Reaction Kinetics

Question 1

Rate of reaction

Answer 1

Change in concentration of reactant consumed or product produced per unit time.

Question 2

Half-life of a reaction, t(1/2)

Answer 2

The amount of time needed for concentration of reactant to fall to half its initial value.

Question 3

What is rate constant, k, dependent on?

Answer 3

1) Temperature 2) Activation Energy

Question 4

Zero-ordered Rxn:

Answer 4

Eqn: Rate = K[a]^0
Rate-[A] Graph: Straight horizontal line
[A]-T graph: Straight decreasing graph
K unit = mol dm-3 s-1

Question 5

First-Order Reaction

Answer 5

Eqn: Rate = K[a]
Rate-[A] Graph: Straight increasing graph passing through origin
[A]-T graph: Curve that is decreasing 
K unit = s-1
Unique: Has half-life

Question 6

Equation of half-life

Answer 6

T(1/2) = ln2/k

Question 7

Number of half life elapsed

Answer 7

[A1]/[A2] = (0.5)^n

Question 8

Second-Order rxn

Answer 8

Eqn: Rate = K[a]^2
Rate-[A] Graph: half of x^2 graph
Rate-[A]^2 graph: Straight increasing graph
[A]-T graph: Straight decreasing graph but t(1/2) not constant
K unit = mol-1 dm3 s-1

Question 9

When can Pseudo First-order Rxn occur

Answer 9

1) When one of Rxt is in large excess

2) When one of Rxt is also the solvent

Question 10

How to use inspection method

Answer 10

“Comparing Expt _ and _ when [] and [] are constant
When [the one uw find] is increased/decreased by __ times, initial rate is increased/decreased by __ times.
Hence, rxt is __-order wrt [~]”

Question 11

How to answer half life thingy

Answer 11

“Since half-life is (approximately) constant at ___ mins, the reaction is first-order wrt [__]”

Question 12

Collision Theory

Answer 12

A) Chemical reaction occur as a result of particles colliding with one another
B) Only particles which collide with energy greater or equal to Activation Energy, Ea, will be able to react. These Collisions are called effective collisions.

Question 13

Activation Energy

Answer 13

The minimum energy molecules need to possess for a reaction to occur

Question 14

Factors affecting rate of reaction

Answer 14

1) Size of Particle
2) Concentration / Pressure of a gas
3) Temperature
4) ) Catalyst

Question 15

How does particle size affect rate?

Answer 15

^ Surface area of a solid reactant -> ^ Frequency of effective collisions between X and Y -> ^Rate

Question 16

How does concentration/pressure affect rate?

Answer 16

^Pa/[_] -> Particles are closer -> ^Number of collision -> ^Frequency of effective collision -> ^ Rate

Question 17

How does temp affect rate?

Answer 17

^Temp -> ^ KE and move about faster -> ^Number of particles having energy greater than or equal to Ea -> ^Frequency of effective collisions-> ^ Rate

Question 18

On Boltzmann Distribution Curve, when Temp increases what changes

Answer 18

Peak go rightward + lower

Amt of particle at Ea is increased

Question 19

How does catalyst affect rate?

Answer 19

Catalyst provides an alternative reaction pathway with lower activation Energy, Ea
Number of particles having energy greater than or equal to the Ea increases
Frequency of effective Collision increases
Rate increase

Question 20

Catalyst

Answer 20

A substance that increases the rate of chemical reaction with itself being regenerated and chemically unchanged at the end of the reaction.

Question 21

Type of Catalyst

Answer 21

1) Heterogenous Catalyst
2) Homogenous Catalyst
3) Autocatalyst
4) Enzymes

Question 22

How does heterogeneous catalyst work

Answer 22

1) Reactants are adsorbed onto catalyst surface
2) Due to availability of 3d and 4s electron, catalyst will form weak bond with the reactants. This weakens the bond in the reactant molecules. This a) lower Ea and 2) Increases surface concentration
3) When product is formed, they are desorbed from the catalyst surface

Question 23

How to quench

Answer 23

1) Use large amt of cold water to lower [reactant] and slow down the reaction
2) Quenching agent to react immediately with one of reactant and stop rxn
3) Inhibitor/Negative Catalyst to slow down rxn