Question

Percy prepares vegetable curry (liquid) in a pressure cooker. If the raw potatoes are P, the raw tomatoes are T, the raw onions are O, and the cooked meal is M, then 2P + T + O → 3M may represent the cooking process. Sometime during the process, Manu opens the lid and checks the curry to find that the potatoes are half-cooked (take XP = 0.5). Volume of the cooker is 5L and CPo = CTo = COo = 1.5. What can you say about the composition in the cooker at the instant of time when the lid is opened, if initial temperature was 310K?

(a) XT = 0.35

(b) CO = 1.125

(c) T = 380K

(d) CM = 2.5

The question was posed to me in an internship interview.

My enquiry is from Introduction to Reactor Design in section Homogenous Reactions in Ideal Reactors of Chemical Reaction Engineering

Answer 1

Right option is (b) CO = 1.125

Best explanation: If we assume the pressure cooker to be a batch reactor, P, T, O as the reactants and M as the product, we can use material balance to get

XT = CAo*b*XA/(a*CBo)

CO = CAo*(1-0.5*XA)

CM = CAo*(3*XA)

It is a liquid reaction so change in volume can be ignored. Thus we cannot say anything about the temperature based on the given information.