Balance it out.

Chemistry Level 2

Consider the following steady-state open system, involving flow of three substances A,B \text{A,B} and C \text{C} :

Two streams 1 1 and 2 2 , of mass flow rates m ˙ 1 \dot{m}_1 and m ˙ 2 \dot{m}_2 respectively enter the first chamber. m ˙ 1 \dot{m}_1 has a variable mass flow rate of m ˙ 1 ( t ) = ( 2 t + 3 ) kg/s \dot{m}_1(t)=(2t+3)\text{kg/s} where t t is time in seconds. Two other streams 3 3 and 4 4 , of mass flow rates m ˙ 3 \dot{m}_3 and m ˙ 4 \dot{m}_4 respectively exit it. These two streams which exit the first chamber also enter a second chamber, a reaction chamber. In this chamber, A,B \text{A,B} and C \text{C} react to form another substance D \text{D} through the reaction equation 4 A + 2 B + C D 4\text{A}+2\text{B}+\text{C}\rightarrow \text{D} . All excess reactants are ejected through another stream going out of the reaction chamber. Calculate the mass flow rate of D \text{D} after 2.5 2.5 seconds, in kg/min \text{kg/min} .

Additional information :

  • Stream 1 1 is 70 % 70\% A \text{A} and the rest C \text{C} .
  • Stream 2 2 is 60 % 60\% B \text{B} and the rest A \text{A} .
  • Stream 3 3 is 20 % 20\% C \text{C} and also outputs equivalent amounts of A \text{A} and B \text{B} .
  • Stream 4 4 comprises of only A \text{A} .
  • Assume that A,B \text{A,B} and C \text{C} all have the same molar mass.


The answer is 924.

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1 solution

Saya Suka
Apr 16, 2021

m1 = m2 & m3 = 3 × m4

There should be 55% of A, 30% of B and 15% of C in the reaction chamber. A would be wholly utilized and left 3.75% (B+C mixture) as excess reactants.

m1(2.5) = 2 × 2.5 + 3 = 8 kg/s
Total mass of inputs
= m1 + m2
= 8 + 8
= 16 kg/s


Answer
= (100% – 3.75%) × 16 kg/s
= [ 15.4 kg/s ] × 60s
= 924 kg/minute

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