Gazi University
Department of Chemical Engineering
Che 341 Chemical Reaction Engineering
2008-2009 Fall Semester
September, 2008
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 N 2O5 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 = (3.8x10 14 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?