Advertisements
Advertisements
प्रश्न
Answer the following question.
Although ΔS for the formation of two moles of water from H2 and O2 is –327J K–1, it is spontaneous. Explain.
(Given ΔH for the reaction is –572 kJ).
Advertisements
उत्तर
1. For the process to be spontaneous, `triangle "S"_"total" = triangle "S"_"sys" + triangle "S"_"surr" > 0`.
2. For the reaction, 2H2(g) + O2(g) → 2H2O(l), when 2 moles of H2 and 1 mole of O2 gas combine to form 2 moles of liquid water, 572 kJ of heat is released which is received by surroundings at constant pressure (and 298 K).
3. The entropy change of the surroundings is,
`triangle "S"_"surr" = ("Q"_"rev")/"T" = (572 xx 10^3 "J")/(298 "K")` = + 1919 J K-1
4. The total enthalpy change is,
`triangle "S"_"total" = triangle "S"_"sys" + triangle "S"_"surr"`
= - 327 J K-1 + 1919 J K-1
= + 1592 J K-1
5. Since `triangle "S"_"total"` > 0, the reaction is spontaneous at 25 °C.
6. It follows that to decide spontaneity of reactions, we need to consider the entropy of system and its surroundings.
APPEARS IN
संबंधित प्रश्न
Define entropy.
Answer the following in one or two sentences.
If the enthalpy change of a reaction is ∆H how will you calculate the entropy of surroundings?
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 the following question.
Determine whether the following reaction is spontaneous under standard state conditions.
2H2O(l) + O2(g) → 2H2O2(l)
if ΔH° = 196 kJ, ΔS° = –126 J/K, does it have a cross-over temperature?
Equilibrium constant for a reaction is 20. What is the value of ΔG° at 300 K? (R = 8 x 10-3 kJ)
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 ____________.
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 ________.
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)
What is the entropy change (in J K−1 mol−1) when one mole of ice is converted into water at 0°C? (The enthalpy change for the conversion of ice to liquid water is 6.0 kJ mol−1 at 0°C)
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?
Standard molar entropy is ______.
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.
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?
For which of the following reaction, ΔH = ΔU?
When will be change in Gibb's free energy always negative?
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 larger entropy or not. If yes then Why?
He(g) in a volume of 1 L or He(g) in a volume of 5 L both at 25°C.
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?
For a certain reaction ΔH0 is −224 kJ and ΔS0 is −153 J K−1. At what temperature the change over from spontaneous to non-spontaneous will occur?
Calculate ΔG0 for the reaction
\[\ce{CH_{4(g)} + H_{2(g)}-> C2H_{6(g)}}\]
State whether the reaction is spontaneous or not. (Given: KP = 3.358 × 1017, T = 25° C, R = 8.314 × 10−3 kJK−1 moI−1)
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.
Define second law of thermodynamics.
