Problem 39 Explain hydrogenation of ethene ... [FREE SOLUTION]

Chapter 9: Problem 39

Explain hydrogenation of ethene and ethyne.

Short Answer

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Question: Explain the process of hydrogenation and provide step-by-step descriptions of hydrogenation of ethene and ethyne. Answer: Hydrogenation is a chemical reaction in which hydrogen atoms are added to unsaturated compounds such as ethene (alkenes) and ethyne (alkynes). The process requires a catalyst, typically nickel or palladium, and occurs under high pressure and temperature, resulting in more saturated compounds like alkanes. In the hydrogenation of ethene (C_2H_4), the carbon-carbon double bond is broken, and hydrogen atoms are added, ultimately forming ethane (C_2H_6), as represented by the equation C_2H_4 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_6. The hydrogenation of ethyne (C_2H_2) occurs in two steps, first forming ethene (C_2H_4) and then ethane (C_2H_6). The carbon-carbon triple bond in ethyne is broken, and hydrogen atoms are added, as represented by the following equations: 1. C_2H_2 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_4 2. C_2H_4 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_6

Step by step solution

Understanding Hydrogenation

Hydrogenation is a chemical reaction wherein hydrogen atoms are added to the carbon-carbon double or triple bonds of unsaturated compounds, such as ethene (alkenes) and ethyne (alkynes). This process requires a catalyst, typically a finely divided metal like nickel or palladium, and occurs under high pressure and temperatures. The result of hydrogenation is usually the formation of more saturated compounds, such as alkanes.

Hydrogenation of Ethene

Ethene (C_2H_4) is an unsaturated hydrocarbon molecule with one carbon-carbon double bond. Hydrogenation involves breaking the double bond and adding hydrogen atoms to form ethane, which is a saturated hydrocarbon. The process can be outlined as follows: 1. Take ethene (C_2H_4) and hydrogen (H_2) molecules. 2. Introduce a catalyst, usually nickel or palladium. 3. Heat the reactants under increased pressure (around 200 atmospheres and 523 K). The reaction can be represented with this equation: C_2H_4 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_6 At the end of this process, two hydrogen atoms have been added to ethene, forming ethane (C_2H_6), a saturated hydrocarbon.

Hydrogenation of Ethyne

Ethyne (C_2H_2) is also an unsaturated hydrocarbon molecule, but it possesses a carbon-carbon triple bond instead of a double bond as in ethene. Hydrogenation of ethyne occurs in two steps, first to form ethene and then to form ethane. The process can be outlined as follows: 1. Take ethyne (C_2H_2) and hydrogen (H_2) molecules. 2. Introduce a catalyst, usually nickel or palladium. 3. Heat the reactants under increased pressure (around 200 atmospheres and 523 K). The reaction can be presented in two equations, one for forming ethene and one for forming ethane: First step: C_2H_2 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_4 Second step: C_2H_4 + H_2 \xrightarrow[Pd or Ni]{Heat,Pressure} C_2H_6 In the first step, the hydrogenation of ethyne to ethene takes place, breaking one of the carbon-carbon triple bonds and adding hydrogen atoms to form ethene. In the second step, ethene undergoes hydrogenation as described in the previous section, forming ethane (C_2H_6), a saturated hydrocarbon.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Ethene Hydrogenation

In chemistry, ethene hydrogenation is a fascinating process. This chemical reaction involves the addition of hydrogen molecules to ethene, transforming it into a more saturated compound known as ethane. Ethene, also called ethylene, is characterized by a carbon-carbon double bond. Hydrogenation breaks this double bond and bonds the hydrogen atoms to the carbon atoms, resulting in the formation of ethane (C_2H_6). The process typically uses a catalyst, which is a substance that accelerates the reaction without being consumed by it.

For ethene hydrogenation:

The catalyst used is often nickel or palladium.
The reaction requires heat and high pressure to proceed efficiently.

The equation for this reaction is:\[ C_2H_4 + H_2 \xrightarrow[\text{Heat, Pressure}]{\text{Pd or Ni}} C_2H_6 \]After hydrogen is added to ethene, it becomes ethane, a saturated hydrocarbon without any double or triple bonds.

Ethyne Hydrogenation

Ethyne hydrogenation is an intriguing two-step process. Ethyne is a hydrocarbon with a carbon-carbon triple bond and is commonly known as acetylene. The hydrogenation process involves the addition of hydrogen atoms, first converting ethyne into ethene and then into ethane.

During the first step:

Ethyne (C_2H_2) reacts with hydrogen (H_2).
A catalyst such as palladium or nickel is used.

The equation for converting ethyne to ethene is:\[ C_2H_2 + H_2 \xrightarrow[\text{Heat, Pressure}]{\text{Pd or Ni}} C_2H_4 \]After breaking one of the triple bonds to form a double bond and adding hydrogen, ethene is produced.

In the second step:

The ethene formed undergoes further hydrogenation.
Again, a catalyst like nickel or palladium is employed under similar conditions.

This results in the equation:\[ C_2H_4 + H_2 \xrightarrow[\text{Heat, Pressure}]{\text{Pd or Ni}} C_2H_6 \]This second step completely saturates the compound, converting ethene into ethane (C_2H_6), which is a completely saturated hydrocarbon.

Catalysts in Chemistry

In the realm of chemistry, catalysts play a vital role in facilitating chemical reactions. A catalyst is a substance that increases the rate of a reaction without undergoing permanent chemical change. In hydrogenation reactions, catalysts are essential for the transformation of unsaturated hydrocarbons like ethene or ethyne into saturated forms like ethane.

Typical catalysts used in these reactions include metals like nickel, palladium, or platinum. These metals are highly effective because:

They provide a surface for the reactant molecules to adhere to, reducing the activation energy needed for the reaction.
They help in breaking the bonds of hydrogen molecules and the unsaturated hydrocarbons, facilitating the addition of hydrogen atoms.

Catalysts make reactions occurring at industrial scales feasible by significantly reducing the energy and time required. In hydrogenation, the products formed, such as ethane, are needed in various industrial applications, making catalysts indispensable in manufacturing and synthesis processes.

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Explain hydrogenation of ethene and ethyne.

Short Answer

Step by step solution

Understanding Hydrogenation

Hydrogenation of Ethene

Hydrogenation of Ethyne

Key Concepts

Ethene Hydrogenation

Ethyne Hydrogenation

Catalysts in Chemistry

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