Balancing more complex chemical equations | Chemical reactions | High school chemistry |Khan Academy

Khan Academy

19 Nov 201404:36

EducationalLearning

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TLDRThe video script offers a step-by-step guide on balancing a complex chemical equation involving the combustion of ethylene. It emphasizes starting with complex molecules and saving single element molecules for last to avoid confusion. The narrator demonstrates how to balance carbons, hydrogens, and oxygens, achieving a balanced equation for the reaction of ethylene with oxygen to produce carbon dioxide and water.

Takeaways

🔍 The script discusses the process of balancing a chemical equation, specifically for a combustion reaction involving ethylene and oxygen.
🔥 The reaction described is a combustion reaction where ethylene (C2H4) burns in the presence of oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
🌡 The reaction requires an initial input of energy to start but releases energy once it is underway.
🧪 The script emphasizes the importance of balancing the number of atoms of each element on both sides of the equation to maintain the law of conservation of mass.
🎨 A strategy for balancing complex chemical equations is suggested: start with molecules that contain multiple elements and leave single-element molecules for last.
🔄 The script illustrates the process of balancing the carbon atoms first by adjusting the number of carbon dioxide molecules to match the carbon atoms in ethylene.
💧 Hydrogen atoms are balanced next by determining the correct number of water molecules needed to match the hydrogen atoms in ethylene.
🌀 The oxygen atoms are addressed last, as they are present in both the ethylene, dioxygen, and water molecules, making their balance more complex.
📈 After balancing carbon and hydrogen, the script shows how to count and adjust the oxygen molecules to ensure there are an equal number of oxygen atoms on both sides of the equation.
📝 The final balanced equation is achieved by placing the correct coefficients in front of the ethylene, dioxygen, carbon dioxide, and water molecules.
📚 The script serves as an educational guide for students learning how to balance chemical equations, particularly for those involving more complex molecules.

Q & A

What is the chemical reaction being described in the script?
-The script describes a combustion reaction of ethylene in the presence of oxygen, producing carbon dioxide and water.
What is ethylene in the context of the script?
-Ethylene is a gaseous hydrocarbon (C2H4) that reacts with oxygen in the combustion reaction.
What are the products of the combustion reaction of ethylene?
-The products of the combustion reaction of ethylene are carbon dioxide (CO2) and water (H2O).
Why is it suggested to balance complex molecules first in a chemical equation?
-Balancing complex molecules first is recommended because it avoids the need to repeatedly adjust multiple elements, which can lead to a confusing and repetitive balancing process.
How is the number of carbon atoms balanced in the given equation?
-The number of carbon atoms is balanced by ensuring there are two carbon dioxide (CO2) molecules on the right-hand side to match the two carbon atoms in ethylene (C2H4) on the left-hand side.
How is the number of hydrogen atoms balanced in the given equation?
-The number of hydrogen atoms is balanced by having two water (H2O) molecules on the right-hand side, providing four hydrogen atoms to match the four hydrogen atoms in ethylene (C2H4) on the left-hand side.
Why are oxygen atoms balanced last in the chemical equation?
-Oxygen atoms are balanced last because adjusting the oxygen molecules (O2) only affects the number of oxygen atoms, making it easier to balance after other elements are already balanced.
How many oxygen molecules (O2) are required to balance the oxygen atoms in the given equation?
-Three oxygen (O2) molecules are required on the left-hand side to provide the six oxygen atoms needed to balance the six oxygen atoms on the right-hand side.
What is the final balanced chemical equation for the combustion of ethylene?
-The final balanced chemical equation is: C2H4 + 3 O2 -> 2 CO2 + 2 H2O.
Why is the combustion reaction described as releasing energy?
-Combustion reactions release energy because they involve the breaking of bonds in reactants and the formation of new bonds in products, which typically releases energy in the form of heat and light.

Outlines

00:00

🔥 Introduction to Balancing Complex Chemical Equations

This paragraph introduces the concept of balancing chemical equations, specifically focusing on a combustion reaction involving ethylene and oxygen. It explains that energy is needed to start the reaction, which then releases energy. The paragraph sets the stage by describing the reactants (gaseous ethylene and dioxygen) and the products (carbon dioxide gas and liquid water), and emphasizes the importance of balancing the number of atoms on both sides of the equation.

🎯 Strategy for Balancing Complex Equations

This section discusses the strategy for balancing chemical equations, particularly those with complex molecules. It advises starting with molecules that contain multiple elements and leaving single element molecules for last. This approach helps avoid repetitive adjustments and simplifies the balancing process.

🧪 Balancing Carbon Atoms

The focus here is on balancing carbon atoms first. The paragraph explains that there are two carbon atoms in the ethylene molecule on the left side, and initially one carbon atom in the carbon dioxide molecule on the right side. By adjusting the number of carbon dioxide molecules to two, the carbons are balanced, with two on each side.

