NIOS Class 12 Chemistry Chapter 10 Spontaneity of Chemical Reactions Solutions English Medium As Per New Syllabus to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Chemistry Chapter 10 Spontaneity of Chemical Reactions Notes in English and select need one. NIOS Class 12 Chemistry Solutions English Medium Download PDF. NIOS Study Material of Class 12 Chemistry Notes Paper Code: 313.
NIOS Class 12 Chemistry Chapter 10 Spontaneity of Chemical Reactions
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Spontaneity of Chemical Reactions
Chapter: 10
| Module – IV: Chemical Energetics |
INTEXT QUESTIONS 10.1
1. The enthalpy change for the transition of ice to liquid water at 273 K is 6.02 kJ mol⁻¹. Calculate the entropy change for the process.
Ans: Δ(fus)S = [Δ(fus)H/](T)
= (6.02 × 10³ kJ mol⁻¹)/(273 K)
= 22.0 J mol⁻¹ K⁻¹.
2. Arrange the following systems in the order of increasing randomness,
(i) 1 mol of gas A.
(ii) 1 mol of solid A.
(iii) 1 mol of liquid A.
Ans: 1 mol of solid, 1 mol of liquid, 1 mol of gas.
3. Indicate whether you would expect the entropy of the system to increase or
Decrease:
(a) 2SO₂ (g) + O₂ (g) → 2SO₃ (g)
Ans: Decrease.
(b) N₂ (g) + 3H₂ (g) → 2NH₃ (g)
Ans: Decrease.
(c) O₂ (g) → 2O (g)
Ans: Increase.
INTEXT QUESTIONS 10.2
1. Determine whether the following reaction:
CCl₄ (l) + H₂ (g) → HCl (g) +CHCl₃ (l)
is spontaneous at 298 K if ΔrH = 91.35 kJ mol⁻¹ and ΔrS = 41.5 JK⁻¹ mol⁻¹ for this reaction.
Ans: ΔG = –103.7 kJ. Therefore the reaction is spontaneous.
2. Which of the following conditions would predict a process that is always spontaneous?
(i) ΔH > 0, Δ S > 0
(ii) Δ H > 0, Δ S < 0
(iii) Δ H < 0, Δ S > 0
(iv) Δ H < 0, Δ S < 0
Ans: (iii) ∆H < 0, ∆S > 0
INTEXT QUESTIONS 10.3
1. What is the relationship between the standard Gibbs energy change and the equilibrium constant of the reaction?
Ans: ΔGº = –2.303 RT log K
2. The standard Gibbs energy change for the reaction:
CO (g) + 2H₂ (g) ⎯⎯→ CH₃OH (l)
at 298 K is – 24.8 kJ mol⁻¹. What is the value of the equilibrium constant at 298 k?
Ans: 2.2 × 10⁴
TERMINAL EXERCISE
1. What do you call the measure of disorder or randomness in a system?
Ans: The measure of disorder or randomness in a system is called entropy. It reflects the degree to which energy is distributed randomly within a system, or the level of uncertainty in a system’s state.
2. Predict the sign of Δ S for each of the following processes.
(i) H₂ (g) → 2H (g)
(ii) O₂ (g, 300 K) → O₂ (g, 500 K)
Ans: Predicting the Sign of ΔS
(i) H₂(g) → 2H(g)
In this process, one molecule of H₂ breaks into two atoms of H. This increases the number of particles and the disorder in the system. Therefore, the entropy increases, and ΔS is positive.
(ii) O₂(g, 300 K) → O₂(g, 500 K)
In this process, the temperature of O₂ gas increases from 300 K to 500 K. As temperature increases, the kinetic energy of the molecules increases, leading to more random motion and greater disorder. Therefore, the entropy increases, and ΔS is positive.
3. Define entropy.
Ans: Entropy is a fundamental concept in physics, particularly in thermodynamics and information theory, that quantifies the degree of randomness or disorder within a system. It essentially measures how energy is distributed and how much energy is unavailable to do work. A higher entropy indicates a more disordered state, where energy is spread out and less concentrated for useful work.
4. Explain why entropy is not a good criteria for determining the spontaneity of a process?
Ans: Entropy (ΔS) is a measure of disorder or randomness in a system. While an increase in entropy often favors spontaneity, entropy alone cannot determine whether a process will occur spontaneously.
Reasons:
(i) Entropy of the System Is Not the Whole Picture:
Spontaneity depends on the total entropy change of the universe, which includes:
∆S(universe) = ∆ S(system) + ∆S(surroundings)
(ii) Temperature Affects the Role of Entropy:
The effect of entropy depends on temperature.
For example:
A process with a small positive ΔS might not be spontaneous at low temperatures.
Conversely, a process with negative ΔS can still be spontaneous at high temperatures if the enthalpy change (ΔH) is favorable.
(iii) Enthalpy (ΔH) Also Plays a Role:
Spontaneity depends on both enthalpy (ΔH) and entropy (ΔS).
A highly exothermic reaction (large negative ΔH) can drive a process even if entropy decreases.
Correct Criterion for Spontaneity: Gibbs Free Energy (ΔG)
At constant temperature and pressure:
∆G = ∆H – T∆ S
If ΔG < 0, the process is spontaneous.
This equation balances both energy (ΔH) and disorder (ΔS), making it the correct criterion.
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