Chemical Reaction Rates

Chemical Reaction Rates

A chemical reaction occurs when two or more elements or compounds combine chemically. The rate at which reaction occurs is determined by thermodynamic factors and concentration of reacting substances.  When one or both factors increase or decrease, the reaction rate also changes.

Literature Review

In chemistry, reaction rates are used to evaluate how fast chemical compounds are formed under controlled conditions. Two major factors that control reaction rate include temperature and concentration of reactants (Holman and Stone 230). The higher these two variables are, the higher the rate of reaction. Therefore, less time is spent to transform reactants into products. Higher temperature increases the rate of reaction. As explained by Houston, the kinetic energy of reactants’ particles increases with increased temperature, resulting in increased particulate collisions (48). When particles collide more, the reaction is rapid, and it takes a shorter time to complete, contrary to the reaction rate at lower temperatures. In essence, higher temperatures fasten the reaction rate, hence making chemical production more economical.

Hypotheses

1. Increase in temperature will lead to an increased rate of reaction
2. Increase in concentration of reactants will result to increased rate of reaction

Method

Fifty grams of zinc powder were weighed and put into one 250ml volumetric flask. A two-holed cork was used to cover the mouth of the flask. In one hole, a thermometer was inserted through, while the other hole was fitted with a well-graduated syringe. The reactants were heated, while the temperature and volume of gas collected were recorded on a notebook at intervals of one minute.  In the second experiment, 50 grams of zinc powder were weighed and put into three 250ml volumetric flasks. Three one-holed corks fitted with calibrated syringes were used to cover the mouths of the flasks. 1M, 0.5M, and 0.25M, 0.125 HCl were prepared. In the first flask, 1M HCl was added. The volume of collected gas was recorded against time at intervals of one minute. A similar process was repeated with 0.5M HCl and 0.25M HCl. Graphs of temperature and concentration were plotted against the volume of gas collected.

Results

Table 1. A table of temperature and volume of hydrogen gas

Table 2. A table of concentration and volume of hydrogen gas

Graph 1. A graph of temperature against the volume of hydrogen gas

Graph 2. A graph of concentration against the volume of hydrogen gas

Discussion

The zinc powder gradually disappeared as hydrogen gas bubbles and zinc chloride formed. After some time, the gas bubbles subsided because all the acid was used up. At lower temperatures, the reaction took a longer time to complete compared to higher temperatures. This variation in reaction rate was attributed to the increased kinetic energy of particles, which resulted from increased bombardment at higher temperatures. At higher concentrations, the reaction rates were also faster compared to the lower level of hydrochloric acid. This variation was caused by increased particle content in more concentrated acid, unlike in the diluted acid.

Conclusion

In conclusion, the rate of reaction largely depends on the temperature and concentration of reactants. My hypotheses were confirmed when increased temperature resulted in an increased reaction rate. Similarly, it was confirmed that a higher level of hydrochloric acid produced an increased rate of reaction. Therefore, these two factors play a significant role in the determination of how fast or slow a reaction would occur. However, it was assumed that the syringes have no gas initially, which is impossible under ideal conditions. The syringe should be evacuated completely.

References

Holman, John S., and Phil Stone. Chemistry: Teacher Resource Pack. Nelson Thornes, 2002.

Houston, Paul L. Chemical Kinetics and Reaction Dynamics. McGraw-Hill, 2001.