1.9 Rates of Reaction

Question 1

What is the rate of reaction measured in?

Answer 1

The increase of [products] or the decrease in [reactants]

Question 2

What is the rate equation?

Answer 2

Rate= k[A]^m[B]^n

Question 3

What do orders mean?

Answer 3

Order=0 if changing conc doesn’t change rate
Order=1 if doubling conc doubles the rate
Order=2 if doubling conc quadruples rate

Question 4

What is the rate determining step?

Answer 4

The step in a mechanism that determines what order a reaction is which are then involved in the rate equation

Question 5

What is the definition of an order?

Answer 5

The number of molecues of each species in the rate dependent step

Question 6

What are the units of rate if the total order is 0?

Answer 6

Moldm^-3s-1

Question 7

What are the units if the total order is 1?

Answer 7

S^-1

Question 8

How do you find the order from a data table?

Answer 8

1. Pick two rows where one of the concentrations remain constant
   2.Calculate the change by dividing one by the other of the concentrations of substance you want the order if
   3.Calculate the change in rate
2. If rate doesn’t change - Order 0
   If rate changes the same as the concentration- Order 1
   If rate changes double the amount of the concentration- Order 2

Question 9

What is the iodine clock measuring?

Answer 9

The rate for iodide ions to become iodine

Question 10

How is the iodine clock experiment able to be measured?

Answer 10

Iodine produced will react with sodium thiosulfate until thiosulfate runs out forming Iodide ions again

Question 11

Why are initial rates used in rate calculations?

Answer 11

The concentrations are known

Question 12

How is the initial rate obtained from a graph?

Answer 12

Tangent at the start of the curve

Question 13

What happens to the rate equation if a large concentration of one reactant is added in comparison to the others?

Answer 13

Concentration will be high enough that it is a constant

Question 14

What is the opposite of exponential in the Arrhenius equation?

Answer 14

Natural log

Question 15

What are the only things which affect the rate constant?

Answer 15

Temperature
Catalysts

Question 16

What is the Arrhenius constant in reference to?

Answer 16

• The frequency of collisions
• Varies only slightly with temperature so taken as a constant

Question 17

What are the units of activation energy in the Arrhenius equation?

Answer 17

J/mol

Question 18

What denotes the order in the rate determining step?

Answer 18

The number of particles involved

Question 19

Why does increasing the temperature make a reaction go faster?

Answer 19

Particles have more kinetic energy so more frequent collisions
More particles with a greater frequency of successful collisions

Question 20

What does a catalyst do and how does it do it?

Answer 20

• Speeds up the rate of reaction
• Providing a lower activation energy through an alternative reaction route

Question 21

Why in terms of particles does adding a catalyst make the reaction go faster?

Answer 21

• E >/= Ea
• More particles with a greater frequency of successful collisions
• Increases rate of reaction

Question 22

How can the rate equation be calculated from the overall equation?

Answer 22

• Not possible

Question 23

What is the definition of a mechanism?

Answer 23

• The breakdown of steps in a reaction

Question 24

How can a chemical be put into a rate equation but not the overall equation?

Answer 24

Catalysts as they are part of the rate determining step but not the overall equation

Question 25

What SN number would the hydrolysis of a primary haloalkanes be?

Answer 25

SN2 as two molecules are involved in the slowest step

Question 26

Why do different mechanisms take place depending on the primary,secondary or tertiary haloalkanes?

Answer 26

• Primary carbocations are the least stable tertiary carbocations are the most due to more alkyl induction with tertiary having three alkyl groups so more electron density on the carbocation making it more stable

Question 27

What is in the rate determining step but not in the rate equation?

Answer 27

Intermediates

Question 28

How can the mechanism of a reaction be found?

Answer 28

Experiment using either initial rate or continuous measuring which gives rate vs change in concentration
Then find the order using the graph or through calculate using data tables