Princeton Ch 9 - Kinetics

Question 1

Chemical kinetics.

Answer 1

Chemical kinetics is the study of how reactions take place and how fast they occur.

Question 2

Intermediate.

Answer 2

A substance that is produced in one elementary step and then consumed in a subsequent step.

Question 3

Which step in a reaction determines its overall rate?

Answer 3

The slowest step in a process determines the overall reaction rate. No matter how fast the preceding steps move along, the intermediates will pile in front of this step.

Question 4

Reaction rate.

Answer 4

How fast reactants are being consumed or how fast products are being formed.

Question 5

What three things determine reaction rate?

Answer 5

1) How frequently the reactant molecules collide.
2) The orientation of colliding molecules.
3) their energy.

Question 6

Activation energy.

Answer 6

The minimum energy required of a reactant molecule during a molecular collision in order for the reaction to proceed to the product. f the reactants don’t possess this much energy, their collisions won’t be able to produce the products and the reaction will not occur.

Question 7

Transition state.

Answer 7

If reactants possess the necessary activation energy, they can reach a high-energy (and short-lived) transition state.

Question 8

Another name for transition state.

Answer 8

Activated complex.

Question 9

True or false. The transition state is always an energy maximum.

Answer 9

True.

Question 10

The lower the activation energy, the (faster/slower/no change) the reaction rate.

Answer 10

The lower the activation energy, the faster the reaction rate.

Question 11

The greater the concentration of the reactants, the (faster/slower/no change) the reaction rate.

Answer 11

The greater the concentration of the reactants, the FASTER the reaction rate. Favorable collisions are more likely as the concentration of the reactant molecules increase.

Question 12

The higher the temperature of the reaction mixture, the (faster/slower/no change) the reaction rate.

Answer 12

At high temps, more reactant molecules have a sufficient energy to overcome the activation energy barrier, and molecules collide at a higher frequency, so the reaction can proceed at a faster rate.

Question 13

Are thermodynamic and kinetic factors dependent on one another?

Answer 13

No. Thermodynamic factors (reactants, intermediates, products, ΔG°) and kinetic factors (activation energy) DO NOT affect each other. Also, remember ΔG° stays the same.

Question 14

Catalyst.

Answer 14

A catalyst almost always makes a reaction go FASTER by either speeding up the rate-determining step or providing an optimized route to products.

Question 15

How does a catalyst speed up a reaction?

Answer 15

By lowering the activation energy/barrier of the rate determining step, and therefore the energy of the highest transition state.

Question 16

What’s a key difference between a reactant and a catalyst?

Answer 16

Reactants are converted to products while a catalyst remains unchanged at the end of a reaction. A catalyst can undergo temporary change during a reaction, but it is always converted back to its original state.

Question 17

Does the addition of a catalyst affect any of the following quantities: ΔG, ΔH, ΔS.

Answer 17

The addition of a catalyst will affect the rate of a reaction, but not the equilibrium or the thermodynamics of the reaction. A catalyst doesn’t change any of the thermodynamic quantities such as ΔG, ΔH, ΔS.

Question 18

True or false. A catalyst only decreases the activation energy of the forward reaction.

Answer 18

Catalysts decrease the activation energy of the forward reaction and the reverse reaction.