Thermodynamic

Question 1

What is the first law of Thermodynamic?

Answer 1

The energy cannot be created or destoryed. The change in internal energy is delta U= q+w.

Question 2

Define Enthalpy.

Answer 2

Enthalpy is the sum of internal energy and the product of pressure and volume H=U+PV. At constant pressure, the change in enthalpy is Delta H=q(p).

Question 2

What is a state function? give examples

Answer 2

The state function only depends on the current state of the function, not the path taken. eg: Internal energy, Enthalpy, Temperature and Pressure.

Question 3

what is the difference between the exothermic and endothermic reaction?

Answer 3

exothermic releases heat. delta H >0
endothermic absorbs heat. delta H<0

Question 4

what is the equation of work done by a gas expansion or compression?

Answer 4

w= -P(ext)delta V at constant external pressure

Question 5

Why is the internal energy a state function but not work and heat?

Answer 5

Internal energy depends only on the state of the system (initial and final states) not the process, while heat and work depends on the path taken during the energy transfer, making them path functions.

Question 5

Explain why the first law of thermodynamic is the statement of energy conservation?

Answer 5

The first law states that the total energy on an isolated system is conserved. delta E= q+w. Energy added as heat or work changes. The internal energy does not create or destroy energy.

Question 6

why can energy transfer only occur as heat or work in thermodynamic?

Answer 6

Energy transfer must involve the interaction between the system and the surroundings. Heat occurs due to the temperature changes and work occurs when forces cause displacement or volume change.

Question 7

Why is enthalpy an extensive property, and what does this mean for thermodynamic calculations?

Answer 7

The enthalpy depends on the amount of the substance present. for example doubling the amount of moles in reaction doubles delta H, making the enthalpy calculation scales with system size.

Question 8

Why does the work done during gas expansion depend on whether the process is reversible or irreversible?

Answer 8

In reversible process, the external pressure is continuously changing to match the internal pressure, maximizing work, while in irreversible process, the external pressure is constant resulting in less work.

Question 8

How does calorimetry demonstrate the First Law of Thermodynamics?

Answer 8

In calorimetry, the energy gained by the system is equal to the energy lost by the surroundings and vice vasa. The first law reflects the energy is conserved.

Question 9

In terms of thermodynamics, why are equilibrium states time-independent?

Answer 9

At equilibrium, macroscopic properties (e g. pressure, volume, temperature) remain constant over time because the system has no net energy flow.

Question 10

How does the Zeroth Law of Thermodynamics explain the working principle of a thermometer?

Answer 10

the thermometer comes into the equilibrium with a system. By the zero law, both the system and the thermometer share the same temperature, allowing the temperature measurement.

Question 11

Is enthalpy and heat equal?

Answer 11

No, enthalpy and heat are not the same thing. However, under specific condition, the change in enthalpy (delta H) is approximately equal to the heat (q) transferred.

Question 12

Explain why enthalpy and heat are not the same.

Answer 12

1.Enthalpy is a state function while heat is not.2. Enthalpy include pressure and volume work while heat account for energy transferred due to temperature difference.3. Heat and enthalpy are equal under specific conditions.(under constant pressure) Enthalpy is the thermodynamic property which depends only on the current state of the system. Heat on the other hand depends of the specific pathway used from one state to another.

Question 13

Explain the First Law of Thermodynamics using the equation
dU=đq+đw. What is the difference between exact and inexact differentials in this context?

Answer 13

Exact Differential or
The internal energy (delta U) is a state function, meaning its value depends only on the initial and final states of the system, not on the path taken. while inexact differential heat (q) and work (w) are path functions, so their values depend on the specific process taken to transfer energy.

Question 14

What does heat capacity of a substance depends on?

Answer 14

depends on how it’s molecule can store energy. Substances with more ways to store energy ( more degrees of freedom) will have higher heat capacity.

Question 15

Why does water has larger heat capacity?

Answer 15

When heat is added to the water, a significant energy is used to break hydrogen bonds, rather than increasing the KE(T) of the molecules, which makes water molecules to store energy in multiple ways. The ability to absorb energy in various forms contributes its high heat capacity.

Question 16

How does heat capacity depend on degree of freedom?

Answer 16

The more degree of freedom ( translational, vibrational, rotational) the higher the heat capacity. Energy is stored and distributed among these forms.

Question 17

what is internal energy? why is it difficult to measure directly?

Answer 17

Internal energy depends on the kinetic and potential energy of a system. It cannot be measured directly because it includes macroscopic contributes. only changes in internal energy can be measured.

Question 18

define heat capacity and specific heat.

Answer 18

Heat capacity: energy required to raise the temperature of an object by 1 K.
Specific heat: Energy required to raise 1 gram of a substance by 1 K.
q=m s deltaT

Question 19

What is the difference between constant pressure calorimetry and constant volume calorimetry?

Answer 19

Constant pressure calorimetry :measures the heat exchanged (delta H) at constant pressure allowing work to be done.( e g. reaction in solutions where pressure changes are negligible
Constant volume calorimetry: measures the internal energy (delta U) at constant volume ,preventing work from being done. (its ideal for reaction like combustion where significant pressure changes occur.

Question 19

Why do gases typically have lower heat capacities than liquids or solids?

Answer 19

Gases primarily store energy through translation motion. In liquid and solid, energy also store through rotational and vibrational motions, leading to larger heat capacity.

Question 20

how Hess’s Law simplifies enthalpy calculations for complex reactions

Answer 20

Hess’s law allow to break down complex reaction into simple steps. Since Enthalpy change is a state function, the total delta H of reaction equals to sum of delta H of each steps.

Question 21

What is the significance of Hess’s Law in thermodynamics, and how can it be applied to determine the enthalpy change of a reaction?

Answer 21

Hess’s law states that the total enthalpy change of a reaction only depends on the initial and final steps of the system not on the path taken. This allows enthalpy change of a complex reaction can be determined by summing the enthalpy changes of simpler known steps.