Thermodynamics 1

Question 1

State zeroth law: (2)

Answer 1

If object A is in thermal equilibrium which object B
And object B is in thermal equilibrium with object C
Then object A and C are in thermal equilibrium

Question 2

What does thermal equilibrium mean (2)

Answer 2

-When the temprature have balanced out, heat stops flowing
-so the system or set of systems are said to be in thermal equilibrium

Question 3

What are the physical quantities that are equal when being in thermal equilibrium (3)

Answer 3

-temperature
-work done
-head added

Question 4

State the first law of thermodynamics (3)

Answer 4

-it is a statement of energy conservation
-energy cannot be created or destroyed it can only be transferred
U=Q-W

Question 5

What does internal energy mean (1)

Answer 5

It is the sum of potential energy and kinetic energies

Question 6

What happens to the internal energy when, the system does work but no heat is added, mention a formula (2)

Answer 6

Internal energy decreases
U = Uf - Ui = -W

Question 7

State what happens to heat when
A) system gains heat
B) system loses heat (2)

Answer 7

A) Q+
B) Q-

Question 8

State what happens to work done when
A) work done on the system
B) work done by the system (2)

Answer 8

A) W-
B) W+

Question 9

Define quasi static (2)

Answer 9

-They occur so slowly that at any given time the system and it’s surrounding are in equilibrium
-also assuming they are reversible

Question 10

State factors that could determine is a process is quasi static or not and why (4)

Answer 10

Equilibrium at all times:
-pressure and temperature are uniform throughout

Reversibility:
-they can be reversed without any net change in the system or surrounding

Question 11

What conditions must be met for a process to be considered reviserible in thermodynamics (2)

Answer 11

-it must be to return the system and it’s surrounding to the same states they were in before the process began

Question 12

Why are processes not entirely reversible (2)

Answer 12

-because there can be some degree of irreversibility such as
Friction and heat transfer

Question 13

In an idealized reversible process involving gas compression, how is the temperature of the gas maintained? (1)

Answer 13

-in an idealized reversible process involving gas compression the temperature is maintained at a constant value

Question 14

This is an idealized process as described:
The gas is compressed, the temperature is constant, so heat leaves the gas. As the gas expands, it draws heat from the reservoir returning the gas and the reservoir to their initial states. This piston is assumed frictionless

In the context of the idealized reversible process, why is it important for the gas and reservoir to return to their initial states (2)

Answer 14

-It is important to return to their initial states in the idealized reversible process to ensure reversibility
-where no net change occurs in the system or it’s surrounding

Question 15

This is an idealized process as described:
The gas is compressed, the temperature is constant, so heat leaves the gas. As the gas expands, it draws heat from the reservoir returning the gas and the reservoir to their initial states. This piston is assumed frictionless

How does a frictionless piston impact the described idealized process (2)

Answer 15

-a frictionless piston in the idealized reversible process allows mechanical work to be done without any energy loss due to friction
-so that contributes to reversibility

Question 16

The gas is compressed, the temperature is constant, so heat leaves the gas. As the gas expands, it draws heat from the reservoir returning the gas and the reservoir to their initial states. This piston is assumed frictionless

What condition characterizes the idealized reversible process, ensuring that it can return the system and surrounding to their original states (2)

Answer 16

-the process is characterized by its ability to return both the system and it’s surrounding to their original stats, ensuring no net changes in the overall systems properties

Question 17

State the formula for work done by an expanding gas at constant pressure (1)

Answer 17

W = PV

Question 18

What are the characteristics when volume is constant (2)

Answer 18

• Work done is zero
• change in internal energy = heat

Question 19

What are the characteristics of constant pressure processes (2)

Answer 19

W = PV
Q = U + PV

Question 20

What is the relationship between pressure and volume in an isothermal process where the temprature remains constant (4)

Answer 20

-In an isothermal process with constant temprature,
-the pressure and volume are inversely proportional
-this means the volume of the gas increases as the pressure decreases
-provided temperature remains constant

Question 21

In isothermal process, how is the work done calculated (1)

Answer 21

Area under the graph

Question 22

State the formula used to calculate the work done in isothermal process using calculus (1)

Answer 22

W = nRTln (Vf/Vi)

Question 23

What is an Adiabatic process, and how does it differ from an isothermal process (3)

Answer 23

-an adiabatic process is one in which no heat flows into or out of the system
-in isothermal the temprature remains constant
-whereas in adiabatic the temperature of system can change

