Free Energy of Reaction -- Temperature Dependence?
1000°C
-------->
Pt - Rh
2HCN(g) + 6H2O(g)
The above reaction is used in the industrial production of hydrogen cyanide. Consider the relevant thermodynamic data from the appendices of your text. (The tabulated values ΔH°f and S° are for 25°C. For the purposes of this question assume that ΔH° and ΔS° are invariant with temperature. This is not actually true but would generally be a reasonable approximation over "small" temperature ranges.)
a. Calculate ΔH° for this equation.
b. Calculate ΔS° for this equation.
c. Calculate ΔG° at 161°C, for this equation.
Answer:
Below is some data from a program, Chem Eq, provided by Stanley Sandler (authored a text on Thermo). It calculated H and G for you (use these to get S, pretty easy). Temps are in Kelvin. You might want to get this program (DOS based and free) for these types of problems. It's very easy to use.
REACTION DATA
-------------
Name Stoichiometric coefficient
------------ --------------------------
CH4 -2.0000
H2O(g) 6.0000
HCN(g) 2.0000
NH3 -2.0000
O2 -3.0000
GRXN[T=25C, kJ] HRXN[T=25C, kJ] K LN(K[T=25C]) LOG10(K[T=25C])
-9.8820E+02 -9.3940E+02 >10^38 0.399E+03 0.173E+03
CPA CPB CPC CPD CPE
7.5130D+01 -1.1565D-01 1.773D-05 9.8910D-09 0.000D+00
T[K] LN(K) LOG10(K) K GRXN (kJ) HRXN(kJ)
298.00 0.3988D+03 0.1732E+03 >10^38 -9.8818D+02 -9.3941D+02
434.00 0.2803D+03 0.1217E+03 >10^38 -1.0115D+03 -9.3455D+02
1273.00 0.1101D+03 0.4783E+02 >10^38 -1.1657D+03 -9.3622D+02
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