6. Kinetics

• Chemistry
• Middelbare school
• vwo
• Leerjaar 5

Topic 6 Kinetics

Class Today (May 10):

Recap of previous class: April 19th

Finish topic 6.1. instruction

LessonUp quiz

Prepare for next weeks' practical (Wed, May 17)

Independent practice 

Tomorrow: HL only, Topic 16.

Recap April 19th

Topic 6: Kinetics

• Collision theory
• Activation energy
• Maxwell-Boltzmann distributions
• Rates of reaction

Collision Theory

Activation energy:

Maxwell-Boltzmann distribution:

Rates:

'The rest' of topic 6:

Measuring rates of reaction experimentally

•                 Production of a gas
•                 Measuring ion concentrations

•                 Measuring the time taken for precipitation

                

Factors that affect rates of reaction 

Measuring the production of a gas

Example: Reaction between calciumcarbonate and HCl

...Or we measure the decrease in mass as the CO2 escapes 

Measuring ion concentrations 

Ions in solution conduct electricity, can be measured with a voltmeter

H+ ion concentrations can be measured continuously with a pH probe

Another way is to take samples of reaction mixture 

and cool them down very quickly

(quenching), 

then determine ion concentrations

by titration. 

Measuring the time taken for the formation of a precipitate

Factors affecting the rate of reaction

 Temperature has 2 effects:

1. Collision frequency goes up

2: A bigger proportion of molecules will have energy > E_a

Factors affecting the rate of reaction

Concentration (in solution): the higher the concentration of the reactants, the higher the reaction rate. 

Pressure (in gases): the higher the pressure, the higher the reaction rate.

Why? Higher collision frequency

Factors affecting the rate of reaction

Particle

size

Factors affecting the rate of reaction

The role of a catalyst

Q1. Which of the following factors are important in determining whether a reaction takes place or not?
I: The energy of the colliding molecules
II: The orientation of the colliding molecules

1. I only
2. II only
3. Both I and II
4. Neither I nor II

Q2: Which statements explain the increase in the rate of reaction when the temperature is increased:
I: More particles have energy greater than the activation energy
II: The frequency of collisions increases
III: The activation energy decreases

1. I and II only
2. I and III only
3. II and III only
4. I, II and III

Q3: Iodine reacts with hydrogen according to the following equation:

I2 (g) + H2 (g) ⇌ 2HI (g)

Why do not all collisions between H2 and I2 molecules result in a chemical reaction?

1. The colliding molecules have the incorrect orientation
2. The colliding molecules have very high kinetic energies
3. The temperature of the reaction system is too high
4. The activation energy for the reaction is too low

Q4: Which of the following statements applies to a collision between reactant particles that leads to a chemical reaction?

1. The colliding particles must have different energies
2. The colliding particles must have energy equal to or greater than the activation energy.
3. The colliding particles must have equal energy.
4. The colliding particles must have an activation energy of greater than 50 kJ mol-1.

Q5: A sealed container is filled with two reactant gases and the temperature is increased which leads to an increase in the rate of reaction. Which of the following statements is/are true?
I. The number of particles in the mixture increases.
II. The average kinetic energy of the particles increases.
III. A greater proportion of reactant particles have energy greater than the activation energy for the reaction.

1. I only
2. II only
3. II and III only
4. I and II only

Q6: If the activation energy 2 is left of activation energy 1 (on the x-axis), why is that reaction path faster?

1. More frequent collisions between the particles occur
2. More energetic collisions between the particles occur
3. A catalyst has been added
4. The temperature is higher

Q7: Which is NOT affected by a change in temperature?

1. Rate of reaction
2. Collision Frequency
3. Collision geometry
4. % of molecules with E > activation E

Q8: Which of the following is the correct unit for the rate of reaction?

1. mol dm-3
2. mol
3. dm3
4. mol dm-3 s-1

Q9:

1. a colorimeter
2. a gas syringe
3. a stopwatch
4. a pH meter

Q10: Which of the following reactions could be studied by measuring the volume of a gas produced by unit time?
1. The reaction of magnesium and sulfuric acid
2. The reaction of hydrochloric acid and sodium hydroxide
3. The reaction of calcium carbinate and hydrochloric acid

1. 2 only
2. 3 only
3. 1 and 2 only
4. 1 and 3 only

End of the quiz

Questions???