Question

question 8 (1 point)
consider the following reaction mechanism. changing the concentration of which substance(s) would have
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
d
d and e
question 9 (1 point)
which statement about the factors that affect reaction rates is false?
decreasing the concentrations of the reacting particles decreases the chance of collision.
a collision with poor orientation requires a higher activation energy than a collision with optimum
orientation.
increasing the pressure in a gaseous reaction increases the chance of collision.
a reaction occurs every time particles of the reactants collide.
increasing the temperature increases the reaction rate.
question 10 (1 point)

Explanation:

Question 8

In a reaction mechanism, the rate - determining step (slow step) governs the overall reaction rate. The rate law for the slow step \(2A
ightarrow B + 2C\) is \(Rate=k[A]^2\). Substances \(B\), \(C\), \(D\) are involved in fast steps. Changes in their concentrations do not significantly affect the overall rate as the slow step is the bottleneck. Only the concentration of \(A\) (reactant in the slow step) has a major impact on the rate of the overall reaction.

• For the statement "Decreasing the concentrations of the reacting particles decreases the chance of collision": According to the collision theory, the rate of a reaction is proportional to the number of collisions. Fewer particles (lower concentration) mean fewer collisions.
• For the statement "A collision with poor orientation requires a higher activation energy than a collision with optimum orientation": Activation energy is the minimum energy required for a reaction. A poorly - oriented collision may need more energy to overcome the energy barrier (activation energy) compared to an optimally - oriented collision.
• For the statement "Increasing the pressure in a gaseous reaction increases the chance of collision": For gaseous reactions, \(PV = nRT\). At constant \(T\) and \(V\), increasing \(P\) (by adding more gas molecules) increases \(n\) (number of moles). More gas molecules in the same volume mean more collisions.
• For the statement "A reaction occurs every time particles of the reactants collide": For a reaction to occur, particles must collide with sufficient energy (greater than or equal to the activation energy) and with proper orientation. Not all collisions meet these criteria.
• For the statement "Increasing the temperature increases the reaction rate": According to the Arrhenius equation \(k = A e^{-\frac{E_a}{RT}}\), increasing \(T\) increases the rate constant \(k\). Higher \(k\) means a higher reaction rate as \(Rate=k[reactants]^n\).

Answer:

A

Question 9