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Stoichiometric eqt of chemical reaction:

- Statement of the relative number of molecules or moles of reactants and products that participate in the reaction.

- 2SO2 + O2 --->2SO3

 

Stoichiometric ratio:

- ratio of species stoichiometry coefficients in the balanced reaction equation 

-can be used as a conversion factor to calculate the amount of particular reactant (or product) that was consumed (produced).

 

Example the reaction of nitrogen and hydrogen to produce ammonia:

N2 + 3H2 → 2NH3

The stoichiometric ratios:

N2/H2 = 1/3 

N2/NH3  = 1/2

H2/NH3 = 3/2

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What is Limiting Reactant?

-The reactant in a chemical reaction that limits the amount of product that can be formed.

-The reaction will stop when all of the limiting reactant is consumed

What is Excess Reactant?

-The reactant in a chemical reaction that remains when a reaction stops when the limiting reactant is completely consumed.

What is Fractional Conversion?

-Number of moles of a compound that reacted divided by the amount of the moles that were fed.

What is Extent of Reaction?

-A quantity that measures the extent in which the reaction proceeds. It is usually denoted by the Greek letter ξ.

What is Combustion Process?

-A chemical process in which a substance reacts rapidly with oxygen and gives off heat.

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Example of Elemental Balance

 

Methane reacts with chlorine to produce methyl chloride and hydrogen chloride:

CH4 + Cl2 = CH3Cl + HCl

 

Once formed, the CH3Cl may undergo further chlorination to form methylene chloride, chloroform, and carbon tetrachloride:

 

CH3Cl + Cl2 = CH2Cl2 + HCl

CH2Cl2 + Cl2 = CHCl3 + HCl

CHCl3 + Cl2 = CCl4 + HCl

 

In a methyl chloride production process, methane and chlorine are fed to a reactor in a mole ratio of 5:1. (The ratio is kept high to minimize polysubstitution.) A single-pass conversion of 100% may be assumed. The mole ratio of CH3Cl to CH2Cl2 in the product is 4:1, and negligible amounts of CHCl3 and CCl4 are produced. The product gases are cooled, condensing the CH3Cl and CH2Cl2, which are then separated in a distillation column. The gas leaving the condenser goes to a scrubber in which the HCl is absorbed. The gas leaving the scrubber, which may be considered pure methane, is recycled back to the reactor.

 

For a production rate of 1000 kg CH3Cl/hr, calculate:

 

(a) The flow rate and molar composition of the fresh feed.

(b) The rate at which HCl must be removed in the scrubber.

(c) The molar flow rate of the recycle stream.

 

 

SOLUTION:

Basis: 1000 kg of CH3Cl produced = 19.8 kg mol

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1. Balance around condenser and still

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2. Element balances around the block

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3. Balance at recycle mixing point

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4. Answer the questions

 

(a) Flow rate = (n1 + n2)/hr = (24.8 + 29.8) kmol/hr = 54.6 kmol/hr 

xCH4 = 24.8/54.6 = 0.454

(b) 29.9 kgmol/hr

(c) 124.2 kgmol/hr

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TRY OUT THIS QUESTION:

 

In the Deacon process for the manufacturing of Chlorine, HCl and O2 react to form Cl2 and H2O. Sufficient air is fed to provide 35% excess oxygen and the fractional of conversion of HCl is 85%. Calculate the mole fractions of the product stream components.

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