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. 👁 127
asked by Chris
  1. Al(s)+3/2O2(g)-->Al2O3(s)
    delta H=-167.6kj

    1. 👍 0
    2. 👎 0
    posted by Jillian

Respond to this Question

First Name

Your Response

Similar Questions

  1. Chemistry

    Use standards entropies and heats of formation to calculate delta Gf at 25C for a. cadmium (II) chloride (s) b. methyl alcohol, CH3OH (l) c. copper (I) sulfide (s) I really have no idea where to start with this problem. I have no

    asked by Olivia on November 9, 2013
  2. Chemistry II

    The value of ^G for the following reaction is -5490 kJ. Use this value and data to calculate the standard free energy of formation for C4H10 (g). 2 C4H10 (g) + 13 O2 (g) --> 8 CO2 (g) + 10 H2o (l) Do you know the heats of

    asked by Jayd on May 23, 2007
  3. Chemistry

    Calculate the heat of reaction (ΔHrxn) for the following reactions, using heats of formation (ΔHf). Show your work. Refer to a table of heats of formation in your textbook as needed. 5O2(g) + 4NH3(g) → 6H2O(g) + 4NO(g)

    asked by Morgan on March 1, 2015
  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
  5. Chemistry

    Calculate the entropy of formation (J/K mol) of CS2(l). The value of T delta S^0 for the equation as written is -16.7774 KJ/mol. (the given standard entropies are: O2= 205.138, CO2= 213.7, SO2= 248.22) CS2(l) + 3 O2(g) --> CO2(g)

    asked by Anonymous on March 10, 2008
  6. chemistry

    Which of the following equations represents a reaction for which the delta H can be called a standard enthalpy of formation, delta Hf? a) FeO(s) + CO2(g) -> FeCO3(s) b) 1/2 N2(g) + 2 O(g) -> NO2(g) c) 2 Na(s) + Cl2(g) -> 2 NaCl(s)

    asked by timmy on January 23, 2012
  7. chemistry

    I can't figure this question out for the life of me. If anyone could help me, that'd be great! Given change of heat of formation for Cu^2+ (aq)=+71.7kJ/mol and that for Zn^2+(aq)= -153.9kJ/mole; find the heat of reaction for:

    asked by Anonymous on June 24, 2006
  8. chemistry

    Calculate the heat of formation of SiO4(s), given that the heats of formation of SiO2(s), -910.90 KJ/mol; H2O(l), -285.8 KJ/mol; HF (g), -271.1 KJ/mol. I know the heat of formation is products minus reactants but how do i do this

    asked by matt on November 8, 2008
  9. Chemistry

    Consider the isomerization equlibria of an alkene (C4H8) that co-exists as three isomers. (These 3 are in an equlibrium triangle) Reaction 1: cis-2-butene ⇔ trans-2-butene Reaction 2: cis-2-butene ⇔ 2-methylpropene Reaction 3:

    asked by Gleb on March 3, 2013
  10. 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

More Similar Questions