Concept explainers
Given ΔH° for the reaction
If the heat of combustion of acetylene is
What is the value of
Interpretation:
The heat of hydrogenation of ethylene and of acetylene to ethylene and ethane is to be calculated, and the enthalpy of the given hypothetical reaction is to be calculated.
Concept introduction:
Heat of a reaction can be determined from the measured heats of other reactions.
When a reaction equation is multiplied by some number, each coefficient in the balanced equation along with the associated enthalpy change is multiplied by that number.
If a reaction is reversed, the sign of the associated heat of reaction changes.
Answer to Problem 42P
Solution:
The heat of hydrogenation of ethylene is
Explanation of Solution
The combustion reactions of hydrogen (given), ethane, and ethylene are as follows:
The reaction for the heat of hydrogenation of ethylene is shown below:
Using the above three equations, the heat of reaction for hydrogenation of ethylene is calculated as below:
Add reactions (1) and (3)m and add a reverse reaction (2):
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(Note: Subtracting reaction (2) is the same as reversing and adding it. The final equation is obtained by cancelling out any terms common to both sides of the equation.)
Thus, the heat of hydrogenation of ethylene is
b) The equation for heat of combustion of acetylene is as follows:
The reaction for heat of hydrogenation of acetylene to ethylene is shown below:
———————————————————————————————————–
Thus, the enthalpy change for hydrogenation of acetylene to ethylene is
The equation for heat of combustion of acetylene to is as follows:
The reaction for heat of hydrogenation of acetylene to ethane is shown below:
———————————————————————————————————–
Thus, the enthalpy change for hydrogenation of acetylene to ethane is
c)
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Chapter 2 Solutions
ORGANIC CHEMISTRY-W/STUD.SOLN.MAN.
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