PHY 262: First Law of Thermodynamics

Consider a certain object A. Which of the following is an example of its internal energy?

Chemical energy of the object due to possible reactions between different parts of object A

Assume the first law of thermodynamics is given as delta U is equal to Q minus W. Suppose a gas is COMPRESSED in some unknown process. Which of the following is not a possible result?

Decreased T and Q>0

Consider a certain object A. Which of the following is an example of its internal energy?

Elastic energy due to stretched bonds between different parts of object A

Assume the first law of thermodynamics is given as delta U is equal to Q minus W. In this relationship, what does a positive value of Q represent?

Heat, meaning energy being transferred to the system by its environment

Assume the first law of thermodynamics is given as delta U is equal to Q minus W. Suppose a gas EXPANDS in some unknown process. Which of the following is not a possible result?

Increased T and Q<0

When describing a thermodynamic system, which of the following is a good description of "internal energy"?

Internal energy is the energy the system would have even if it were stationary and alone in the universe.

What do the terms "isobaric" and "isochoric" mean in the context of the thermodynamics of a gas?

Isobaric means constant pressure, while isochoric means constant volume.

In thermodynamics, what does it mean for a system to be "closed"?

It means no matter enters or leaves the system.

Consider a certain object A. Which of the following is an example of its internal energy?

Microscopic kinetic energy of the atoms and molecules inside object A

Gravitational potential energy (Ug) is one example of a potential energy. Is the internal energy of a system (often symbolized as U) an example of a potential energy?

No, internal energy does not relate to a conservative force and is not a potential energy.

Consider your own body as the thermodynamic system for this question and assume the first law of thermodynamics is given as delta U is equal to Q minus W. Imagine lifting a very heavy weight very slowly from the floor until it is overhead. Over the duration of this process, what would be the signs of Q and W for your body?

Q<0, W>0

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the pressure and temperature changed in this process? (the line between the two points has an undefined slope, final point on top)

The pressure increased and the temperature increased.

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the temperature of the system changed in this process? (line between two points has an undefined slope)

The pressure increased and the temperature increased.

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the pressure and volume changed in this process? (line between the two points has a negative slope)

The pressure increased and the volume decreased.

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the volume and temperature changed in this process? (line between two points has an undefined slope, initial point on top)

The volume remained the same and the temperature decreased.

Consider the relationship delta U is equal to Q minus W. In this relationship, what does a positive value of W represent?

Work being done by the system on its surroundings

An isothermal process and an adiabatic process ______.

both involve pressure and volume changing inversely (one gets larger while the other gets smaller)

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the temperature of the system changed in this process? (line between two points has a positive slope)

cannot be part of an isothermal, isobaric, or isochoric process

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. The points shown ______. (line between the two points has a positive slope)

cannot be part of an isothermal, isobaric, or isochoric process

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. The points shown ______. (line between two points has a negative slope)

could be part of an isothermal process, could be part of an adiabatic process

Assume the first law of thermodynamics is given as delta U is equal to Q minus W. A system is taken from state 1 to state 2 (each with corresponding pressure, temperature, and volume) in a variety of ways. Which of the quantities in the first law of thermodynamics will be the same in all of the various processes?

delta U

Consider the pV diagram below for a gas made up of a certain number of moles. Each point on the pV diagram has a well-defined ______.

pressure, volume, and temperature

Consider the relationship delta U is equal to Q minus W. In this relationship, what is delta U?

the change in the system's internal energy

Assume the first law of thermodynamics is given as delta U is equal to Q minus W. In a certain process, a gas expands to 120% of its previous volume while its pressure stays constant. What can we say about W for the gas in this process?

W>0

A pV diagram is shown representing the state of a gas in a closed system. Two points are marked, indicating the initial and final states of some process. From these two points, what can we say about how the temperature of the system changed in this process? (line between two points has negative slope)

We cannot tell whether the temperature increased, decreased, or stayed the same.