💧 Balancing Hydrogen Atoms

This part explains the process of balancing hydrogen atoms. With four hydrogen atoms in ethylene on the left side and initially two hydrogen atoms in water on the right side, the paragraph suggests balancing by having two water molecules, thereby equating the number of hydrogens on both sides to four.

🌬️ Balancing Oxygen Atoms

In this final section, the focus shifts to balancing oxygen atoms. After adjusting for carbon and hydrogen, the paragraph counts the oxygen atoms on the right side, which total six. To balance this on the left side, three dioxygen molecules are needed, each contributing two oxygen atoms, thus balancing the equation. The paragraph concludes with the successfully balanced combustion reaction.

Mindmap

Keywords

💡Chemical Equation

A chemical equation is a symbolic representation of a chemical reaction, showing the reactants and products along with their respective quantities. In the video's theme, the chemical equation is central to understanding the combustion reaction involving ethylene and oxygen, which is the main focus of the video. The script describes the process of balancing the equation to ensure an equal number of atoms on both sides, illustrating the importance of this concept in chemistry.

💡Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, releasing energy in the form of heat and light. The video script uses the combustion of ethylene as an example to demonstrate how to balance a chemical equation. This reaction is a classic example of a combustion process, emphasizing the release of energy as a key characteristic of such reactions.

💡Ethylene

Ethylene, with the chemical formula C2H4, is a simple hydrocarbon molecule that serves as the starting reactant in the combustion reaction discussed in the video. It is highlighted as a gaseous molecule, which is important for understanding the state of matter in chemical reactions. The script uses ethylene to introduce the concept of balancing complex molecules in a chemical equation.

💡Dioxygen

Dioxygen, or O2, is the most common form of oxygen found in Earth's atmosphere. It is a critical reactant in the combustion reaction featured in the video script. The term is used to describe the oxygen molecule that reacts with ethylene to form carbon dioxide and water, illustrating the role of oxygen in combustion reactions.

💡Carbon Dioxide

Carbon dioxide, with the chemical formula CO2, is a product of the combustion reaction between ethylene and oxygen. The video script discusses the formation of carbon dioxide as one of the outcomes of the reaction, emphasizing the need to balance the number of carbon atoms on both sides of the chemical equation.

💡Water

In the context of the video, water is a product of the combustion reaction, specifically in its liquid form. The script mentions water to illustrate the formation of another product from the reaction, highlighting the need to balance the number of hydrogen and oxygen atoms in the chemical equation.

💡Balancing Chemical Equations

Balancing chemical equations is the process of ensuring that the number of atoms of each element is the same on both sides of the equation, adhering to the law of conservation of mass. The video script provides a step-by-step guide on how to balance the given combustion reaction, emphasizing the importance of this process in accurately representing chemical reactions.

💡Law of Conservation of Mass

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. The video script implicitly references this law when explaining the process of balancing chemical equations, ensuring that the total mass of reactants equals the total mass of products.

💡Gaseous Form

The term 'gaseous form' refers to the state of matter of a substance when it exists as a gas. In the video script, ethylene and dioxygen are both described as being in the gaseous form, which is relevant to the conditions under which the combustion reaction takes place.

💡Energy

Energy is a central concept in the video script, particularly in the context of a combustion reaction, where energy is released. The script mentions that energy is needed to initiate the reaction and also released during the reaction, illustrating the dynamic nature of energy in chemical processes.

💡Molecules with Multiple Elements

The video script advises to balance molecules that contain multiple elements before those with a single element when balancing chemical equations. This strategy is highlighted as a way to simplify the balancing process, as changing the number of complex molecules can have cascading effects on the balance of the equation.

Highlights

Introduction to balancing chemical equations with complex molecules.

Explanation of the combustion reaction involving ethylene and oxygen.

Ethylene is in the gas form (g), and dioxygen is the most prevalent form of oxygen in the atmosphere.

Combustion reaction produces carbon dioxide gas and liquid water, releasing energy.

Goal is to balance the number of each atom on both sides of the equation.

Start by balancing molecules with multiple elements first.

Leave molecules with only one element for last to avoid complex balancing loops.

Begin with balancing the carbon atoms: two carbons on the left, balance by having two carbon dioxide molecules on the right.

Move to balancing the hydrogen atoms: four hydrogens on the left, balance by having two water molecules on the right.

Save balancing the oxygen atoms for last as oxygen is present in multiple molecules.

Count the total number of oxygen atoms on both sides after balancing carbon and hydrogen.

Four oxygens from carbon dioxide and two from water, totaling six oxygens on the right.

Adjust the number of dioxygen molecules on the left to balance the six oxygens needed.

Three dioxygen molecules on the left provide the required six oxygen atoms.

Final balanced equation has equal numbers of each type of atom on both sides.

Transcripts

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