NEET Chemistry Chemical Kinetics Questions Solved

NEET - 2013

What is the activation energy for a reaction if its rate doubles when the temperature is raised from 20°C to 35°C?  (R=8.314 J mol-1 K-1)

(a) 342 kJ mol-1

(b) 269 kJ mol-1

(c) 34.7 kJ mol-1

(d) 15.1 kJ mol-1

(c) Given, initial temperature,
T1=20+273=293K
Final temperature
T2=35+273=308K

R=8.314 J mol-1 K-1

Since, rate becomes double on raising temperature,
∴ r2=2r1 or r2/r1=2

As rate constant, k∝r
∴ k2/k1=2

From Arrnhenius equation, we know that

log k2/k1= -Ea______ [T1-T2/T1T2]
                 2.303R

log 2= -Ea______         [293-308/293x308]
            2.303x8.314

0.3010=   -Ea______         [-15/293x308]
            2.303x8.314

∴ Ea=0.3010x2.303x8.314x293x308
                           15

=34673.48 J mol-1=34.7 kJ mol-1



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