Koleksi Jawapan Kimia STPM

Koleksi Jawapan Kimia STPM

Answers

5. Reaction Kinetics

1. Explain the activation energy, Ea of exothermic & endothermic?

endo. Ea of forward reaction is larger than backward. exo. Ea of backward reaction is larger than forward.

2. Explain activation energy, Ea vs catalyst?

presence od catalyst will lower the Ea by providing an alternative route from the reaction to occur.

3. Explain activation energy, Ea vs rate of reaction?

higher Ea, slower rate of reaction as less molecules will have energy higher than the Ea.

4. Explain the collision theory?

it is an effective colision involves reactants with the certain minimum energy and the correct orientation of particles.

5. Which more stable (stability) product/ reactants when the ∆H is positive/ negative?

∆H is positive => product is more stable than reactants.
∆H is negative => reactants is more stable than product.

6. Explain frequency of collision vs [reactants] / [products]?

frequency of collision is proportional to only the concentration of the reactants.

7. Explain the effective collision?

effective colision involves reactants with the certain minimum energy and the correct orientation of particles.

8. What depends on rate chemical reaction?

physical state, size of the particles, [concentration], Pressure, Temperature and catalyst but not depends on ∆H.

9. If the product have more energy than the reactants means that?

product are less stable than reactants.

10. Explain Maxwell-Boltzmann distribution curves?

Peak give information about the number of molecules with most probable energy. Area of the two curves is the same. The total number of molecules is the same in both cases.
increasing the temperature, lowers the peak of the curve and shift towards the right hand side.
catalyst does not effect the energy distribution, only lowers the activation energy Ea.

11. Explain rate constant related to temperature?

rate constant always increases with the temperature irrespective of wheater the reaction is endothermic or exothermic.

12. What happens when the volume of vessel increases two times on the concentration of the reactants/ products when reaction occurs?

Increasing the volume two times causes the concentration of reactants* to be halved.
New rate = k[½A]^a [½B]^b. Rate of reaction increases. When the concentration of all the reactants increases, more molecules or ions interact to form new compounds, and the rate of reaction increases. When the concentration of a reactant decreases, there are fewer of that molecule or ion present, and the rate of reaction decreases.

13. How to determine the rate law which related to multiple reaction?

reaction contain multistep species that are only in the rate determaining step only

5. Reaction Kinetics

1. Collision theory is an effective collision involves reactants with the certain minimum energy and the correct orientation of particles.

2. 2NO (g) + Br2 (g) -> 2NOBr (g)

3. Rate equation, rate = k [ NO ]² [ Br2 ]

4. Rate constant is the proportionality coefficient that relates the rate of a chemical reaction (at a given temperature) to the product of the concentration of the reactants (each raised to the power of its order of reaction).

5. Rate determining step….

6. Rate constant always increases with the temperature (or catalyst) irrespective of whether the reaction is endothermic or exothermic.

7. Rate = k [ NO ] ² [ Br2 ]
increasing the volume of vessel two times causes the concentration to be halved.
New rate = k ( ½ [ NO ] ) ² ( ½ [ Br2 ] )
= k ( ¼ [ NO ]² ) ½ [ Br2 ]
= ⅛ k [ NO ] ² [ Br2 ]
= ⅛ (original rate)

8. Rate equation is: Rate = k [ NO ] ² [ O2 ]
New rate when [ NO ] and [ O2 ] increases 2 times. Its 3rd, third order overall. The unit for the rate constant is dm6 m`² s`¹.

9. Draft graph.

10. half life.

11. The rate equation does not provide information about the activation energy but by using Arrhenius equation and plotting the graph ln k vs 1/T.

12. A change in concentration does not affect the rate constant as long as there is no change in the temperature or catalyst.

 

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Answer 17. Hydroxy compounds

1.

3° ROH react with conc H2SO4 heat <140°C or 25°C – 80°C
2° ROH react with conc H2SO4 heat 100°C – 140°C
1° ROH react with conc H2SO4 heat 170-180°C

2.

cold/ room temperature, C=C + 1. H2SO4, 2. warm? with H2O, –> ROH.
or C=C + H2SO4 60 atm, 300 °C –> ROH

3.

3° ROH + [O] –> no reaction
2° ROH + [O] –> ketone + H2O
1° ROH + [O] –> aldehyde -[O]-> RCOOH + H2O

4.

ROH + PCl5 –> RX + HCl (white fume) + POCl3

or react with PCl3, SOCl2, HCl (reflux).

5.

iodoform test give +ve test (yellow ppt), ethanal only, all ketone with 2nd position, 1° & 2° ROH.

6.

using bromine, Br2, phenol = brown colour decolourises. Benzoic acid = no change.

7.

to produce alcohol.
C6H12O6 –> 2C2H5OH + 2CO2

8.
Phenol + Na2CO3 –> no visible reaction/ insoluble.
Benzoic acid –> effervesence, CO2 + H2O/ soluble

9.

Phenol + NaOH –> RO-Na+ + H2 + RCOCl –> ROOR’.

10.

Dehydrogenation to produce:
2° ROH –> ketone
1° ROH –> aldehyde
same with oxidation alcohol but its dehydrogenation.

5. Reaction Kinetics

1. Explain the activation energy, Ea of exothermic & endothermic?

endo.

 

 

 

 

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