Question Video: Calculating the Standard Heat of Reaction for the Combustion of Methane Using Standard Enthalpies of Formation | Nagwa Question Video: Calculating the Standard Heat of Reaction for the Combustion of Methane Using Standard Enthalpies of Formation | Nagwa

# Question Video: Calculating the Standard Heat of Reaction for the Combustion of Methane Using Standard Enthalpies of Formation Chemistry • First Year of Secondary School

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Methane reacts with oxygen to produce carbon dioxide and water according to the following equation. CH₄ (g) + 2 O₂ (g) ⟶ CO₂ (g) + 2 H₂O (g). Using the data in the table provided, what is the standard heat of reaction, Δ𝐻_(𝑟)^(⦵)? Give your answer to the nearest whole number.

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### Video Transcript

Methane reacts with oxygen to produce carbon dioxide and water according to the following equation. CH4 gas plus two O2 gas react to form CO2 gas plus two H2O gas. Using the data in the table provided, what is the standard heat of reaction, Δ𝐻𝑟? Give your answer to the nearest whole number.

In this question, we need to determine the standard heat of reaction for the reaction between methane and oxygen gas. During a chemical reaction, bonds are broken in the reactants and new bonds are made to form the products. The chemical potential energy of the reactants and products is different. This change in energy in a system is called an enthalpy change and is represented by the symbol Δ𝐻. Putting a ⦵ next to Δ𝐻 indicates measurements are made under conditions of standard temperature and pressure and when reactants and products are in their standard states.

The values provided in the data table are the standard enthalpies of formation for methane, carbon dioxide, and water. The standard enthalpy of formation is the enthalpy change when one mole of substance is formed from its constituent elements in their standard states under standard conditions. Oxygen gas has not been included in the table, because the enthalpy of formation of an element in its standard state is zero.

Now, let’s clear some space to calculate the standard heat of reaction. The standard heat of reaction can be calculated by finding the difference between the sums of the enthalpies of formation for reactants and products. Let’s rewrite this equation to include the identities of the reactants and products. So, we can see that to calculate the heat of reaction, we need to add together the enthalpies of formation of carbon dioxide and water and subtract the sum of the enthalpies of formation of methane and oxygen.

Now we’re ready to substitute the values provided in the table into our equation. The enthalpy of formation of carbon dioxide is negative 393.5 kilojoules per mole, and the enthalpy of formation of water is negative 241.8 kilojoules per mole. However, in the chemical equation, we can see that water has a coefficient of two. Therefore, we must multiply the standard enthalpy of formation of water by two. As for the reactants, the enthalpy of formation of methane is negative 74.86 kilojoules per mole, and for oxygen it is zero kilojoules per mole. After simplification, we get negative 877.1 kilojoules per mole minus negative 74.86 kilojoules per mole. After subtracting, we get negative 802.24 kilojoules per mole. After rounding our answer to the nearest whole number, we get negative 802 kilojoules per mole.

In conclusion, the standard heat of reaction for the reaction between methane and oxygen gas is negative 802 kilojoules per mole.

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