For each of the following reactions. identify another quantity that is equal to δh°rxn.

For each of the following reactions, identify anot

Answer

General guidance

Concepts and reason
Enthalpy is a thermodynamic property of a system which is observed when a system is at constant pressure; the heat released or absorbed is equal to the change in enthalpy(AH). The enthalpy of a reaction depends only on the enthalpy of the initial reactants and the enthalpy of the final products but not on the enthalpy of the intermediate product that may be formed.

Fundamentals

Bond enthalpy:- Bond enthalpy is also known as bond energy, and it is defined as the energy required for breaking the chemical bonds in a molecule. Average molar bond enthalpy can be calculated by dividing the bond enthalpy by the total number of bonds present in a molecule. Enthalpy of combustion:- The energy involved in the combustion of a compound is called enthalpy of combustion. Enthalpy of formation:- The energy required for a compound (from its element) in its stable state is called enthalpy of formation.

Step-by-step

Step 1 of 8

(1) CH, (g)+202(g)
CO2(g)+2H20 (1) The wrong choices, Enthalpy of formation of CO2(g) 4 bond energy of C-H 4X bond energy of C-H

The energy required for a compound (from its element) in its stable state is called enthalpy of formation. The given reaction is not a reaction formation. Therefore, the enthalpy of reaction is not equal to the enthalpy of formation. Bond enthalpy is also known as the bond energy, and it is defined as the energy required for breaking the chemical bonds in a molecule. The given equation does not contain the bond breaking of , therefore the enthalpy of reaction is not equal to the 4 bond energy of C-H and 4X bond energy of C-H

Step 2 of 8

CH, (g)+202(g)
CO2(g)+2H20 (1) Correct option:- Enthalpy of combustion of CH,(g)

Part 1

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CO2(g)
0 4xbond energy of C-H
0-4xbond energy of C-H


In the given reaction, methane is burnt in the presence of oxygen, and forms carbon dioxide and water. This type of reaction is called a combustion reaction. The energy involved in the combustion of a compound is called enthalpy of combustion. Therefore, the enthalpy of the reaction is equal to the enthalpy of combustion of CH,(g).

Step 3 of 8

(2) CH,(g)—*C(g)+4H(g) The wrong choices, Enthalpy of combustion of CH,(g). Enthalpy of formation of C(g) 4X bond energy of C-H

The energy involved in the combustion of a compound is called enthalpy of combustion. The given reaction is not a combustion reaction. Therefore, the enthalpy of the reaction is not equal to the enthalpy of combustion of CH,(g). The energy required for a compound (from its element) in its stable state is called enthalpy of formation. The given reaction is not a reaction formation. Therefore, the enthalpy of the reaction is not equal to the enthalpy of the formation of carbon. The bond enthalpy is also known as the bond energy, and it is defined as the energy required for breaking the chemical bonds in a molecule. The given equation does not contain the bond-making of . Therefore, the enthalpy of the reaction is not equal to the 4X bond energy of C-H.

Step 4 of 8

CH,(g)—*C(g)+4H(g) The correct option:- 4 bond energy of C-H

Part 2

Enthalpy of combustion of CH, (g)
Enthalpy of formation of C(g)
4xbond energy of C-H
0-4xbond energy of C-H


In the given reaction, methane is decomposed and forms carbon and four hydrogen atoms. The reaction includes the breaking of four bonds. So, the energy required for breaking the chemical bonds in a molecule is called bond enthalpy. Therefore, the enthalpy of the reaction is equal to bond energy of C-H.

Step 5 of 8

(3) C(graphite) +2H2(g)
→CH, (g) The wrong choices, Enthalpy of combustion ofCH,(g). bond energy of C-H. 4X bond energy of C-H

The energy involved in the combustion of a compound is called enthalpy of combustion. The given reaction is not a combustion reaction. Therefore, the enthalpy of reaction is not equal to the enthalpy of combustion of CH,(g). Bond enthalpy is also known as bond energy, and it is defined as the energy required for breaking the chemical bonds in a molecule. The given equation does not contain bond breaking of . Therefore, the enthalpy of the reaction is not equal to the 4 bond energy of C-H and 4X bond energy of C-H

Step 6 of 8

C(graphite) +2H2(g)
→CH, (g) Correct option:- Enthalpy of formation of CH,(g)

Part 3

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CH, (g)
0 4xbond energy of C-H
0-4xbond energy of C-H


In the given reaction, methane is formed from the elemental form of carbon and hydrogen. The energy required for a compound from its element in their stable states is called enthalpy of formation. Therefore, the enthalpy of reaction is equal to the enthalpy of formation of

Step 7 of 8

(4) C(g)+4H(g)—
CH,(g) The wrong choices, Enthalpy of combustion of CH,(g). Enthalpy of formation of CO2(g) 4 bond energy of C-H

The energy involved in the combustion of the compound is called enthalpy of combustion. The given reaction is not a combustion reaction. Therefore, the enthalpy of the reaction is not equal to the enthalpy of the combustion of CH,(g). The energy required for a compound from its element in their stable states is called the enthalpy of formation. The given reaction is not a reaction formation. Therefore, the enthalpy of reaction is not equal to the enthalpy of formation. Bond enthalpy is also known as the bond energy, and it is defined as the energy required for breaking the chemical bonds in a molecule. The given equation does not contain bond breaking of . Therefore, the enthalpy of the reaction is not equal to the bond energy of C-H.

Step 8 of 8

C(g)+4H(g)—
CH,(g) Correct option:- Bond energy of C-H

Part 4

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CH, (g)
0 4xbond energy of C-H
0-4xbond energy of C-H


In the given reaction, one carbon atom and one hydrogen atom combine to form methane. So the energy required for making the chemical bonds in a molecule is called bond enthalpy. Therefore, the enthalpy of the reaction is equal to the bond energy of C-H.

Answer

Part 1

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CO2(g)
0 4xbond energy of C-H
0-4xbond energy of C-H

Part 2

Enthalpy of combustion of CH, (g)
Enthalpy of formation of C(g)
4xbond energy of C-H
0-4xbond energy of C-H

Part 3

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CH, (g)
0 4xbond energy of C-H
0-4xbond energy of C-H

Part 4

Enthalpy of combustion of CH, (g)
Enthalpy of formation of CH, (g)
0 4xbond energy of C-H
0-4xbond energy of C-H

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