Factors Affecting Reaction Rate

International Baccalaureate Chemistry

Pirathap Loganathan

SCH4U

Lab #2 – Factors Affecting Reaction Rate

By: Pirathap Loganathan

SCH4U – 2

Ms. Amanda Thorne

Friday, October 24, 2008

PART A – BACKGROUND INFORMATION

Chemical reactions occur at different rates. In this experiment, we considered some of the key factors that affect reaction rate:

particle size
temperature
concentration
catalysts

The effect particle size (nature of reactants) has on the rate of a chemical reaction is by how readily bonds are broken and formed, the different phases of the reacting particles and the amount of exposed surface area. The temperature of the system also affects reaction rate. When temperature is increased, particles move faster (more kinetic energy) as there is being more frequent collisions taking pace, and thus an increase in rate. Changes in concentration also plays a role in increasing the rate of a reaction; increased concentration results in more packed particles in the same space, therefore more collisions occur producing a faster reaction rate. Concentration usually increases reaction rate if the reactant are not all in the same phase as well. Lastly, catalysts speed up the rate of a reaction by promoting proper orientation between reacting particles (which will be later discussed along with collision theory) (Helmenstine, 2008).

A model used to describe the observed characteristics of reaction rate, the collision theory provides us with a basis to why chemical reactions occur at different rates at a molecular level, and how it alters the speed of a reaction. The collision theory states that molecules must collide in order to produce a chemical reaction. More frequent the collisions are between reacting particles, the faster the rate of the reaction (Lawson, 2006).

Particles that react often collide without reacting. There two requirements that are necessary for collisions to be effective. In order to produce a chemical reaction, the particles must collide with enough threshold energy (activation energy). The collision energy must equal or exceed the activation energy, the minimum amount of energy required for particles to collide successfully. The particles must also collide with the proper molecular orientation of the reactants to allow formation of any new bonds necessary to produce products (Zumdahl, 2007). The purpose of conducting this lab to is to examine factors that influence the rate of a reaction to increase how often collisions occur or by making them more effective.

PART B – OBSERVATIONS AND DATA TABLES

RESULTS

Table 1. Effect of Particle Size on Reaction Rate

Table 2. Effect of Temperature

Table 3. Effect of Concentration

Table 4. Effect of Concentration

PART C – CONCLUSIONS

In part 1 of the lab, we used powdered calcium carbonate and solid marble chips to examine and demonstrate the effect of particle size on reaction rate. We obtained samples of both substances, roughly the same mass, and placed them into two separate test tubes on the test tube rack. We then ...

This is a preview of the whole essay

PART B – OBSERVATIONS AND DATA TABLES

RESULTS

Table 1. Effect of Particle Size on Reaction Rate

Table 2. Effect of Temperature

Table 3. Effect of Concentration

Table 4. Effect of Concentration

PART C – CONCLUSIONS

CaCo3 + HCl → CaCl2 + H2CO3

We observed that gas evolved at a rapid rate from the test tube containing powdered calcium carbonate and reacted at a slower rate with the test tube containing the solid marble chips (Refer to Table 1.). This phenomena is explained by the collision theory. The effect particle size is directly dependent on the amount of exposed surface area and the state the reacting particles are in. In the test tube containing the powdered calcium carbonate, the rate of the reaction was much more quicker than that of the one with solid marble chips because the size of the particles is much smaller, resulting in a greater surface area for collisions to take place. The more frequent the collisions are, the faster the rate of the reaction is. Also, the reaction rate could have also increased due to the bonds breaking and forming and the nature of the reaction itself (Helmenstine, 2008).

