Consider the reaction : H2S(g) + \(\tfrac{3}{2}\) O2(g) → SO2(g) + H2O(g), ΔH° = 518.62 kJ What is the effect of increase of temperature and pressure on the reaction ?
Retardation and advancement of reaction, respectively
Le Chatelier's principle is applied twice, once for each change.
Effect of pressure. Count the gas moles on each side: \(1 + \tfrac{3}{2} = 2.5\) on the left against \(1 + 1 = 2\) on the right. The reaction proceeds with a decrease in the number of gas molecules, so raising the pressure shifts the equilibrium forward — an advancement.
Effect of temperature. The combustion of hydrogen sulphide is strongly exothermic; heat is a product. Raising the temperature therefore pushes the equilibrium backward — a retardation.
So on the chemically correct reading the answer is retardation with increasing temperature and advancement with increasing pressure.
The difficulty is that the stem prints \(\Delta H^{\circ} = +518.62\) kJ, a positive value, which would make the reaction endothermic. Taken literally that sign would reverse the temperature argument and give advancement in both cases. But the combustion of H2S to SO2 and water is unambiguously exothermic — the standard value is close to \(-518\) kJ mol-1 — so the printed sign is almost certainly a misprint for \(-518.62\) kJ.
It is worth noting that pressure affects the position of equilibrium here only because \(\Delta n_{gas} \ne 0\); had the moles balanced, pressure would have had no effect at all.
Note: the SPPU final answer key marked this question with code 9 ("No option is correct or the question is wrong"), consistent with the contradictory enthalpy sign. The answer recorded here follows the chemically correct exothermic reading and is flagged as key-disputed.
Similar Questions
The property measured in derivative thermogravimetric analysis (DTG) is :
Analysis of four different samples of an alloy yielded 12.12, 12.14, 12.10 and 12.22% of metal. The mean deviation of the result is :
For the first order consecutive reaction :
Which of the following statement is incorrect ?
A given reaction is fitted into the following Arrhenius form :
K2 = 6.0 × 1014 (S-1) . exp \(\left[-\frac{104.4\ (\mathrm{kJ\,mol^{-1}})}{RT}\right]\)
Value of the rate constant at very high temperature would be :
E° value for various ions are as follows :
E°(MnO4-) = +1.51 V
E°(Ag/Ag+) = +0.7996 V
E°(Au/Au+) = +1.692 V
E°(Zn/Zn2+) = -0.761 V
Based on this data, permaganate can be used to oxidize :
Vapour pressure of 0.5 molal solution of non-volatile solute in organic solvent at 30°C would be :
(Given : vapour pressure of pure organic solvent is 100 torr; the molecular weight of organic solvent is 100 g mol-1).
The following half cell represents, normal hydrogen electrode (NHE) :
If, we discharge the electrochemical cell rapidly, then :
The number of microstates of distributing five quanta of energy among four distinguishable particles is :
The variation of Cp with pressure at constant temperature is given by :
Important Questions from Thermodynamics
- Second law of thermodynamics states that
A. Energy flows from higher concentration to lower concentration.
B. Order becomes disorder during energy transformations.
C. The quality of energy degrades as it is transformed.
D. Degraded energy is entropy, dessipated as waste products or heat.
E. Enthalpy is wasted in energy transformation.
Choose the most appropriate answer from the options given below: Choose the Incorrect Statement:
1 For a system at equilibrium, chemical potential is same in all phases.
2 Gibb's free energy change is zero at equilibrium state of a system.
3 Gibb's free energy change is positive for reaction to occur spontaneously.
4 $\Delta G$ will become more negative with increasing temperature.- In a closed thermodynamic system, across its boundaries
Melting Point of pure ice is-
Which one among the following statements with reference to the properties of water is not correct?
