Chemistry

1. Use standard entropies and heats of formation to calculate delta-G of formation at 25° C for
a) cadmium(II) chloride (s)
b) methyl alcohol, CH3OH (l)
c) copper(I) sulfide (s)

My problem is that I don't know how to calculate delta-G of formation. I know that the Gibbs-Helmholtz equation can take the form
delta-G= delta-H -T(delta-S), but that's not really the same thing, is it? Could I modify the equation so it was all in terms of formation of a substance?

Yes, you can do that but you will need to calculate delta S from Cd, Cl2, and CdCl2. Delta S = S(products)-S(reactants).
Cd + Cl2 ==> CdCl2

I'm still having trouble getting the correct answers. I was able to get the correct one for CdCl2 (344 kJ) but not for the others. The back of my book says CH3OH should be -166.3 kJ, and Cu2S should be -53.6 kJ

Here's my work... maybe you can find where I'm making an error?

CO + 2H2 --> CH3OH
calculating delta-s:
standard molar entropy CH3OH: 126.8 J/K
" " CO: 197.6 J/k
" " H2: 130.6 J/K
-126.8 J/K - (197.6 J/K + 2(130.6 J/K)) = -585.6 J/k
-238.7 kJ (delta-h formation) - 298.2(-.5856 kJ/K) = -154.4 kJ [not correct]

2Cu+1 + S-2 = Cu2S
calculating delta-s
standard molar entropy Cu2S: 120.9 J/k
" " Cu+1: 40.6 J/K
" " S-2: -14.6 J/K

120.9 J/K - (2(20.6 J/K)+ -14.6 J/K)= 54.3 J/K

-79.5 kJ (heat of formation Cu2S) - 298.2(.0543 kJ/K)= -95.69 kJ [not correct]

Where did I go wrong??

My tables don't list CH3OH or inorganic salts so I can't verify any of the other numbers. However, I did verify S for CO and H2. You switched signs from the initial listing of CH3OH delta H as 126.8 from + at the initial listing to - in the calculation. I tried that change and it didn't get 166 either. Have you checked to see if CH3OH is a liquid or a gas? Just as H2O is listed in the tables as a gas and as a liquid, I suspect CH3OH may be too. Look at that. Sorry my tables don't allow me to do any more.

  1. 👍 0
  2. 👎 0
  3. 👁 438
  1. Al(s)+3/2O2(g)-->Al2O3(s)
    delta H=-167.6kj

    1. 👍 0
    2. 👎 0

Respond to this Question

First Name

Your Response

Similar Questions

  1. chemistry

    CH4 + 2O2 ---> CO2 + 2H2O Delta H H2O= -285.8 kJ/mole Delta H CO2= -393.3 kJ/mole What is the standard heat of formation of methane, Delta H CH4, as calculated from the data above

    asked by kc on November 18, 2011
  2. Chemistry II

    C4H4 (g) + 2 H2 (g) --> C4H8 (g) Combustion reactions involve reacting a substance with oxygen. When compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. Using the enthalpies of

    asked by Jayd on May 20, 2007
  3. ap chem

    The heat of combustion of propane is -2,220.1 kJ/mol calculate the heat of formation, delta Hf, of propane given that delta Hf of H20= -285.3 kJ/mol and delta Hf of CO2 = -393.5 kJ/mol

    asked by Anonymous on March 15, 2011
  4. Chemistry

    Given 2Al2O3 (s) --> 4Al(s) + 3O2 (g) (standard enthalpy change= 3351.4 kJ) a) What is the heat of formation of aluminum oxide? How do I find heat of formation from standard enthalpy change? I know how to do it when I'm given

    asked by Chris on January 31, 2007
  1. ap chem

    calculate the lattice enthalpy of potassium fluoride from the following data: enthalpy of formation of K(g): +89 kJ · mol−1 first ionization energy of K(g): +418 kJ · mol−1 enthalpy of formation of F(g): +79 kJ · mol−1

    asked by alexandra on July 13, 2010
  2. Chemistry- college

    The standard enthalpies of formation of ions in aqueous solutions are obtained by arbitrarily assigning a value of zero to H ions;that is, delta H(f) [H+(aq)]=0 A.for this reaction: calculate delta H(f) for the Cl- ions. HCl(g)

    asked by Willy on November 1, 2010
  3. chemistry

    use standard enthalpies of formation to calculate delta Hrxn for the following reaction. 2H2S(g)+3O2(g)-->2H2O(l)+2SO2(g) express the answer using four significant figures Delta Hrxn = ? kJ

    asked by jen on October 25, 2011
  4. Chemistry

    Propane (C3H8) burns according to the following balanced equation: C3H8(g)+5O2(g)→3CO2(g)+4H2O(g) Calculate ΔH∘rxn for this reaction using standard enthalpies of formation. (The standard enthalpy of formation of gaseous

    asked by Anonymous on April 6, 2014
  1. chemistry

    The enthalpy of formation of C2H5OH is -238.7 kJ/mol. What information does this reveal about the bonds in the molecule? A. Bond formation in C2H5OH from its elements only occurs in cold temperatures. B. Bond formation in C2H5OH

    asked by Morgan on December 9, 2014
  2. Chemistry Equations

    What's the equation for the formation of NO2(g) from its elements in its standard states? What's the equation for the formation of BF3(g) from its elements in its standard states? What's the equation for the formation of C2H5OH(l)

    asked by Kyle on November 5, 2009
  3. Chemistry

    Calculate the standard entalphy of formation of naphthalene(C10H8) from the following data: 1) standard enthalphy of combustion of naphtalene is -5153kJ/mol 2) standard enthalphy of formation of CO2 is -393.5kJ/mol 3) standard

    asked by Sarah on March 21, 2018
  4. Chem

    Calculate delta H for the formation of one mole of N2O5 from the elements at 25 degrees C using the following data. 2H2 + O2 - 2H2O delta H = -571.6 kJ N2O5 + H2O - 2HNO3 deltaH = -73.7 kJ 1/2N2 + 3/2O2 + 1/2H2 - HNO3 delta H =

    asked by Anonymous on April 8, 2010

You can view more similar questions or ask a new question.