Kinetics: Maxwell–Boltzmann Distribution

Question 1

What is a Maxwell-Boltzmann distribution curve?

Answer 1

• Graph that shows the distribution of the molecular energies in a gas at a constant temperature
• The area under the curve indicates the total number of particles present

Question 2

What does a standard Maxwell-Boltzmann distribution show?

Answer 2

• The curve starts at (0,0) because no molecules have zero energy
• Graph never touches x-axis
• Some have very low and some have very high energies/velocities
• Most have intermediate velocities
• The peak of curve shows the most probable energy (the most likely energy of a single molecule)
• Area shows total number of particles
• Activation energy line - molecules to the right of this line can react

Question 3

What is the effect of increased temperature on a Maxwell-Boltzmann distribution?

Answer 3

• Curve gets a shift to higher energies/velocities
• Peak moves to right
• Curve gets broader and flatter due to the greater spread of values
• Area under curve stays constant
• Increasing the temperature gives more particles an energy greater than Ea

Question 4

What is the effect of decreased temperature on a Maxwell-Boltzmann distribution?

Answer 4

• Curve gets a shift to lower energies/velocities
• Peak moves to left
• Curve gets narrower and more pointed due to the smaller spread of values
• Area under curve stays constant
• Decreasing the temperature gives less particles an energy greater than Ea

Question 5

What is the effect of increased concentration on a Maxwell-Boltzmann distribution?

Answer 5

• Shape of curve is same, but raised
• The most probable energy (Emp) of both curves are the same
• The area under the curve to the right of the Ea is greater at higher concentrations
• More particles can react
• Total area under the curve is greater at higher concentrations

Question 6

What is the effect of adding a catalyst on a Maxwell-Boltzmann distribution?

Answer 6

• The Maxwell-Boltzmann distribution curve is unchanged in shape
• Position of activation energy is shifted to the left
• Greater proportion of molecules have sufficient energy to react

Question 7

How can the mean energy of molecules be found on a Maxwell-Boltzmann distribution?

Answer 7

• The mean energy of all molecules is a bit to the right of the peak