In part 2, we determined the effect of temperature had on the rate of a reaction. We filled three 250-mL beakers with water; one with several ice cubes, a second with water at room temperature and a third containing water heated to about 60°C. We then preceded to add an Alka Seltzer tablet to each, and recorded the time it takes for the Alka Seltzer to completely dissolve. We can confirm, from our findings (See Table 2.) that chemical reactions speed up when the temperature is increased. When temperature is increased, more kinetic energy is expended into the system resulting in more particles colliding with each other much faster – increasing the rate. This was shown on all three beakers; virtually all rate constants confirm an exponential increase with absolute temperature. We can conclude that reaction rates are greater at higher temperatures. Conversely, the reverse is true for reactions in lower temperature. The number of collisions is fewer since the particles are moving much more slower (Lawson, 2006).

To determine the effect of concentration has on reaction rate, part 3, we poured 5 mL of three HCl solutions (1, 3 and 6 M HCl respectively) into three different test tubes and placed them on the test tube rack. We then added one piece of magnesium to each test tube and recorded the time until the reaction stopped for each test tube.

Mg + 2 HCl → MgCl2 + H2

What we observed (Refer to Table 3.) was that gas evolved extremely rapidly from the reaction in the test tube containing 6 M HCl. This again supports the collision model; higher the concentration of a reactant, the faster the rate of a reaction will be. This is due to more packed particles occupying the same space, therefore increasing the frequency of collisions – producing an extremely rapid reaction rate. Concentration usually increases reaction rate if the reactant are not all in the same phase as well. A distinct smell/odour was also produced in the reaction (Zumdahl, 2007).

In our final experiment in the lab, part 4, we determined and which substance/substances act as a catalyst for the decomposition of hydrogen peroxide and investigated the effect catalysts on the rate of a reaction. We first diluted the hydrogen peroxide by adding 10 mL of 3% H2O2 to a 100-mL graduated cylinder and followed by adding 90 mL of distilled water to get 100 mL of dilute (hydrogen peroxide). We then rinsed out our 10-mL graduated cylinder and 7 test tubes with this solution (and poured them away) and then placed 5-mL of the diluted hydrogen peroxide into each of the 7 test tubes. Finally, we added 5 drops of each of the 7 solutions (See Table 4.) to separate test tubes.

2 H2O2 → 2 H2O + O2

If the addition of the solid form of each chemical increase the rate of the reaction, we answered “Yes” (meaning it was a catalyst) and “No” if it was not a catalyst. According to our findings, three of the substances were possible catalysts. Catalysts speeds up reaction rate by increasing the number of collision sites between the reactants, and promoting proper orientation between reacting particles (reducing intramolecular bonding between reactants). This, in turn, increases the rate of the reaction. It is also important to note that catalysts do not get consumed in the reaction itself. They are especially useless when a particular reaction does not occur fast enough at normal temperatures. Catalysts also lower the activation energy, providing an alternate pathway for more particles to react and for the reaction to occur (i.e. platinum catalyzing the combustion of hydrogen and oxygen at room temperature) (2005).

REFERENCES

Lawson, Peggy (2006, May 22). Chemistry 30 chemical kinetics index. Retrieved October 24, 2008, from Chemistry 30 – Saskatchewan Learning Web site: http://www.saskschools.ca/curr_content/chem30_05/2_kinetics/kinetics_index.htm

Factors affecting reaction rates. Retrieved October 24, 2008, from ThinkQuest Web site: http://library.thinkquest.org/C006669/data/Chem/kinetics/factors.html

(2005). Rates of reaction and collision theory. Retrieved October 24, 2008, from Sciencepages.co.uk Web Site: http://www.sciencepages.co.uk/keystage4/GCSEChemistry/m3ratesofreaction.php

Helmenstine, Anne M. (2008). Factors that affect the chemical reaction rate. Retrieved October 24, 2008, from About.com Web site: http://chemistry.about.com/od/stoichiometry/a/reactionrate.htm

(2008, October 23). Reaction rate. Retrieved October 24, 2008, from Wikipedia Web site: http://en.wikipedia.org/wiki/Reaction_rate

Zumdahl, Steven S. & A. Zumdahl (2007). Chemistry: Seventh edition. Boston, MA: Houghton Mifflin Company.

Factors Affecting Reaction Rate