Rates of reaction

Question 1

What is the word definition for the units of rate?

Answer 1

Concentration per unit time.

Question 2

What is the rate eqn?

Answer 2

Rate = k [A]^x [B]^y for the reaction A + B → C + D

Question 3

What are the units for the the following when the overall order of the reaction is 1, 2, 3, 4, 5

Answer 3

1 = s^-1
2 = mol^-1dm3 s^-1
3 = mol^-2dm6 s^-1 
4 = mol^-3dm9 s^-1
5 = mol^-4dm12 s^-1

Question 4

What affects the rate of a reaction?

Answer 4

1. Temperature
2. Pressure
3. Concentration
4. Presence of a catalyst

Question 5

How do you measure the rate if the substance is coloured?

Answer 5

A colorimeter is used alongside a calibration curve.

Question 6

How do you measure the rate of reaction when they are gaseous?

Answer 6

Gas syringe can be used to measure gas volume, or the change in mass can be recorded.

Question 7

How do you measure the rate if the sample can be titrated?

Answer 7

A sample can be taken, and quenched and titrated to determine concentration. Quenching can be chemical or by cooling.

Question 8

What do you do of OH- / H+ ions present

Answer 8

If H+/OH- are a reactant or product, the change in pH can be measured with a pH meter.

Question 9

What is the initial rate method?

Answer 9

Choose a product that is measurable. For one reactant set up a series of experiments using a range of concentrations. Plot graphs of measurable quantity against time. Determine initial rate at t=0s by drawing a tangent at t=0s and calculating its gradient. The gradient of this line is the initial rate of reaction.

Question 10

Draw the zero order, first order and second order graphs of rate against concentration.

Answer 10

in book

Question 11

What is the progressive rate method?

Answer 11

1. pH meter for [H+] ion concentration. Make sure no other ions interfere.
2. Colorimeter - absorbance values of a coloured reactant the calibration curve
3. Titration - concentration of a specific reactant

Question 12

Draw the graphs for zero order, first order and second order of concentration against time

Answer 12

in book

Question 13

How do you quench a reaction

Answer 13

Add large quantities of cold water or chemical quenching

Question 14

How are halogenoalkanes hydrolyses?

Answer 14

Hydrolysed by OH- ions by nucleophilic substitution

Question 15

Draw and explain the diagram for the hydrolysis of a primary halogenoalkane

Answer 15

Undergo SN2 hydrolysis.
General rate equation: rate = k[1º Halogenoalkane][OH-]
Over all order = 2
drawing in book

Question 16

Draw and explain the diagram for the hydrolysis of a tertiary halogenoalkane

Answer 16

Undergo SN1 hydrolysis
General rate equation: rate = k [3º Halogenoalkane]
Overall order = 1
drawing in book