Thermo Exam Definitions

Question 1

In 35 words or less, define or explain Enthalpy

Answer 1

Enthalpy is a combination property, H = U + pV.

U is microscopic internal energy.

The pV term has the sense of work and relates to flow work.

Question 2

In 35 words or less, define or explain Closed System

Answer 2

A system in which there is a control mass.

Mass cannot cross the system boundary, but energy in the form of heat or work can cross the boundary.

Question 3

In 35 words or less, define or explain Open System

Answer 3

A system in which there is a control volume.

Both mass and energy can cross the system boundary.

Question 4

In 35 words or less, define or explain Property of State.

Answer 4

This is a characteristic of the system that depends only on, and determines, the current equilibrium state of the system.

Question 5

In 35 words or less, define or explain Reversible Process.

Answer 5

The system can be transformed from state 1 to state 2 and back with no trace left on the surroundings.

Question 6

In 35 words or less, define or explain Isentropic Process.

Answer 6

A process in which there is no change in entropy. It is a reversible, adiabatic process.

An isentropic process is adiabatic and frictionless.

Question 7

In 35 words or less, define or explain Thermodynamic Temperature Scale.

Answer 7

A temperature scale that is not dependent on a thermometric material.

It has an absolute zero.

It is defined by thermodynamics.

Question 8

In 35 words or less, define or explain Cyclic Process.

Answer 8

The end state is identical to the start state.

Question 9

In 35 words or less, define or explain Stationary System.

Answer 9

This is a system that exhibits minimal change in kinetic energy or potential energy during a process.

Question 10

In 35 words or less, define or explain The First Law of Thermodynamics

Answer 10

During a cyclic process, the net heat addition to a system is proportional to the net work produced, and vice versa.

Question 11

In 35 words or less, define or explain Internal Energy

Answer 11

Comprised of all microscopic forms of energy in a process.

A property of state following from the first corollary of the first law.

Question 12

In 35 words or less, define or explain Entropy

Answer 12

A Property of State and indication of disorder.

It is defined by dS = dQ_rev/T, and follows as a corollary of the Second Law of Thermodynamics.

Question 13

In 35 words or less, define or explain System Boundary.

Answer 13

The real or imaginary surface separating the system from its surroundings.

Defined so as to identify the flow of mass, heat and work of interest in system analysis.

Question 14

In 35 words or less, define or explain System.

Answer 14

A collection of entities that interest us. Can be a fluid sample of a machine.

Defined by system boundary.

Question 15

In 35 words or less, define or explain Carnot Efficiency.

Answer 15

The Highest Efficiency a heat engine can have when operating between two thermal energy reservoirs at temperatures T_L and T_H ; n = 1 - T_L / T_H

Question 16

In 35 words or less, define or explain Equilibrium

Answer 16

Implies a state of balance.

No net force or heat flow acts on the system.

A system in equilibrium experiences no changes when it is isolated from its surroundings.

Question 17

In 35 words or less, define or explain the Clausius Statement of the 2nd Law of Thermodynamics

Answer 17

It is impossible to construct a machine which in itself will cause heat to pass from a cold reservoir to a hot reservoir with no other effect.

Question 18

In 35 words or less, define or explain Polytropic Process

Answer 18

A process in which pressure and volume are often related by pVⁿ = C, where C and n are constant, during expansion and compression processes of real gases.

Question 19

In 35 words or less, define or explain Isobaric

Answer 19

Indicates constant pressure.

An isobaric process is a process in which the pressure remains constant.

Question 20

In 35 words or less, define or explain Intensive Property

Answer 20

Intensive Properties are those that are independent of the size of a system and are obtained by dividing by the mass of the fluid.

Intensive properties are not additive.

Question 21

In 35 words or less, define or explain Process

Answer 21

Any change that a system undergoes from one equilibrium state to another.

Question 22

In 35 words or less, define or explain Thermodynamics

Answer 22

The science of the relationship between heat and mechanical work.

Also known as the science of energy.

Question 23

In 35 words or less, define or explain Thermal Equilibrium.

Answer 23

A state of balance, in which the temperature is the same throughout the system.

Question 24

In 35 words or less, define or explain Specific Heat Capacity at Constant Volume (c_v)

Answer 24

A measure of the energy required to raise the temperature of a unit mass of substance by one degree as the volume is maintained constant.

Question 25

In 35 words or less, define or explain **Carnot Cycle**

Answer 25

A **cycle** composed of **four reversible processes**, **two isothermal**, **two adiabatic**.

Question 26

In 35 words or less, define or explain **Irreversible Process**

Answer 26

A process that cannot be reversed without leaving a trace on the surroundings.

Question 27

In 35 words or less, define or explain **Kelvin's Statement of the 2nd Law of Thermodynamics**

Answer 27

It is **impossible** for any **device** that **operates on a cycle** to **recieve heat** from a **single reservoir** and **produce** a **net** amount of **work**.

Question 28

In 35 words or less, define or explain **Turbofan Engine**

Answer 28

A large fan driven by the turbine forces air through a cowl surrounding the engine. The fan exhaust leaves at a higher velocity, enhancing the total thrust of the engine.

Question 29

In 35 words or less, define or explain **Pressure**

Answer 29

The force exerted per unit area

Question 30

In 35 words or less, define or explain **Density**

Answer 30

The amount of matter/substance per unit volume

Question 31

In 35 words or less, define or explain **Specific Volume**

Answer 31

The volume of space taken up by one unit of mass.

Question 32

In 35 words or less, define or explain **Adiabatic Process**

Answer 32

A process during which there is **no heat transfer**.

Question 33

In 35 words or less, define or explain **Boundary Work**

Answer 33

(**pdV**) Work associated with expansion or compression of gas in a piston-cylinder.

Question 34

In 35 words or less, define or explain **Isochoric**

Answer 34

(a.k.a. isometric) A process during which the specific volume (-v-) remains constant.

Question 35

In 35 words or less, define or explain **Isolated System**

Answer 35

A closed system in which energy is not allowed to cross the boundary.

Question 36

In 35 words or less, define or explain **Coefficient of Performance (COP)**

Answer 36

The **measure of performance** of **refrigerators** and **heat pumps**.

Question 37

In 35 words or less, define **isentropic efficiency.**

Answer 37

**Isentropic efficiency** is the ratio of **real world work** to **reversible work**. n = W/W' = (h₂ - h₁) / (h₂' - h₁)