Thermo CH 2

What can the definition of work in the mechanical sense measure in terms of thermodynamics?

-To evaluate the work done in the compression or expansion of gas or liquid. -The extension of a solid bar (?) -The stretching of a liquid film

Considering the energy balance equation ΔE = Q - W, why is the algebraic sign for heat positive and the algebraic sign for work negative?

A minus sign appears before W because energy transfer by work from the system to the surroundings is taken to be positive. A plus sign appears before Q because it is regarded to be positive when the heat transfer of energy is into the system from the surroundings.

What process occurs if a system undergoes a process involving no heat transfer with its surroundings?

Adiabatic means "without heat transfer," and therefore when a system undergoes a process in which a transfer of heat from the system to the surroundings does not occur the system has undergone an adiabatic process.

Why must the phrase net amount be carefully applied concerning energy transfers?

Because energy transfers that occur through transfers of heat energy or due to work may occur at many different places of the boundary of the system, and the direction of transfer (into the system from the surroundings or into the surroundings from the system) might vary at different places on the boundary of the system. Therefore, the net amount of energy transferred into a system and net energy transferred out of a system must consider the result of all energy transfers by heat and work taking place during the time interval under consideration.

When gas is contained within a piston/cylinder assembly, what is a result and how is it expressed?

Contained gas exerts a normal force on the piston force where F(gas on piston)= p(gas)*A(piston)

In the absence of friction, which macroscopic contributions to the total energy of a system change according to an inverse relationship?

Energy is converted between kinetic energy and potential energy. An increase in kinetic energy results in a decrease in potential energy, and vise versa.

What is a result of work being done by a system and work being done on a system, respectively?

Energy is transferred from a system which has done work, and energy is stored by a system to which work has been done.

What is a polytropic process

For any quasi-equilibrium process that follows a form PVto^n=C. Where n is related to the process.

How does one microscopically quantify the time rate of energy transfer by conduction in a solid, a liquid, or a gas?

Fourier's Law of Heat Conduction states that the rate of heat transfer is directly proportional to the area normal to the direction of heat-flow and directly proportional to temperature gradient. Recall the dot above the symbol for heat energy, Q, which indicates a net heat transfer rate.

Why is kinetic energy considered to be a property of a system?

From the definition of kinetic energy, we observe that it is the product of two extensive, mass/time/length-dependent properties (mass and velocity), from which an intensive property results. Kinetic energy only depends on mass and velocity, and can be measured independent of the history of the system.

Describe the PVT graph provided. What axis and value are constant is process 1-2 (an again with 2-3) and what value is changing on an unfixed axis? Is the changing value increasing or decreasing? From this what kind of process can we conclude occurred in 1-2 and then in 2-3? What is the overall process that occurred from 1-2-3

In process 1-2 the y-axis value of pressure is constant while the process goes forward in the positive-x direction showing volume expansion. Therefore this is a constant pressure and volume-expansion process. In process 2-, the y-axis value of pressure increases in the positive y-direction. Simultaneously the x-axis value of volume remained constant. Therefore process 2-3 is a constant volume process with increasing pressure. To summarize, process 1-2-3 is a constant pressure-expansion followed by a constant-volume increasing pressure process.

What three forms of energy compose the total energy of a system?

Kinetic energy, K Gravitational potential energy, PE Internal energy, U

What category of property are the three macroscopic contributions to the total energy of a system?

Kinetic energy, gravitational energy, and internal energy are all extensive properties of a system.

What is another term describing work resulting from expansion and compression?

Moving boundary work

In what way can a close system interact with their surroundings in a way that cannot be categorized as work?**

No work occurs when there is an energy transfer by heat, but when the temperature of a system differs from the temperature of the surroundings there is a transfer of energy that occurs.**

If we know the net rate heat of transfer, in principle, how can the energy transfer by heat be determined during a known time period?

One can integrate the net rate of heat transfer from t1 to t2 to determine the energy transfer by heat.

