5b. The Standard Molar Enthalpy of Formation (AH° f ) of hydrogen cyanide, (HCN(g)), cannot be determined directly because the compound cannot be prepared by the reaction of hydrogen gas (H2 (g)), carbon (Cs) and nitrogen gas (N2(g)): Eq#0: /2 H2 (9) + Cs) + /2 N2(@) #> HCNG) AH° f = (cannot measure) It can be calculated from the Enthalpies of Reactions (AH° rxn) of the following chemical reactions. The Enthalpies of Reactions (AH° rxn) of these reactions are known: Eq#1: N2 (g) + 3 H2(g) → 2 NH3 (g) ΔΗΟ rxn -91.8 kJ Eq#2: CH4(g) C(graphite) + 2 H2(g) ΔΗΟ rxn +74.9 kJ Eq#3: CH4(g) + NH3 (g) → HCN(9) + 3 H2(g) ΔΗ = +255.9 kJ rxn Use Hess's Law and Equations 1, 2 and 3 to calculate the Enthalpy of Formation (AH;º) of hydrogen cyanide, (HCN(9), as it is written in equation #0: AH [ Select ] kJ/mol (1 mol of HCN9))
5b. The Standard Molar Enthalpy of Formation (AH° f ) of hydrogen cyanide, (HCN(g)), cannot be determined directly because the compound cannot be prepared by the reaction of hydrogen gas (H2 (g)), carbon (Cs) and nitrogen gas (N2(g)): Eq#0: /2 H2 (9) + Cs) + /2 N2(@) #> HCNG) AH° f = (cannot measure) It can be calculated from the Enthalpies of Reactions (AH° rxn) of the following chemical reactions. The Enthalpies of Reactions (AH° rxn) of these reactions are known: Eq#1: N2 (g) + 3 H2(g) → 2 NH3 (g) ΔΗΟ rxn -91.8 kJ Eq#2: CH4(g) C(graphite) + 2 H2(g) ΔΗΟ rxn +74.9 kJ Eq#3: CH4(g) + NH3 (g) → HCN(9) + 3 H2(g) ΔΗ = +255.9 kJ rxn Use Hess's Law and Equations 1, 2 and 3 to calculate the Enthalpy of Formation (AH;º) of hydrogen cyanide, (HCN(9), as it is written in equation #0: AH [ Select ] kJ/mol (1 mol of HCN9))
Chemistry
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Chapter6: Thermochemistry
Section: Chapter Questions
Problem 68E: In a coffee-cup calorimeter, 1.60 g NH4NO3 is mixed with 75.0 g water at an initial temperature of...
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Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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![5b. The Standard Molar Enthalpy of Formation (AH° f ) of hydrogen cyanide, (HCN(g)), cannot be
determined directly because the compound cannot be prepared by the reaction of hydrogen gas (H2
(g), carbon (C(s)) and nitrogen gas (N2(g)):
Eq#0:
/2 H2 (5) + C(s) + /2 N2(g) #> HCN(9)
ΔΗΟ
(cannot measure)
It can be calculated from the Enthalpies of Reactions (AH° rxn) of the following chemical reactions.
The Enthalpies of Reactions (AH° rxn) of these reactions are known:
N2
+ 3 H2(9)
2 NH3 (g)
Eq#1:
(g)
AH°
rxn
-91.8 kJ
Eq#2:
CH4(g)
→ C(graphite) + 2 H2(g)
AH°
rxn
+74.9 kJ
Eq#3:
CH4(9)
NH3 (g)
→ HCN(g) + 3 H2(g)
ΔΗΟ
rxn
= +255.9 kJ
+
Use Hess's Law and Equations 1, 2 and 3 to calculate the Enthalpy of Formation (AHF°) of
hydrogen cyanide, (HCN(9), as it is written in equation #0:
AH
[ Select ]
kJ/mol (1 mol of HCN(g)](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fb99220ad-d702-4943-b904-ec3abe399c73%2F885c0ec1-f84f-40d7-bbd0-cbc10fc802d3%2Fbbkxapf_processed.png&w=3840&q=75)
Transcribed Image Text:5b. The Standard Molar Enthalpy of Formation (AH° f ) of hydrogen cyanide, (HCN(g)), cannot be
determined directly because the compound cannot be prepared by the reaction of hydrogen gas (H2
(g), carbon (C(s)) and nitrogen gas (N2(g)):
Eq#0:
/2 H2 (5) + C(s) + /2 N2(g) #> HCN(9)
ΔΗΟ
(cannot measure)
It can be calculated from the Enthalpies of Reactions (AH° rxn) of the following chemical reactions.
The Enthalpies of Reactions (AH° rxn) of these reactions are known:
N2
+ 3 H2(9)
2 NH3 (g)
Eq#1:
(g)
AH°
rxn
-91.8 kJ
Eq#2:
CH4(g)
→ C(graphite) + 2 H2(g)
AH°
rxn
+74.9 kJ
Eq#3:
CH4(9)
NH3 (g)
→ HCN(g) + 3 H2(g)
ΔΗΟ
rxn
= +255.9 kJ
+
Use Hess's Law and Equations 1, 2 and 3 to calculate the Enthalpy of Formation (AHF°) of
hydrogen cyanide, (HCN(9), as it is written in equation #0:
AH
[ Select ]
kJ/mol (1 mol of HCN(g)
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