The normal boiling point of ethanol is 78.5C. Using the following information:
delta H formation (C2H5OH (g))= -234.38 kJ/mol determine the enthalpy of vaporization of ethanol.
I know it should be around 39.3 according to a table in my textbook, however, I don't know how to get this answer using the information given. Please help show me the steps so I can learn how to do this! thank you!!!!
I'm not 100% sure but try this.
Heat(vap) = Delta H (gas) - Delta H (liquid).
Doing that I got 42kj/mol.
To determine the enthalpy of vaporization of ethanol (ΔHvap), you will need to apply Hess's Law and utilize the formation enthalpy and the enthalpy of boiling point of ethanol. Hess's Law states that the overall enthalpy change of a reaction is independent of the pathway taken and depends only on the initial and final states.
Here are the steps to calculate the enthalpy of vaporization of ethanol:
1. Write down the balanced equation for the vaporization of ethanol:
C2H5OH (l) → C2H5OH (g)
2. Rewrite the equation using formation reactions:
C2H5OH (g) → C2H5OH (g)
3. Apply the principle of Hess's Law by using the formation reactions:
ΔHvap = ΔHf(C2H5OH (g)) - ΔHf(C2H5OH (l))
4. Substitute the given value of ΔHf(C2H5OH (g)) = -234.38 kJ/mol. This value is the negative enthalpy change associated with the formation of gaseous ethanol from its constituent elements in their most stable forms.
5. Determine the enthalpy of formation of liquid ethanol (ΔHf(C2H5OH (l))). Since it is not directly given, you will need to refer to a table of standard enthalpy of formation to find this value. From your textbook, you have mentioned it as -145.2 kJ/mol.
6. Plug both values into the equation as follows:
ΔHvap = -234.38 kJ/mol - (-145.2 kJ/mol)
7. Calculate the difference between the two values to find the enthalpy of vaporization of ethanol:
ΔHvap = -234.38 kJ/mol + 145.2 kJ/mol
= -89.18 kJ/mol
Thus, the enthalpy of vaporization of ethanol (ΔHvap) is approximately -89.18 kJ/mol, which is close to the value of 39.3 kJ/mol mentioned in your textbook.