Reaction Rate Test

True/False

Increasing the concentration of a reactant always results in an increase in the reaction rate.
Increasing the temperature of a reaction always increases the rate of reaction.
Reactions often occur in a series of steps called a "mechanism."
The rate of a reaction depends on the rate of the slowest step in its mechanism.
Increasing the temperature of a reaction 10 ^oC can double the rate of a reaction because the particles collide twice as frequently at the higher temperature.
The activated complex is a low-energy, stable molecule that is formed as an intermediate step in a chemical reaction.
The activation energy is the energy needed to form the activated complex from the reactants.
Increasing the temperatuare of a reaction speeds up a reaction by lowering the activation energy.
A catalyst speeds up a reaction by lowering the activation energy.
A catalyzed reaction follows the same mechanism as an uncatalyzed reaction.

Multiple Choice (Choose the best answer.)

Which of the following is not a correct interpretation of the collision theory of chemical reactions?
The rate depends on the number of chemical bonds broken in a reaction.
The rate depends on the number of successful collisions in a given time.
The rate depends on the kinetic energy of the colliding particles.
The rate depends on the surface area of the reactants.
The rate depends on the mass of the reacting molecules.
Reaction rates are affected by concentration, collision geometry, and the presence of a catalyst. Which one of the following statements is FALSE?
Larger concentrations of reacting particles increases the number of collisions.
Molecules that do not collide in the correct orientation lower the reaction rate.
The slowest step in the mechanism determines the rate.
A catalyst increases the speeds of the reacting particles.
A catalyst lowers the activation energy of a reaction.

Use the potential energy diagram below to answer questions 3 - 7.
What is the potential energy of the products?
150
200
250
350
450
What is the activation energy of the reaction?
150
200
250
350
450
What is the potential energy of the activated complex?
150
200
250
350
450
What is the heat of reaction?
150
200
250
350
450
The reaction is:
catalyzed.
uncatalyzed.
endothermic.
exothermic.
None of the above.

Use the catalyzed reaction mechanism for the decomposition of HCO₂H below to answer questions 8 - 10.

I. HCO₂H + H⁺ HCO₂H₂⁺ (Fast)
II. HCO₂H₂⁺ HCO⁺ + H₂O (Slow)
III. HCO⁺CO + H⁺(Fast)
What is the over-all reaction for the mechanism above?
HCO₂H + H⁺ H₂O + CO + H⁺
HCO₂H₂⁺ CO + H₂O + H⁺
HCO₂H H₂O + CO
HCO₂H₂⁺ HCO⁺+ H₂O
None of the above.
What could be the catalyst?
HCO₂H
H⁺
HCO₂H₂⁺
HCO⁺
CO
Which step is rate-determining?
I
II
III
I and III are both rate-determining.
It is impossible to tell from the information given.

Problem Solving (Show All Work. Use significant figures.)

1. In mixture 4 in the Rate of Reaction lab, you diluted 5.0 mL of 0.20 M KI solution by adding 15 mL of distilled water. What was the concentration of the KI solution after adding the water?

2. In mixture 2 in the Rate of Reaction lab, you mixed 15.0 mL of 0.20 M I^- with 20.0 mL of 0.10 M S₂O₈^2-. They reacted according to the reaction:
2 I^-+ S₂O₈^2- I₂ + 2 SO₄^2-

a) How many moles of I^- and S₂O₈^2-were present in the beginning of the reaction?
b) Which substance (if any) is left over?
c) How much of the substance (if any) is left over?
3. If it took 45 seconds for the clock reaction in the Rate of Reaction lab to turn blue at 25 ^oC, how long would you predict the reaction would take at 15 ^oC? Explain your reasoning.