# For each of the following reactions. identify another quantity that is equal to δh°rxn. ## 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 . 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) The wrong choices, Enthalpy of formation of  bond energy of  bond energy of 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 bond energy of and bond energy of ### Step 2 of 8 Correct option:- Enthalpy of combustion of Part 1 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 .

### Step 3 of 8

(2) The wrong choices, Enthalpy of combustion of . Enthalpy of formation of  bond energy of 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 . 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 bond energy of .

### Step 4 of 8 The correct option:- bond energy of Part 2 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 .

### Step 5 of 8

(3) The wrong choices, Enthalpy of combustion of . bond energy of . bond energy of 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 . 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 bond energy of and bond energy of ### Step 6 of 8 Correct option:- Enthalpy of formation of Part 3 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) The wrong choices, Enthalpy of combustion of . Enthalpy of formation of  bond energy of 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 . 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 .

### Step 8 of 8 Correct option:- Bond energy of Part 4 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 .

Part 1 Part 2 Part 3 Part 4 