
To find:
a) What is the standard heat of combustion of acetylene, where
b) What is the fuel value of acetylene, assuming the products are

Answer to Problem 9.111QA
Solution:
a) The standard heat of combustion of acetylene is
b) The fuel value of acetylene is
Explanation of Solution
1) Concept:
Heat of combustion: The amount of energy released in the form of heat when the compound undergoes complete combustion in the presence of oxygen under standard condition.
For a balanced chemical equation, the standard heat of reaction is the sum of the ∆H0f values of the products, each multiplied by its coefficient describing the reaction, and then subtracting the sum of the ∆H0f values of the reactants, each multiplied by its coefficient.
Fuel value is the amount of energy generated by complete combustion of one gram of fuel
This can be calculated from the enthalpy change for combustion reaction.
2) Formula:
where,
3) Given:
4) Calculation:
a) Heat of combustion of acetylene:
Equation for combustion of acetylene is
Taking an inventory of an atoms on both sides,
The H are already balanced.
To balance the C, we need to add the coefficient 2 in front of
Taking an inventory of atoms on both sides,
To balance the O, we need to add the coefficient
To convert the fractional coefficient to whole numbers, we need to multiply each coefficient by 2.
This is a balanced equation.
From appendix 4, the
Substances | ||||
+226.7 | 0.0 | -393.5 | -241.8 |
Inserting
chemical equation into the formula,
This is the heat of reaction for 2 moles of acetylene.
Standard heat of combustion is expressed in units of
So, standard heat of combustion of acetylene is
Thus, the standard heat of combustion of acetylene is
b) Fuel value of acetylene:
Heat of combustion of
So, the mass of 1 mol of
Therefore, the fuel value of
Conclusion:
Heat of combustion is calculated using the standard heat of formation, and then fuel value is calculated.
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Chapter 9 Solutions
Chemistry: An Atoms-Focused Approach
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