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
Define entropy.
Answer the following in one or two sentences.
State whether ΔS is positive, negative or zero for the reaction 2H(g) → H2(g). Explain.
Answer the following in one or two sentences.
Comment on the spontaneity of reactions for which ∆H is positive and ∆S is negative.
Equilibrium constant for a reaction is 20. What is the value of ΔG° at 300 K? (R = 8 x 10-3 kJ)
A system is changed from an initial state to a final state by a manner such that ∆H = Q. If the change from initial state to final state was made by a different path, then ____________.
Identify the INCORRECT statement.
For a process, entropy change of a system is expressed as ________.
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)
For the reaction:
\[\ce{2Cl_{(g)} -> Cl2_{(g)}}\]
For the following reaction:
\[\ce{Fe2O3_{(s)} + 3CO_{(g)} -> 2Fe_{(s)} + 3CO2_{(g)}}\]; ΔH0 = −29.8 kJ and ΔS0 = 15 J K−1. What is the value of \[\ce{ΔS_{(total)}}\] at 298 K?
Heat of combustion of C(s), H2(g) and C2H6(g) are −x1, −x2 and −x3 respectively. Hence heat of formation of C2H6(g) is ____________.
Which of the following conditions indicates the reaction is spontaneous?
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 ____________.
Calculate the amount of heat liberated during formation of 2. 7 kg of water if heat of formation of water is - 284.5 kJ mol-1.
For which of the following reaction, ΔH = ΔU?
When will be change in Gibb's free energy always negative?
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?
A reaction is spontaneous at low temperatures but non-spontaneous at high temperatures. Which of the following is true for the reaction?
Standard enthalpy and standard entropy changes for the oxidation of ammonia at 298 K are −382.64 kJ mol−1 and −145.6 JK−1 mol−1, respectively. Standard Gibb's energy change for the same reaction at 298 K is ______.
In which of the following reaction the value of Kp will be equal to Kc?
Identify whether the following pair have a larger entropy or not. If yes then Why?
C2H5OH(l) or C2H5OH(g)
What is a spontaneous process? What are its characteristics?
