Methane, CH4, can be converted to methanol, which, like ethanol, can be used as a fuel. The energy level diagram shown here presents relationships between energies of the fuels and their oxidation products. Use the information in the diagram to answer the following questions. (The energy terms are per mol-rxn.)
- (a) Which fuel, methanol or methane, yields the most energy per mole when burned?
- (b) Which fuel yields the most energy per gram when burned?
- (c) What is the enthalpy change for the conversion of methane to methanol by reaction with O2(g)?
- (d) Each arrow on the diagram represents a
chemical reaction . Write the equation for the reaction that converts methane to methanol.
(a)
Interpretation:
The fuel that yields the most energy per mole when burned has to be determined
Concept Introduction:
Heat energy required to raise the temperature of 1g of substance by 1K.Energy gained or lost can be calculated using the below equation.
Where, q= energy gained or lost for a given mass of substance (m), C =specific heat capacity,
The standard molar enthalpy of formation is the enthalpy change
Explanation of Solution
From the energy level diagram,
Methane liberates at
Methanol liberates at
So, methane yields most energy per mole when it’s burned.
(b)
Interpretation:
The fuel yields the most energy per gram when burned has to be calculated.
Concept Introduction:
Heat energy required to raise the temperature of 1g of substance by 1K.Energy gained or lost can be calculated using the below equation.
Where, q= energy gained or lost for a given mass of substance (m), C =specific heat capacity,
The standard molar enthalpy of formation is the enthalpy change
Explanation of Solution
The fuel yields the most energy per gram when burned
Molar mass of methane is
For methane=
Molar mass of methanol is
For methanol=
So, the fuel that yields the most energy per gram when burned is methane
(c)
Interpretation:
The enthalpy change for the conversion of methane by reaction with
Concept Introduction:
Heat energy required to raise the temperature of 1g of substance by 1K. Energy gained or lost can be calculated using the below equation.
Where, q= energy gained or lost for a given mass of substance (m), C =specific heat capacity,
The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one gram of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.
Explanation of Solution
From the energy level diagram the values obtained are
Methane liberates at
Methanol liberates at
(d)
Interpretation:
The equation for the reaction that converts methane to methanol has to be identified.
Concept Introduction:
Heat energy required to raise the temperature of 1g of substance by 1K. Energy gained or lost can be calculated using the below equation.
Where, q= energy gained or lost for a given mass of substance (m), C =specific heat capacity,
The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one gram of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.
Explanation of Solution
From the energy level diagram the obtained equation for the conversion of methane to methanol is
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Chapter 5 Solutions
Chemistry & Chemical Reactivity
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