Chapter 6 Chemical Kinetics

Question 1

Collision theory

Answer 1

Sufficient kinetic energy
Must collide (physical contact)
Proper orientation

Question 2

Rate of reaction

Answer 2

change in concentration of a particular reactant/product per unit time

Question 3

Activation Energy Ea

Answer 3

minimum energy needed for colliding molecules to have a succesfull collision leading to a reaction.
minimum energy needed for a reaction to take place.

Question 4

Ea catalyst

Answer 4

increases the rate of chemical reaction without being chemically absorbed/changed.

Question 5

Average speed/rate

Answer 5

change in concentration/time taken
mol dm^-3 s^-1
greater than 0
graphically = gradiant of secant, determined from gradienat of tangent line (concentration time graph)

Question 6

Instantaeous rate

Answer 6

dc/dt or c’(t)

equals gradient of a tangent

Question 7

Initial rate

Answer 7

when t=1 (t0)

Question 8

How to measure rate

Answer 8

• If gas is formed, the volume of the gas could be measured at regular intervals.
• If the pH or electrical conductivity changes during the reaction, this could be measured at regular time intervals.
• Likewise of color changes.

Question 9

Collision theory factors

Answer 9

• Temperature (higher temperature -> higher rate)
• Pressure (for gases) higher pressure -> greater rate
• Catalysts increase rate
• Light (for some reactions) increases rate
• Increased surface increases rate
• Increasing concentration increases frequency of collisions -> increases rate
• Decreasing particle size (solid phase) -> increases surface area

Question 10

Rate equation

Answer 10

If aA + bB = cC + dD then rate =

Question 11

Energy profile

Answer 11

graph-ish of activation energy with and without catalyst.
Exothermic reaction = reactants “higher” than products.
Endothermic reaction = reactants “lower” than prooducts.

Question 12

Transition state/activated complex

Answer 12

Arrangment of atoms at crest of energy profile -bonds are about to break or form.

Question 13

Energy profile catalysts

Answer 13

Catalysts decrease acitvation energy by providing an alternative pathway for the reaction, speeding it up.

Question 14

Homogenous catalysis

Answer 14

catalysts and reactants are in the same phase

e.g. Ozone

Question 15

Heterogeneous catalysis

Answer 15

reactants and catalysts are in different phases. Typically with gaseous and liquid reactants and a solid catalyst.

Question 16

The Maxwell-Boltzmann energy distribution curve

Answer 16

Illustrates different speeds and energies.
White area (to the left) shows amount of particles lacking energy to react.
Dotted line shows activation energy Ea
Blue/shaded area (to the right) shows amount of particles with enough energy to react.