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1. Introduction:
Catalysts, a recurring concept in the HL Chemistry syllabus, are known to create
alternative pathways that help speed up reactions. An example is the use of catalysts in the food
industry to “control process time, enrich the flavor, improve texture, increase shelf life, and
decrease the use of chemical food additives” (National Center for Biotechnology Information).
Catalysts are used in many industrial processes and also in keeping organisms alive. Catalysts
play a vital role in everyday human activity, which is why my interest in catalysts was sparked.
To further investigate the role of catalysts, I researched reactions that require catalysts
and came across a common reaction known as the “decomposition of H2O2,” also known as
Hydrogen Peroxide. Hydrogen peroxide is a colorless liquid at room temperature that is highly
unstable and decomposes to oxygen, water and releases heat. Although Hydrogen Peroxide is
nonflammable, it is a powerful oxidizing agent that can cause spontaneous combustion when it
comes in contact with organic material. Hydrogen Peroxide is used throughout the healthcare
industry. It is used as an oxidizing agent and can be found in first-aid antiseptics in order to clean
bacteria and prevent infections. Additionally, Hydrogen Peroxide is found in toothpaste,
mouthwash, and bathroom cleaners, which works as an oxidizing agent offering a lightening and
whitening effect (“Hydrogen Peroxide”).
Furthermore, Hydrogen Peroxide can be found in us humans too. In humans, Hydrogen
Peroxide can primarily be found in three places: the lungs, gut, and thyroid gland. Enzymes, also
known as natural catalysts, are organic catalysts that accelerate chemical reactions in the
human body. Catalase is an enzyme that decomposes Hydrogen peroxide in the human body
before it can form hydroxyl radicals, which can harm the body. This decomposition of Hydrogen
Peroxide with the use of catalase produces water and oxygen, substances harmless to the body.
Subsequently, catalase, an organic catalyst, is not the only substance that can break
down hydrogen peroxide. The decomposition of Hydrogen Peroxide is slow if uncatalyzed.
Therefore, industries use Inorganic catalysts, which are used to break down Hydrogen Peroxide
quicker. Potassium iodide and manganese dioxide are two inorganic chemical compounds that
decompose Hydrogen Peroxide.
This further led me to conceptualize my research question: To what extent do the rate
of reaction differ for the decomposition of hydrogen peroxide in a pH-neutral environment at
the same temperatures when using manganese dioxide, potassium iodide, and catalase
measured by a gas sensor pressure?
2. Background Research:
As previously stated, Hydrogen Peroxide breaks down into water, oxygen and releases
heat. This can be illustrated below:
2H2O2 (aq) → 2H2O (I) + O2 (g) + heat
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Hydrogen Peroxide has a tetrahedral electron geometry and a bent molecular structure.
The structure can be further shown below in figure 1. Hydrogen Peroxide consists of
oxygen-oxygen single bonds and hydrogen-oxygen single bonds. The oxygen bonds tend to
decompose because the oxygen bonds are volatile. The
decomposition of Hydrogen Peroxide is exothermic and has
a high negative Gibbs free energy. The decomposition of
Hydrogen Peroxide is a disproportionation reaction due to
one of the oxygen atoms, in the Hydrogen Peroxide being
reduced from a negative one to negative two and the other
oxygen atom being oxidized from a negative one to zero.
One thing to note is that Hydrogen Peroxide has a shelf life,
meaning that Hydrogen Peroxide degrades no matter the condition. Some conditions that affect
the decomposition of Hydrogen Peroxide are light, temperature, and pH; this is crucial for this
exploration to control some of the conditions. Moving onwards, the catalyst will decrease the
activation energy of hydrogen peroxide by making an alternative pathway. This can also be
illustrated in the Maxwell-Boltzmann distribution, where the lower activation can be shown
below in figure 2:
The catalyzed reaction versus uncatalyzed reaction for hydrogen peroxide can be seen below:
