2. Consider the following reaction and the tabulated thermochemical data at 298 K. 4 NH3(2) + 5 O2(g) → 6 H2O(g) + 4 NO(3) Substance NH3(g) Ozg) H2O(g) NO(2) AH°r (kJ/mol) S° (J/mol-K) -46.1 -241.8 90.3 192.3 205.0 188.7 210.7 A. Calculate the standard enthalpy change of the reaction in kJ. Is the process endothermic or exothermic? B. Calculate the standard entropy change of the reaction in J/K. C. Calculate the standard Gibbs free energy change of the reaction in kJ at 298 K. Is the reaction spontaneous at 298 K?
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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![2. Consider the following reaction and the tabulated thermochemical data at 298 K.
4 NH3(2) + 5 O2(g)
→ 6 H2O(g) + 4 NO(2)
Substance
NH3(g)
Ozg)
H2O(g)
NO(2)
AH°r (kJ/mol)
-46.1
-241.8
90.3
S° (J/mol-K)
192.3
205.0
188.7
210.7
A. Calculate the standard enthalpy change of the reaction in kJ. Is the process endothermic or
exothermic?
B. Calculate the standard entropy change of the reaction in J/K.
C. Calculate the standard Gibbs free energy change of the reaction in kJ at 298 K. Is the reaction
spontaneous at 298 K?
D. Calculate the equilibrium constant at 298 K.
E. Calculate the Gibbs free energy change at 298 K for a mixture containing 2.0 atm NH3(g), 1.0 atm
Oz(g), 1.5 atm H2O(g), and 1.2 atm NO(g).
3. Consider the reaction shown below and the tabulated experimental data on initial rates.
A+B + 2 C →D+E
Table 1. Initial concentrations of reactants and the corresponding rates at 25 °C
Rate (M/s)
[A]; (M)
[B]; (M)
[C]; (M)
0.390
0.10
0.10
0.30
0.130
0.10
0.10
0.10
0.975
0.10
0.25
0.30
0.585
0.15
0.10
0.30
A. Determine the reaction order with respect to A, B, and C.
B. Calculate the average rate constant for the reaction.
C. What is the rate law for the reaction and the overall reaction order?
D. Calculate the activation energy (Ea) for the reaction assuming that the frequency factor (A) is 1.23 x
1010 /M?s.
E. What is the rate constant at 50 °C?](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F54ba17ec-9297-43bf-8bc2-3abf16268b30%2Fee70f31e-03e7-4030-b8c7-36801f23313a%2Fn8fswmc_processed.jpeg&w=3840&q=75)
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