Expt 1-Factors Affecting Reaction Rate

Factors Affecting Reaction Rate

Lascano Normilando P. V

Lavarias Alyssa Katrina G.

Introduction

• Chemical reactions occur at different rates.

• Rate is the speed at which the reaction takes place and is influenced by several factors.

• Collision theory and the transition-state theory

Factors Affecting Reaction Rate

• Nature of Reactants• Concentration• Surface Area• Temperature• Presence of catalysts

What affects the rates?

Factors Affecting Reaction Rate

What affects the rates?

• Nature of Reactants- The lesser the stability of the reactant, the

higher its kinetic energy, the greater its reactivity

- In general, reaction that goes proceeds fast have low activation energy.

Factors Affecting Reaction Rate

What affects the rates?

• Concentration- The effect of the change in concentration

reactants can be summarized in the Rate Law Expression

Rate = k[A]x[B]y

- For most reactions, RLE is more concerned with the amount of the reactant present than the product.

Factors Affecting Reaction Rate

What affects the rates?

• Surface Area– The greater the amount of area exposed, the higher

the rate as it offers greater amount of the reactant available for collision

• Temperature- By increasing the temperature, the average KE of the

system also increases making it more entropic, which also increases the frequency of effective collisions.

Factors Affecting Reaction Rate

What affects the rates?

• Presence of catalysts- Catalysts are substances that speed up or slow

down the rate of reaction without being altered.- In Homogenous catalysis, the catalyst alters the

rate by providing an alternative pathway with a different activation energy for the reaction.

- Heterogenous catalysts are usually solid, and it distorts the rate by providing a “breeding” grounds for the reaction

Factors Affecting Reaction Rate

Procedure : Nature of Reactants

Procedure : Concentration

10 ml beaker on top of white

paper marked with X

Constant [HCl]Treatments:

1.5.ml 0.15M Na2S2O3 + 1ml 3M HCl2.4mL 0.15M Na2S2O3 + 1mL H2O 1ml 3M HCL3.3mL 0.15M Na2S2O3 + 2mL H2O 1ml 3M HCL4.2mL 0.15M Na2S2O3 + 3mL H2O 1ml 3M HCL5.1mL 0.15M Na2S2O3 + 4mL H2O 1ml 3M HCL

Constant [Na2S2O3]Treatments:

1.5.ml 0.15M Na2S2O3 + 2.5ml 3M HCl2.5.ml 0.15M Na2S2O3 + 2ml 3M HCl + 0.5ml H2O3.5.ml 0.15M Na2S2O3 + 1.5ml 3M HCl + 1ml H2O4.5.ml 0.15M Na2S2O3 + 1ml 3M HCl + 1.5ml H2O5.5.ml 0.15M Na2S2O3 + 0.5ml 3M HCl + 2ml H2O

Record reaction time

Procedure : Surface Area

Procedure : Temperature

Test tubes 1 and 2

Test tube 1:5ml of 0.15M

Na2S2O3

Test tube 2:7.5 ml H2O + 2ml 3M HCl

Water bath for 5minRecord Temp

Mix reagents; record rxn

time (X mark)

Repeat process for 2 different

temp

Procedure : Catalysts

Results:

• Nature of Reactants:– A. Mg —slow reaction; little bubble formation– B. Na —fast reaction; evolution of gas– because Na reacted faster than the Mg, it

must have a relatively lower activation energy

• Concentration of Reactants

• Constant [HCl]

Results:

• Concentration of Reactants

• Constant [Na2S2O3]

Results:

• Temperature[Na2S2O3] = 0.052M

M1V1/V2=M2

(0.15M)(5mL)/(14.5mL)=M2

M2=0.0517

[HCl] =0.414

(3M)(2mL)/(14.5mL)=M2

M2=0.4138

Results:

• Surface AreaStrip of Mg - Slow bubble formation

Piece of Mg - Relatively faster bubble formation

• CatalystH2O2 + Rochelle salt: Slow rxn; White granules visible on

the wall of the tube

H2O2 + Rochelle salt + CoCl2: Fast rxn; turned brown and back to pinkish hue

Results:

Discussion

• The nature or kind of reactant plays a key role in the determination of reaction rate. When a reactant has a low Ea or activation energy the faster the speed of the reaction and higher rate.

• It is understandable that reaction goes faster when reactants are in higher concentration as that offers a higher possibility of the particles colliding or making contact with each other. In altering the concentration, the Ea is unchanged however, it increases the frequency of the reactant “collision.”

Discussion

• When subjected to varying temperature (consider treatments of the same solution) resulting rates also varies. Almost all reaction proceeds faster with an increase in temperature. This is because heating increases the energy of the particles, making the move faster hence more entropic which increases the frequency of collision.

Discussion

• The amount of exposed area of reactants can pose a difference in the rates likewise. Greater surface area available for contact means greater amount of particles can be collided.

• Catalysts are substances that alter the speed (in this case, speed up) of reaction without being consumed. It offers an alternative pathway for the reaction to go on by either lowering the energy threshold—homogenous catalysis—or by providing a surface for the reaction to take place—heterogenous catalysis.

Discussion

Conclusion

• In this experiment, it is palpable that under different experimental conditions the reaction rate differs. Several factors affect reaction rate via different approaches.

Recommendations

• Accuracy if not precision is a must in situations that results are very much reliant upon several factors.

• In this experiment, observed data differs from that of the theoretical. It can only be concluded that there exist faults either in the observer itself or in the environment in which the experiment was concluded.

• It is recommended therefore that experiments in general must be carried out in conducive environment.

• It would also be very advisable to have a preliminary discussion of the experiment so as to have a better understanding of the topic not just in theoretical aspect but also practically as the discussion would justify the gathered results.

Recommendations

• It would be better also if the experiment was given enough time to be done. It was noted that the experiment that is supposed to be done in a meeting was forced to be finished in half the time.

Recommendations