What symbol denotes an amount an amount of energy transferred across the boundary of a closed system in the form of a heat energy transfer? What symbol denotes the net rate of heat transfer?

Q = Amount of energy transferred between a system and its surroundings.. The symbol for the net rate of heat is the symbol for heat (Q) with a dot above the symbol.

What three macroscopic contributions contribute to the change in total energy of a system?

The change in kinetic energy, the change in gravitational potential energy, and the change in internal energy of the system.

What is the direct symbolic translation (formula) of energy balance and what is the alternative form for this direct translation?

The change in the amount of energy contained within a system during some time interval is equivalent to: (the net amount of energy transferred in across the system boundary by heat transfer, minus the net amount of energy transferred out across the system boundary by work) during the time interval under consideration. ΔE = Q - W --> ΔKE +ΔPE +ΔU = Q - W

What does the value of heat transfer depend on? What does this dependence infer about the nature of heat?

The details of a process and not solely on the amount of heat held by the systems and its surroundings. Because heat depends on processes and the history of the system, it is not a property.

What is the rate of energy transfer done by work equivalent to and what is the corresponding formula?

The rate of energy transfer by work is equivalent to the dot product of the of the force and the velocity at the point of application of the force

Why is important to consider the rate at which energy transfer occurs when work is done by/on a system in thermodynamic analysis? What term do we use to describe this measurable occurrence?

The rate of energy transfer done by work is called power.

In the absence of friction, what macroscopic contributions to the total energy of a system remain constant?

The total energy of a system, E, and the internal energy of a system, U remain constant in the absence of friction.

Why is work not a property of the system?

The value of W depends on the details of the interactions taking place between the system and surroundings during a process and not just the initial and final states of the system. It follows that work is not a property of the system or the surroundings and depends on the processes and history of the systems.

Why is work not an extensive or intensive property of a system or of the surroundings of the system?

The value of work depends on the processes occurring in the interactions and all the details therein, therefore the value of work is not equivalent to Work, final - Work, initial. From this, we can observe that work is not able to be considered a mere property of the systems or of the surroundings and requires knowledge of a systems='s history and processes to evaluate.

What determines the sign convention for work in thermodynamics

W>0: work done by the system is considered to be positive work. Work by System --> Q+ W<0: work done on the system is considered to be negative work. Work on System --> Q-

When is heat transfer between a closed system and its surroundings considered to be positive? When is such a transfer of energy considered to be negative?

When heat is transferred from surroundings into a system, the energy transfer by heat (Q) is positive. Energy into system --> Q+ When heat is transferred from a systems into the surroundings the energy transfer by heat (Q) is negative. Energy out of system --> Q-

When is a differential not able to be considered exact?

When the quantity being measured requires an understanding of processes occurring and not just of measurable properties.

While there is no transfer of mass within a closed system, how can a closed system interact with the system's surroundings?*

When there is a temperature difference between the system and the surroundings of the system an interaction that occurs is: Energy Transfer By Heat.*

When is work considered to be positive in terms of thermodynamics that is in contrast to the approach taken in mechanics? When is work considered to be negative in terms of thermodynamics that is in contrast to the approach taken in mechanics?

Work done by a system is considered to be positive in thermodynamics. Work done on the system is considered to be negative.

What criterion must be satisfied when considering the thermodynamic definition of work? What differentiates this difference from energy in the sense of dynamic and potential energy and what are some examples?

Work is done by a system on its surroundings if the sole effect on everything external to the system could have be equivalent to the raising of a weight (CONFUSING) and considers internal energy that cannot be expressed by kinetic energy or gravitational potential energy. When work done on a system cannot be attributed to kinetic energy or potential energy, it is therefore considered to be the result of the internal energy of a system. Kinds of work that are included in this category of internal energy of a system include: Chemical, rotational, magnetic, and electrical energies are internal energies of a system that are explained by the thermodynamic definition of work. This addition of internal energy to the total energy of a system differentiates the defintion of work in the therm

What word statement is an accounting balance for energy and its corresponding formula?

ΔE = Q - W