# Thermodynamics and Entropy Concept

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## 31 Questions

### What is the equation for work during reversible expansion of an ideal gas?

Vf w rev = - ∫ pin dV

Zero (w = 0)

### For an isothermal irreversible change of an ideal gas, what is the relationship between heat and work?

q = -w = pex (Vf - Vi)

p = nRT/V

### What is the work done during adiabatic change of an ideal gas?

w = -nRT ln(Vf/Vi)

### In the given scenario, how much heat is absorbed and how much work is done during the isothermal expansion of the gas?

Heat absorbed: 0, Work done: 0

Negative

### What does a negative value of qp indicate in a reaction?

Exothermic nature

q = CV × ∆T

### What does a positive value of qp indicate in a reaction?

Endothermic nature

### What is the enthalpy change for the combustion of 1 mol of graphite?

-2.48 × 10^2 kJ mol^–1

∆ H = ∆ U

### What is the reason why reactions are often carried out at high temperature?

The positive entropy change of the system can be 'small', in which case T must be large.

### What is the natural direction of a spontaneous change in an isolated system?

Increase in entropy

### How does the second law of thermodynamics explain the common occurrence of spontaneous exothermic reactions?

By stating that heat released by the reaction increases the disorder of the surroundings, leading to a positive overall entropy change.

### What are the three types of molecular motions that contribute to entropy increase with rising temperature?

Translational, rotational, and vibrational motion

### What happens to entropy when the temperature of a system rises?

Entropy increases

### What happens to entropy when the temperature of a system is lowered?

Entropy decreases

### What is entropy in the context of thermodynamics?

Entropy is a measure of the degree of randomness or disorder in a system.

### How does entropy change in relation to the disorder in an isolated system?

The higher the disorder in an isolated system, the higher the entropy.

### What does an increase in entropy in a chemical reaction signify?

An increase in entropy in a chemical reaction indicates a higher disorder in the products compared to the reactants.

### How can entropy change be estimated qualitatively in a chemical reaction?

Entropy change in a chemical reaction can be estimated by considering the structures of the species involved.

### What state of a substance has the lowest entropy?

The crystalline solid state has the lowest entropy.

### Which state of a substance has the highest entropy?

The gaseous state has the highest entropy.

-92.4 kJ mol–1

-238.5 kJ mol–1

### Calculate the enthalpy change for the process CCl4(g) → C(g) + 4 Cl(g) and the bond enthalpy of C – Cl in CCl4(g).

∆H = 485.0 kJ mol–1, Bond enthalpy of C – Cl = 121.25 kJ mol–1

0

T > 2000 K

∆H = 0, ∆S > 0

### Calculate ∆G for the reaction 2 A(g) + B(g) → 2D(g) and predict its spontaneity.

-10.5 kJ, Non-spontaneous

Test your knowledge on thermodynamics and entropy, including the tendency of energy to become more disordered in an isolated system, and how entropy is a measure of this disorder. Explore the relationship between spontaneous change and the concept of entropy.

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