Please explain.
The enthalpy changes for two different hydrogenation reactions of C2H2 are:
C2H2+H2---->C2H4 Delta H 1
C2H2+2H2---->C2H6 Delta H 2
Which expression represents the enthalpy change for the reaction below?
C2H4+H2---->C2H6 Delta H = ?
A. Delta H 1 + Delta H 2
B. Delta H 1 - Delta H 2
C. Delta H 2 - Delta H 1
D. -Delta H 1- Delta H 2
Reverse H1 (make - dH) and add to H2.
To determine the enthalpy change for the reaction C2H4+H2->C2H6, we can use the enthalpy changes of the given hydrogenation reactions:
C2H2+H2->C2H4 ΔH1
C2H2+2H2->C2H6 ΔH2
Looking at the reaction we want to find the enthalpy change for, we can see that it involves the formation of C2H6, which is present in the second hydrogenation reaction. Therefore, the enthalpy change for the reaction C2H4+H2->C2H6 is equal to the enthalpy change of the second hydrogenation reaction ΔH2.
So, the correct expression representing the enthalpy change for the reaction C2H4+H2->C2H6 is:
C. ΔH2 - ΔH1
To find the enthalpy change for the reaction C2H4 + H2 -> C2H6, we need to use the given enthalpy changes for the hydrogenation reactions of C2H2.
First, let's analyze the stoichiometry of the reactions. In the first reaction, 1 mole of C2H2 reacts with 1 mole of H2 to form 1 mole of C2H4. In the second reaction, 1 mole of C2H2 reacts with 2 moles of H2 to form 1 mole of C2H6.
Now, let's consider what we want to find: the enthalpy change for the reaction C2H4 + H2 -> C2H6. We can think of this reaction as a combination of the first and second reactions. We need to adjust the stoichiometry of the given reactions so that we have the same number of moles of C2H4 and C2H6. We can achieve this by multiplying the first reaction by 2:
2(C2H2 + H2 -> C2H4) -> 2C2H4 + 2H2
Now, we have 2 moles of C2H4 and 2 moles of H2 in our adjusted reaction.
Since the enthalpy change is an extensive property, we can use Hess's Law to determine the enthalpy change of the adjusted reaction. According to Hess's Law, the enthalpy change of a reaction is equal to the sum of the enthalpy changes of the individual reactions that make up the overall reaction.
Therefore, the enthalpy change for the reaction C2H4 + H2 -> C2H6 is the sum of the two enthalpy changes: Delta H_1 + Delta H_2.
Thus, the correct expression representing the enthalpy change for the reaction C2H4 + H2 -> C2H6 is:
A. Delta H_1 + Delta H_2