Experiment #1:Factors Affecting Reaction RatesGaring, Pia Vianca Nikka Q.Tolentino, Chelsea Reyna

Introduction

Chemical reactions - reactants being converted into products

rate of reaction - change of concentration of reactants or products over time (M/s)

Collision Theory - a reaction is made when molecules collide

rate of reaction number of collisions/second

Transition State Theory

Introduction

Factors Affecting Reaction Rates:Nature of reactantsConcentrationTemperatureSurface AreaPresence of Catalyst

Objectives of the Experiment

To determine the effects of some factors on reaction rates

To determine the rate law expression using the method of initial rates

To evaluate the value of the activation energy of a reaction

A. Nature of the Reactants

• Record observations.

Test Tube A

3mL water+

Mg ribbon

Test Tube B

3mL water+

piece of Na

B. Concentration of Reactants

0.15M Na2S2O3 (mL) H2O(mL) 3M HCL (mL)

4 1 1

3 2 1

2 3 1

1 4 1

Constant HCl Concentration

• 10mL beaker on top of white paper marked with X

• Record reaction time.

B. Concentration of Reactants

0.15M Na2S2O3 (mL) H2O(mL) 3M HCL (mL)

5 0 2.5

5 0.5 2.0

5 1.0 1.5

5 1.5 1.0

5 2.0 0.5

Constant Na2S2O3 Concentration

• 10mL beaker on top of white paper marked with X

• Record reaction time.

C. Temperature

Test tube #1: 0.15M Na2S2O3

Test tube #2: 7.5mL H2O + 2mL 3M HCl

• Water bath for about 5mins.

• Measure and record temperature

• Mix reagents in 50mL beaker on top of white paper marked with X

• Time reaction (like in Part B)

• Repeated with 6C and 50C

D. Surface Area

Test tube #1:Strip of Mg

Test tube #2:Pieces of Mg

• Add 5mL 3M HCl solution

• Record observations

E. Catalyst

Test tube #1:H2O2 +Rochelle salt (sodium potassium

tartrate)

Test tube #2:H2O2 +Rochelle salt (sodium potassium tartrate)+ CoCl2

• Heat solutions gently.

• Record observations.

Results and DiscussionPart A. Nature of reactants

Results and DiscussionPart B. Concentration of Reactants

Table 1. Constant HCl concentration

Table 2. Constant [Na2 S2O3]

Collision Theory - a reaction is made when molecules collide

rate of reaction number of collisions/second

increase in concentration

=

increase in the number of molecules

=

increase in the number of collisions

Rate Law

rate= k[reactant 1]m[reactant 2]n . . .

k=rate constant

m and n = order of reaction

Results and Discussion

-3.8 -3.6 -3.4 -3.2 -3 -2.8 -2.6 -2.4 -2.2 -2 -1.8

-7

-6

-5

-4

-3

-2

-1

0ln [Na2S2O3]

ln ra

te

Figure 1.Graphical Plot of ln [Na2S2O3] vs.ln rate

Slope = Order of the substance = 1.77 ≈

2

Part B. Concentration of Reactants

Results and Discussion

-1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0

-3.8-3.7-3.6-3.5-3.4-3.3-3.2-3.1

-3-2.9-2.8

ln [HCl]

ln ra

te

Figure 2. Graphical plot of ln[HCl] vs. ln rate

Slope = 0.35 ≈ 0

rate= k[Na2 S2O3]2 [HCl]0

Part B. Concentration of Reactants

Results and Discussion

0.003 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0 1/T (in K)

ln

k

Table 3. Effect temperature on the rate of reaction

Figure 3. Graphical plot 1/T vs. ln k

Part C. Temperature

Results and Discussion

A change in temperature also changes the rate of a reaction.

The kinetic energy in the molecules increase as the temperature increases. Arrhenius equation k= Ae^ (-Ea/RT)

Part C. Temperature

Results and Discussion

Strips of Mg ribbon vs. Uncut Mg ribbon

- both reacts with the 3M HCl

- relatively faster - slower

*Collision theory

Part D. Surface Area

Results and Discussion

- a substance that speeds up the reaction by lowering the activation energy

Reactants Visible result

H2O2 + Rochelle salt The mixture is clear at first but when heated, it formed bubbles and turned light yellow in color.

H2O2+ Rochelle salt + CoCl2

Reacted immediately upon the addition of CoCl2. Bubbles formed.

Part E. Catalyst

Conclusion

The rate of the reaction is affected by concentration, temperature, nature of reactants, catalyst and surface area

The collision theory explains how the number of collisions in a reaction affects the rate.

- increase in concentration= increase in

number of molecules that can collide

Conclusion

- increase in temperature= increase in kinetic

energy

- increase in surface area= more molecules

that can readily react

● A catalyst helps increase the rate of a reaction by lowering the activation energy

Recommendation

use other substances that can further prove the factors that affect the reaction rate

Biggest problem: the precision of measurement of the substances used

- watch these values (it can affect the result of the experiment)

References

Brown, T. L., LeMay, H. E., Bursten, B. E., & Murphy, C. (2009). Chemistry, the central science. (11th ed.). Upper Saddle River: Prentice Hall.

Chang, R. (2005). Chemistry. (8th ed.). Singapore: McGraw Hill Inc.