Use the collision theory of gas-phase reactions to calculate the theoretical value of the second-order rate constant for the elementary reaction \(\mathrm{H}_{2}+\mathrm{I}_{2} \rightarrow \mathrm{HI}+\mathrm{HI}\) at 650 K. The collision cross-section is \(0.36 \mathrm{\ nm}^{2}\) , the reduced mass is \(3.32 \times 10^{-27} \mathrm{\ kg}\), and the activation energy is \(171 \mathrm{\ kJ} \mathrm{\ mol}^{-1}\) . (Assume a steric factor of 1.)

Text Transcription:

H_2+I_2 rightarrow HI+HI

0.36 nm^2

3.32 times 10^-27 kg

171 kJ mol^-1

Chapter 14 First Law of Thermodynamics: energy cannot be created or destroyed - Chemical Reaction: system (the reaction itself) & surroundings (beaker, solvent, etc.) Spontaneous Processes: a process that DOES occur under a speciﬁc set of conditions without ongoing outside intervention. - ex: combustion of methane Nonspontaneous Process: a process that does NOT occur under a speciﬁc set of conditions Entropy: Qualitative - Entropy (S): a measure of how dispersed the system’s energy is. By removing the barrier the energy that was contained becomes dispersed throughout the container [Figure 14.1] - Boltzman: S = (k) ln(W) k: the Boltzman Constant = 1.33 X 10 -23J/K W: the number of possible arrangements - The larger the number of possible arrangements the larger the entropy - The smaller the number of possible arrangements the smaller the entropy - The most probable state is the one with the largest number of possible arrangements Entropy on a Microscopic Scale Molecules exhibit several types of motion: - Translational: movement of the entire molecule from one place to another - Rotational: rotation of the molecule about on its axis or sigma bonds - Vibrational : periodic motion of atoms within a molecule. Entropy Change in a System: ∆Ssys Entropy Change: ∆Ssys = Sﬁnal - Sinitial Isothermal Processes: S = absolute entropy of a substance at 1 atm.