At 190 degreeC. a certain chemical reaction has a rate constant, k, of 2.53 time
ID: 990396 • Letter: A
Question
At 190 degreeC. a certain chemical reaction has a rate constant, k, of 2.53 times 10^-5s^-1,and an activation energy. E_a of 160 kj/mol. Indicate the magnitude of the activation energy on the energy diagram for the reaction below. How does the rate constant change as the temperature is increased? Increases decreases stays the same How does the activation energy change as the temperature is increased? Increases decreases stays the same What experimental data can you plot to determine E_a? (Sketch this plot.)Explanation / Answer
b) As temperature increases rate constant of the reaction increases while activation energy remains the same. The concept for a reaction to happen is that, the collision between those molecules which are associated with a certian minimum amount of energy can lead into a chemical reaction. The minimum amount of energy is called threshold energy. The energy required for a reactant to get threshold energy is called activation energy. In the above diagram, energy of the reactant at normal state is ~ 100 Kj/mol and threshold energy ~ 225KJ/mol. The activation energy is 225-100 = 125 KJ/mol.
When temperature increases, more and more molecules absorb heat energy and reached threshold energy value. Since rate of a reaction increases with increase in concentration of reactant, increase in temperature results increase in rate constant while activation energy remains the same.
To find out activation energy experimentally, you have to find out rate constant for a reaction with two different temperature. From Arrhenius eqn, the activation energy and rate constant are related to each other by,
k= Ae-Ea/RT where k is rate of a reaction at temperature T, A is Arrhenius factor and Ea is activation energy.
Taking log,
log k=- (Ea/2.303RT) + log A
Now plotting log k obtained experimentally wiith the reciporcal of reaction temperature gives a straight line with slope -Ea/2.303R and intercept log A. So from the slope you can find out thevalue of ativation energy Ea.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.