Question

question 7 (1 point)
which quantity does not increase when the temperature of a reaction system is raised?
activation energy
number of collisions
number of effective collisions
average kinetic energy of the particles
all of the above increase
question 8 (1 point)
consider the following reaction mechanism. changing the concentration of which substance(s) would hav
the most effect on the rate of the overall reaction?
2a ---> b + 2c (slow)
b + c ---> d + e (fast)
c + d ---> e + f (fast)
a
a and c
b

Explanation:

Question 7

• Activation energy: It is a property of the reaction itself (determined by the nature of reactant molecules and the reaction pathway). It does not change with temperature.
• Number of collisions: As temperature increases, particle - motion speeds up. According to the kinetic - molecular theory, the number of collisions between particles increases.
• Number of effective collisions: With higher temperature, more particles have energy greater than or equal to the activation energy. So, the fraction of effective collisions (collisions that lead to a reaction) increases.
• Average kinetic energy of the particles: The average kinetic energy of gas particles is given by \(E_{k}=\frac{3}{2}kT\) (where \(k\) is the Boltzmann constant and \(T\) is the temperature in Kelvin). For other states (liquids and solids), as temperature increases, the vibrational/translational/rotational kinetic energies of particles increase on average.

In a reaction mechanism, the rate - determining step (the slow step) governs the rate of the overall reaction. The rate law for the slow step \(2A
ightarrow B + 2C\) is \(rate = k[A]^{2}\) (assuming elementary reaction, and for an elementary reaction, the rate law can be written from the stoichiometry). Substances \(B\), \(C\), \(D\), and \(E\) are involved in fast steps. Changing their concentrations will not affect the rate of the overall reaction as the slow step is the bottleneck. Only the concentration of \(A\) (the reactant in the rate - determining step) will have a significant effect on the rate of the overall reaction.

Answer:

activation energy

Question 8