Advertisements
Advertisements
प्रश्न
Answer the following question.
Obtain the relation between ΔG and `triangle "S"_"total"`. Comment on the spontaneity of the reaction.
Advertisements
उत्तर
1) The total entropy change that accompanies a process is given by,
`triangle "S"_"total" = triangle "S"_"sys" + triangle "S"_"surr"`
OR
`triangle "S"_"total" = triangle "S" + triangle "S"_"surr"` ....(1)
2) According to second law of thermodynamics for a process to be spontaneous, `triangle "S"_"total"` > 0.
3) If ∆H is the enthalpy change accompanying a reaction (system), the enthalpy change of the surroundings is –∆H. Thus,
`triangle "S"_"surr" = - (triangle "H")/"T"` ....(2)
4) Substituting equation (2) in equation (1), we get,
`triangle "S"_"total" = triangle "S" - (triangle "H")/"T"`
Rearranging above expression, we get,
`"T" triangle "S"_"total" = "T" triangle "S" - triangle "H"`
or
`- "T" triangle "S"_"total" = triangle "H" - "T" triangle "S"` .....(3)
5) The change in Gibbs energy at constant temperature and constant pressure is given by,
∆G = ∆H - T ∆S …(4)
6) Substituting equation (3) in equation (4), we get,
∆G = `- "T" triangle "S"_"total"`
7) For a spontaneous reaction, `"S"_"total"` > 0 and hence, ∆G < 0. At constant temperature and pressure Gibbs energy of the system decreases in a spontaneous process.
8) The second law leads to the conditions of spontaneity as follows:
i) `triangle "S"_"total"` > 0 and ∆G < 0, the process is spontaneous.
ii) `triangle "S"_"total"` < 0 and ∆G > 0, the process is nonspontaneous.
iii) `triangle "S"_"total"` = 0 and ∆G = 0, the process is at equilibrium.
APPEARS IN
संबंधित प्रश्न
In which of the following, entropy of the system decreases?
Answer the following in one or two sentences.
State second law of thermodynamics in terms of entropy.
Answer the following in one or two sentences.
Comment on the spontaneity of reactions for which ∆H is positive and ∆S is negative.
Obtain the relationship between ∆G° of a reaction and the equilibrium constant.
Answer in brief.
What is entropy? Give its units.
One mole of NaCl(s) on melting absorbed 30.5 kJ of heat and its entropy increased by 28.8 J K−1. The melting point of NaCl is ____________.
For a reversible spontaneous change, ∆S is ____________.
Arrange the following in order of increasing entropy.
I. 1.0 mol H2O (298 K, 1 atm)
II. 1.0 mol H2O (270 K, 1 atm)
III. 1.0 mol H2O (400 K, 1 atm)
Which one of the following has ΔS0 greater than zero?
Equilibrium constant for a reaction is 20. What is the value of ∆G0 at 300 K? (R = 8 × 10−3 kJ)
At what temperature, a chemical reaction will have the following values of ∆G, ∆S and ∆H?
∆G = −5.2 KJ mol−1, ∆H = 145.6 kJ mol−1, ∆S = −216 kJ mol−1
For a reaction to be non-spontaneous at all temperatures, values of ΔH and ΔS respectively are ____________.
If ΔH° and ΔS° for the reaction \[\ce{N2O_{4(g)} -> 2NO_{2(g)}}\] is 57.24 kJ and 175.8 JK-1 mol-1 respectively. What is the value of ΔG° for this reaction at 298 K?
Which of following is residual entropy of a substance?
The H-H bond energy is 430 kJ mol-1 and Cl-Cl bond energy is 240 kJ mol-1. ΔfH for HCl is - 90 kJ, then H-Cl bond energy is ______.
The equilibrium constant for a reaction is 10, value of ΔG° at 300 K is (R = 8 × 10-3 kJ)
For a reaction ΔH = - 30kJ and ΔS = - 45 JK-1, at what temperature reaction changes from spontaneous to non-spontaneous?
Relation between ΔH and ΔU for the reaction, \[\ce{2SO_{3(g)} -> 2SO_{2(g)} + O_{2(g)}}\] is _______.
Identify the unit used for measurement of energy according to international system of units?
In which of the following reaction the value of Kp will be equal to Kc?
Write the correct condition for spontaneity in terms of Gibbs energy.
Write the relationship between Gibbs energy change for a process and total entropy change of system and surroundings.
ΔH for the reaction is − 110 kJ, and ΔS is + 40 JK−1 at 400 K. The free energy change for the reaction is ______.
Find out the value of equilibrium constant for the following reaction at 298 K, \[\ce{2NH3_{(g)} + CO2_{(g)} ⇌ NH2 - COONH2_{(aq)} + H2O_{(l)}}\] Gibbs Standard energy change 298 K = –13.6 kJ mol−1.
The entropy of vaporisation of benzene is 85 J K−1 mol−1. When 117 g of benzene vaporises at its boiling point, what is the entropy change of the surroundings if the process is at equilibrium?
Change in Gibbs energy for a certain reaction at 300 K is –24 kJ and change in enthalpy is –16 kJ. What is the entropy change of the reaction?
