(also, transition state) unstable combination of reactant species formed during a chemical reaction

activation energy (E_a)

minimum energy necessary in order for a reaction to take place

mathematical relationship between a reaction’s rate constant, activation energy, and temperature

model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics

proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation

used in chemical kinetics to illustrate various properties of a reaction

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Chemistry 2e · 12.5 Collision Theory

Collision Theory: practice problems

9 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 50
Chemical reactions occur when reactants collide. What are two factors that may prevent a collision from producing a chemical reaction?
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Exercises 52
What is the activation energy of a reaction, and how is this energy related to the activated complex of the reaction?
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Exercises 54
Describe how graphical methods can be used to determine the activation energy of a reaction from a series of data that includes the rate of reaction at varying temperatures.
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Exercises 56
The rate of a certain reaction doubles for every 10 °C rise in temperature.
(a) How much faster does the reaction proceed at 45 °C than at 25 °C?
(b) How much faster does the reaction proceed at 95 °C than at 25 °C?
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Exercises 58
The rate constant at 325 °C for the decomposition reaction $C_{4} H_{8} ⟶ 2 C_{2} H_{4}$ is 6.1 $\times$ 10⁻⁸ s⁻¹, and the activation energy is 261 kJ per mole of C₄H₈. Determine the frequency factor for the reaction.
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Exercises 60
An elevated level of the enzyme alkaline phosphatase (ALP) in human serum is an indication of possible liver or bone disorder. The level of serum ALP is so low that it is very difficult to measure directly. However, ALP catalyzes a number of reactions, and its relative concentration can be determined by measuring the rate of one of these reactions under controlled conditions. One such reaction is the conversion of p-nitrophenyl phosphate (PNPP) to p-nitrophenoxide ion (PNP) and phosphate ion. Control of temperature during the test is very important; the rate of the reaction increases 1.47 times if the temperature changes from 30 °C to 37 °C. What is the activation energy for the ALP–catalyzed conversion of PNPP to PNP and phosphate?
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Exercises 62
Hydrogen iodide, HI, decomposes in the gas phase to produce hydrogen, H₂, and iodine, I₂. The value of the rate constant, k, for the reaction was measured at several different temperatures and the data are shown here:
Temperature (K) k (L mol⁻¹ s⁻¹)
555 6.23 $\times$ 10⁻⁷
575 2.42 $\times$ 10⁻⁶
645 1.44 $\times$ 10⁻⁴
700 2.01 $\times$ 10⁻³
What is the value of the activation energy (in kJ/mol) for this reaction?
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Exercises 64
The hydrolysis of the sugar sucrose to the sugars glucose and fructose,
$C_{12} H_{22} O_{11} + H_{2} O ⟶ C_{6} H_{12} O_{6} + C_{6} H_{12} O_{6}$
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Exercises 66
Use the PhET Reactions & Rates interactive simulation to simulate a system. On the “Single collision” tab of the simulation applet, enable the “Energy view” by clicking the “+” icon. Select the first $A + B C ⟶ A B + C$ reaction (A is yellow, B is purple, and C is navy blue). Using the “angled shot” option, try launching the A atom with varying angles, but with more Total energy than the transition state. What happens when the A atom hits the BC molecule from different directions? Why?
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Key terms · 6

activated complex: (also, transition state) unstable combination of reactant species formed during a chemical reaction
activation energy (E_a): minimum energy necessary in order for a reaction to take place
Arrhenius equation: mathematical relationship between a reaction’s rate constant, activation energy, and temperature
collision theory: model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics
frequency factor (A): proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation
reaction diagram: used in chemical kinetics to illustrate various properties of a reaction

Learn 12.5 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 12.5 in the textbook · This section on openstax.org

Collision Theory: practice problems

9 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 50

Chemical reactions occur when reactants collide. What are two factors that may prevent a collision from producing a chemical reaction?

Exercises 52

What is the activation energy of a reaction, and how is this energy related to the activated complex of the reaction?

Exercises 54

Describe how graphical methods can be used to determine the activation energy of a reaction from a series of data that includes the rate of reaction at varying temperatures.

Exercises 56

The rate of a certain reaction doubles for every 10 °C rise in temperature.

(a) How much faster does the reaction proceed at 45 °C than at 25 °C?

(b) How much faster does the reaction proceed at 95 °C than at 25 °C?

Exercises 58

The rate constant at 325 °C for the decomposition reaction $C_{4} H_{8} ⟶ 2 C_{2} H_{4}$ is 6.1 $\times$ 10⁻⁸ s⁻¹, and the activation energy is 261 kJ per mole of C₄H₈. Determine the frequency factor for the reaction.

Exercises 60

An elevated level of the enzyme alkaline phosphatase (ALP) in human serum is an indication of possible liver or bone disorder. The level of serum ALP is so low that it is very difficult to measure directly. However, ALP catalyzes a number of reactions, and its relative concentration can be determined by measuring the rate of one of these reactions under controlled conditions. One such reaction is the conversion of p-nitrophenyl phosphate (PNPP) to p-nitrophenoxide ion (PNP) and phosphate ion. Control of temperature during the test is very important; the rate of the reaction increases 1.47 times if the temperature changes from 30 °C to 37 °C. What is the activation energy for the ALP–catalyzed conversion of PNPP to PNP and phosphate?

Exercises 62

Hydrogen iodide, HI, decomposes in the gas phase to produce hydrogen, H₂, and iodine, I₂. The value of the rate constant, k, for the reaction was measured at several different temperatures and the data are shown here:

Temperature (K)	k (L mol⁻¹ s⁻¹)
555	6.23 $\times$ 10⁻⁷
575	2.42 $\times$ 10⁻⁶
645	1.44 $\times$ 10⁻⁴
700	2.01 $\times$ 10⁻³

What is the value of the activation energy (in kJ/mol) for this reaction?

Exercises 64

The hydrolysis of the sugar sucrose to the sugars glucose and fructose,

$C_{12} H_{22} O_{11} + H_{2} O ⟶ C_{6} H_{12} O_{6} + C_{6} H_{12} O_{6}$

Exercises 66

Use the PhET Reactions & Rates interactive simulation to simulate a system. On the “Single collision” tab of the simulation applet, enable the “Energy view” by clicking the “+” icon. Select the first $A + B C ⟶ A B + C$ reaction (A is yellow, B is purple, and C is navy blue). Using the “angled shot” option, try launching the A atom with varying angles, but with more Total energy than the transition state. What happens when the A atom hits the BC molecule from different directions? Why?

Key terms · 6

activated complex: (also, transition state) unstable combination of reactant species formed during a chemical reaction
activation energy (E_a): minimum energy necessary in order for a reaction to take place
Arrhenius equation: mathematical relationship between a reaction’s rate constant, activation energy, and temperature
collision theory: model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics
frequency factor (A): proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation
reaction diagram: used in chemical kinetics to illustrate various properties of a reaction

Learn 12.5 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 12.5 in the textbook · This section on openstax.org