How does a catalyst affect activation energy and reaction rate?

A catalyst is a substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction. Catalysis is the process of adding a catalyst to facilitate a reaction.

During a chemical reaction, the bonds between the atoms in molecules are broken, rearranged, and rebuilt, recombining the atoms into new molecules. Catalysts make this process more efficient by lowering the activation energy, which is the energy barrier that must be surmounted for a chemical reaction to occur. As a result, catalysts make it easier for atoms to break and form chemical bonds to produce new combinations and new substances.

Using catalysts leads to faster, more energy-efficient chemical reactions. Catalysts also have a key property called selectivity, by which they can direct a reaction to increase the amount of desired product and reduce the amount of unwanted byproducts. They can produce entirely new materials with entirely new potential uses.

Over the past several decades, scientists have developed increasingly specialized catalysts for essential real-world applications. In particular, powerful catalysts have transformed the chemical industry. These advances have led to biodegradable plastics, new pharmaceuticals, and environmentally safer fuels and fertilizers.

DOE Office of Science: Contributions to Catalyst Research

The Department of Energy (DOE) Office of Science Basic Energy Sciences program actively supports basic research on catalysts. DOE focuses on the design of new catalysts and on the use of catalysts to control chemical transformations at the molecular and sub-molecular levels. DOE research emphasizes understanding these reactions and how to make them more efficient and targeted. DOE’s overarching goal is to develop new concepts in catalysis and new catalysts to help industry produce fuels and chemicals from fossil and renewable raw materials more efficiently and sustainably. This research is helping advance solar fuels, which are fuels companies make using the sun and common chemicals like carbon dioxide and nitrogen. This research is also creating advanced methods for transforming discarded plastic into new products.

Fast Facts

• Humans have been using catalysts for thousands of years. For example, the yeast we use to make bread contains enzymes, which are natural catalysts that aid the conversion of flour into bread.
• The 2005 Nobel Prize in Chemistry was awarded to three researchers (Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock) for their work on metathesis catalysts. Drs. Grubbs and Schrock were funded in part by DOE for their Nobel-Prize research. Dr. Schrock continues to be funded by DOE.
• The 2018 Nobel Prize in Chemistry was awarded to Frances H. Arnold for her pioneering work to direct the evolution of enzymes for applications such as renewable fuels that are environmentally harmless. She is funded in part by DOE.
• Visit Argonne National Lab for seven more things you may not know about catalysis.

Resources

• DOE Office of Science BES program
• Learn about DOE’s research directions for chemical catalysts.
• Report: Basic Research Needs for Catalysis Science
• How catalysts are transforming the chemical industry, solar fuels, and polymer upcycling.
• Science Highlight: Catalysis Sees the Light
• Science Highlight: Scientists Watch Light Break Down a Model Photocatalyst in Near Real Time

Scientific terms can be confusing. DOE Explains offers straightforward explanations of key words and concepts in fundamental science. It also describes how these concepts apply to the work that the Department of Energy’s Office of Science conducts as it helps the United States excel in research across the scientific spectrum.

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What is a Catalyst? What is Catalysis?

Catalysts are substances that modify the reaction rate and themselves remain chemically and quantitatively unchanged after the reaction. The mechanism by which a catalyst increases the reaction rate is referred to as catalysis.

In this article, we will study what is the meaning of catalyst, how does a catalyst affect the rate of chemical reactions, and also the type of catalysis.

What is a Catalyst in a Chemical Reaction? 

Let’s try to understand this with the help of an example- When potassium chlorate is heated, it readily decomposes to give dioxygen. This decomposition occurs at high temperatures- 653-873K.

2KClO3 → 2KCl + 3O2

When manganese dioxide is added, decomposition takes place at a lower temperature and a much faster rate. The catalyst, manganese dioxide thus accelerates the chemical reaction while itself remaining unchanged throughout the reaction. Here manganese oxide acts as a catalyst.

Hence, this reaction is known as a catalytic reaction.

The mechanism followed by the catalyst is catalysis. There are two types of catalysis- heterogeneous and homogeneous catalysis.

What is Homogeneous Catalysis?

If the reactant and catalysts are in the same phase, they are said to be homogeneous catalysis. 

• The oxidation of sulfur dioxide with dioxygen into sulfur trioxide in the presence of nitrogen oxides as the catalyst.

2SO2(g) + O2(g) → 2SO3(g)

• In the given reaction, both the reactant and catalyst are in the same phase i.e gaseous phase.

What is Heterogeneous Catalysis?

If the reactant and the catalysts are in different phases, they are said to be heterogeneous catalysis.

• Sulfur dioxide oxidized to sulfur trioxide in the presence of Pt.

2SO2(g) → 2SO3

Here the catalyst is in a solid phase while the reactant in the gaseous phase.

• In the presence of nickel as a catalyst, hydrogenation of vegetable oils

Vegetable oils(l) + H2(g) → Vegetable ghee(s)

Here one reactant is in the liquid phase while the catalyst is in a solid phase.

How Does a Catalyst Affect the Rate of Chemical Reactions?

• The reactant molecules must have threshold energy for reactants to react and give a product, and the number of molecules with this energy should also be above the threshold value. Activation Energy is the name of this basic energy. Only those reactant molecules would be able to form products that have energy above the energy of activation.

Now the question is  - ”What do catalyst do?”

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• Catalyst adjusts this activation energy or has a different mechanism of reaction that needs lower activation energy to form products. In intermediate-complex theory, the role of a catalyst in chemical reactions is best explained.

• It brings down the activation energy for a reaction, according to intermediate-complex theory, or offers a separate reaction pathway where activation energy is lower.

• To form an intermediate complex, it makes temporary bonds with the reactant molecules. To provide the components and the catalyst, this intermediate complex then decomposes. Prior to and after the reaction, the catalyst remains the same. No (chemical) changes are found in them.

• A catalyst can only catalyze spontaneous reactions, since it can not modify the Gibbs Free Energy, G, and can thus not catalyze a non-spontaneous reaction.

• It has been noted that for a reaction, a catalyst does not alter the equilibrium constant but rather accelerates backwards as well as the forward reaction to rapidly reach equilibrium. A catalyst catalyzes both the forward and the backward response to the same degree, so the point of equilibrium stays the same and is easily reached compared to the reaction without it.

Do you know?

• Even our body has different kinds of catalysts, which are called enzymes, which play an important role in chemical reactions that occur within our body. 

• Enzymes are complex organic nitrogenous compounds that are provided by plants and animals. They are the protein of high molecular mass molecules and form colloidal solutions in water. 

• They are very powerful catalysts; they catalyze various reactions, particularly numerous reactions. To continue the life process, the bodies of animals and plants are catalyzed by enzymes. The enzymes are thus called biochemical enzymes. The phenomenon and catalysts are known as biochemical catalysis.

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