Transcript
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.
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