# Short Questions in Chemical Engineering

Question

1. Since radioactive decay is a first-order process, the decay rate for a particular nuclide is commonly given as the half-life. Given that potassium contains 0.0118% 40K, which has a half life of 1.27×109 years, how many disintegrations per second are there in a gram of KCl?

2. The decomposition of HI to H2 + I2 at 508°C has a half-life of 135 min when the initial pressure of HI is 0.1 atm and 13.5 min when the pressure is 1 atm. (A) Show that this proves that the reaction is second order. (B) What is the value of the rate constant in L mol-1s-1? (C) What is the value of the rate constant in bar-1s-1? (D) What is the value of the rate constant in cm3s-1?

3. The reaction between propionaldehyde and hydrocyanic acid has been studied at 25°C. In a certain aqueous solution at 25°C the concentrations at various times were as follows:

t/min                                   2.78       5.33       8.17
[HCN]/molL-1                     0.0990    0.0906    0.0830
[C3H7CHO]/molL-1             0.0566    0.0482    0.0406

t/min                                 15.13      19.80       ∞
[HCN]/molL-1                     0.0706    0.0653    0.0424
[C3H7CHO]/molL-1             0.0282    0.0229    0.0000

What is the order of the reaction, and what is the value of the rate constant k?

4. The rate constant for the reaction is

I + I +Ar → I2 + Ar

Is 0.59 ×1016cm6mol-2s-1 at 293K. What is the half-life of I if [I]0  = 2×10-5molL-1 and [Ar] = 5×10-3molL-1?

Summary

These questions belong to Chemical Engineering and they deal with radioactive decay of KCl, decomposition of HI to hydrogen and iodine, reaction between propionaldehyde and hydrocyanic acid and iodine and argon reaction and iodine half life.

Note: The solution is in handwritten format.

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