Thermodynamics 6

Question 1

The decrease in entropy is the only criterion for spontaneity. Do you agree? Why?

Answer 1

According to the second law of thermodynamics, the total entropy of an isolated system always increases over time or remains constant in ideal cases. However, this does not mean that every process with a decrease in entropy is spontaneous. The spontaneity of a process depends on the balance between enthalpy and entropy changes.

Question 2

Exothermic reactions are accompanied by the decrease in entropy are spontaneous at lower temperatures.
Justify on the basis of Gibb’s equation.

Answer 2

Exothermic reactions release heat (ΔH < 0) and often result in a decrease in entropy (ΔS < 0). According to Gibbs’ equation (ΔG = ΔH - TΔS), at lower temperatures (T), if ΔH and ΔS are both negative, ΔG becomes more negative, making the reaction spontaneous.

Question 3

How is delta G helpful in finding the spontaneity of a reaction?

Answer 3

When ΔG is negative (ΔG < 0), it indicates a spontaneous process. If ΔG is positive (ΔG > 0), the process is non-spontaneous. A ΔG of zero (ΔG = 0) signifies equilibrium.

Question 4

Define Internal energy

Answer 4

• It is the energy withing the system is the sum of different types of energies like chemical, electrical, mechanical, etc…
• It is a state function.

Question 5

Thermochemical equation

Answer 5

It is a chemical equation which includes the heat change occurring during a chemical reaction.

Question 6

What is the driving force of a spontaneously occurring changes?

Answer 6

• Increase in entropy
• Decrease in enthalpy.

Question 7

Is decrease in enthalpy the only criteria for stability?

Answer 7

No, to acquire maximum stability, the system tends to have minimum energy.

Question 8

How does heat influence the system?

Answer 8

Whenever heat is added to a system, it increases molecular motions causing increase in the randomness of the system. So heat has an influence on system.
- The system at higher temperature has a greater randomness heat than the system at lower temperature.
- Heat added to a system at lower temperature causes greater randomness than the same quantity of heat is added to it in higher temperatures.

Question 9

define driving force of the process.

Answer 9

The tendency of minimum energy and maximum randomness the resultant of these two which gives the overall tendency for a process to occur is called the driving force of the process.

Question 10

Define Gibbs energy

Answer 10

Gibbs energy is the thermodynamic quantity of a system the decrease in whose value during a process is equal to maximum possible useful work that can be obtained from the system.

Question 11

Why a real crystal has more entropy than an ideal crystal?

Answer 11

A real crystal has some disorder due to the presence of defects in it while ideal crystal has no disorder.

Question 12

Under what conditions delta H becomes equal to delta U?

Answer 12

• When the no. of moles of gaseous products is equal to the no. of moles of gaseous reactants.
• When the reaction does not involve any gaseous products and reactants

Question 13

What is the main limitation of the 1st law of Thermodynamics?

Answer 13

It cannot predict the spontaneity of a system.

Question 14

What is free energy?

Answer 14

It is the capacity to do useful work

Question 15

State the 2nd Law of Thermodynamics.

Answer 15

Naturally occurring processes are accompanied by increase in entropy so the entropy of the universe is continuously increasing.

Question 16

Define 3rd Law of Thermodynamics.

Answer 16

The entropy of all perfectly crystalline solids may be taken as zero at the absolute zero of temperature zero Kelvin.

Question 17

Application of 3rd law of thermodynamics.

Answer 17

It helps in the calculation of absolute entropy of substances at room temperature.

Question 18

Entropy of diamond is less than that of Graphite Why?

Answer 18

in diamond, all the carbon atoms are linked to form and network structure while graphite has two layered structure and can easily slide over one another. Since entropy depends on disorderness, diamond will have less entropy.

Question 19

State the thermodynamic conditions of spontaneous occurrence of a process.

Answer 19

• delta H should be negative and Delta S should be positive for a process to be spontaneous at any temperature.
• When both Delta H and Delta S are positive then the temperature should be high.
• When both Delta H and Delta S are negative then the temperature should be low.

Question 20

what is meant by entropy driven reaction? How the reaction with the positive charge of entropy and enthalpy made entropy driven?

Answer 20

For a reaction to be spontaneous, Delta H should be negative if both Delta H and delta S are positive delta G will be negative that is, T delta S > delta H, The entropy factor dominates the enthalpy factor such reactions are known as entropy driven reactions first up when Delta H and Delta S are positive, Delta G can be negative by raising the temperature.