Che 341 Chemical Reaction Engineering

Gazi University September, 2008

Department of Chemical Engineering

Che 341 Chemical Reaction Engineering

2008-2009 Fall Semester

Homework-1

1) How much does a reaction rate with an activation energy of 14,700 cal/mole vary when the temperature is increased from 320 to 345 K?

2) Given that the first-order rate constant for the overall decomposition of N2O5 is

k=(4.3x1013 s-1) e-103 000/RT

calculate the time required for 90% reaction at 50 0C. The activation energy is in J mol-1.

3) Although the thermal decomposition of ethyl bromide is complex, the overall rate is first order, and the rate constant is given by the expression k = (3.8x1014 s-1) e -229 000/RT, where the activation energy is in J mol-1. Estimate the temperature at which the decomposition is 70% complete in 1 h.

4) A certain reaction has a rate given by ;

-rA= 0.005 CA2, mol/ cm³.min

If the concentration is to be expressed in mol/L and time in hours, calculate the rate constant in the units of moles, L and hour?

5) Milk is pasteurized if it is heated to 55 °C for 40 min., but if it is heated to 80 °C it needs 10 s for the same result. Find the activation energy (Ea) of this process?

6) The rate constant of a first order reaction is 4.60x10-4 s-1 at 350 °C. If the activation energy (Ea) is 104 kJ/mol , calculate the temperature at which its rate constant is 8.80x10-4 s-1 ?

7) Variation of the rate constant with temperature for the first order reaction :

2 N2O5 (g)2 N2O4 (g) + O2 (g)

is given in the following table. Determine graphically the activation energy for the reaction.

T(K) / k (s-1)
273 / 7.87x103
298 / 3.46x105
318 / 4.98x106
338 / 4.8707

8) Suppose that a substance X decomposes into A and B in parallel paths with rate constants given by

kA = (1015 s-1) e-126 000/RT kB = (1013 s-1) e-83 700/RT

where the activation energies are given in J mol-1. At what temperature will the two products be formed at the same rate?