Question 24

How can insulation be used to ensure that a process is adiabatic? Explain the role of insulation in preventing heat exchange with the surrounding (3)

Answer 24

-insulation is used to ensure that a process is adiabatic by preventing heat exchange with the surrounding
-it creates a barrier that minimizes heat transfer into or out of the system
-allowing the process to maintain adiabatic conditions

Question 25

Compare and contrast the PV curves of adiabatic and isothermal processes. Which graph is more steeper and why (3)

Answer 25

-the adiabatic curve is steeper than the isothermal one because
-the temperature changes during the adiabatic process
-as a result the pressure and volume relationship is more sensitive to volume changes
-leading to a steeper curve

Question 26

Provide an example of a real world situation where insulating a system is crucial to maintain an adiabetic process. Explain why adiabtic conditions are necessary in this context (3)

Answer 26

-thermos bottle
-insulation in a thermos prevents heat transfer into or out of the container
-ensuring that the liquid inside remains at a constant temprature

Question 27

Compare the work done in an adiabatic process with that in isothermal. Discuss the key differences in the formulas and the underlying principles (2)

Answer 27

-the work done in an adiabatic process is given by W= -U
-whereas in isothermal process the work done is W = Q and W = nRTln(Vf/Vi)

Question 28

Explain why the absence of heat exchange (adibaticity) is essential in certain industrial processes, such as compressing air. How does this impact efficiency and performance (2)

Answer 28

-they are crucial because they ensure that the systems temperature does not fluctuate due to heat transfer
-this stability improves efficiency and control over the process preventing temorature related issues

Question 29

Describe the role of energy conservation in adiabatic processes. Why is it crucial to account for the changes in internal energy without heat exchange (2)

Answer 29

-because in the absence of heat exchange, any change in the systems internal energy directly affects the work done or the energy used to perform work
-the energy in the system remains constant

Question 30

In an adiabatic expansion of an ideal gas, does the temperature increase or decrease? Explain the temperature change and its relationship with pressure and volume changes. (4)

Answer 30

-In an adiabatic expansion of an ideal gas, the temperature decreases.
-As the gas expands, it does work on the surroundings,
-which results in a decrease in internal energy and, consequently, a decrease in temperature.
-This is why the adiabatic process is often associated with cooling effects.

Question 31

In an adiabatic process for an ideal gas, how does the pressure (P) relate to the volume (V) when no heat exchange occurs? Express this relationship mathematically. (2)

Answer 31

-the pressure (P) and volume (V) are related by the equation P₁V₁^γ = P₂V₂^γ,
-where γ is the adiabatic index (also known as the heat capacity ratio), which is specific to the gas being considered. 5/3 is the adiabatic index

Question 32

State the characteristics of adiabatic process (2)

Answer 32

W = -U

Q = 0

Question 33

What happens when internal energy increases in an adiabatic process (4)

Answer 33

• there’s no heat transfer Q=0
  -the change in internal energy is equal to the heat added and work done by the system
  U = -W
  -change in internal energy will be positive
  -therefore work done is done on the system as W is negative

Question 34

Define molar specific heat of a substance (2)

Answer 34

-the amount of heat required
-to raise the temperature of 1 mole of the substance by 1 degree Celsius

Question 35

Molar specific heats for ideal gases must be quoted either at… (2)

Answer 35

-constant pressure
-constant volume

Question 36

State the formula for molar specific heats for ideal gases for a constant volume process (3)

Answer 36

Heat = moles x Cv x change in temperature

Cv = heat / moles x change in temperature

Cv = 3/2 R

Cp - Cv = R

Question 37

State the formula for molar specific heats for ideal gases for a constant pressure process (3)

Answer 37

Heat = moles x Cp x change in temperature

Cp = heat / moles x change in temperature

Cp = 5/2 R

Cp - Cv = R

Question 38

State the formula for the PV curve for an adiabat (2)

Answer 38

P(V)^Y = constant

Y = 5/3

Question 39

What is the difference between an open system and a closed system in thermodynamics (2)

Answer 39

-an open system can exchange both matter and energy with its surrounding,
-closed system can only exchange energy but not matter

Question 40

Explain the concept of adiabatic processes in thermodynamics (3)

Answer 40

-an adiabatic process is a thermodynamic process in which there is no heat exchange between the system and surrounding
-this means that Q=0
-and W = -U