What makes a process quasi-static?

It proceeds through states that remain close to thermal equilibrium, allowing pressure to be specified along the path.

What is the work done by an ideal gas during an isothermal change?

For $n$ moles, $W=nRT\ln(V_2/V_1)$, where $T$ is constant.

What does the van der Waals parameter $a$ represent?

It accounts for intermolecular attractions in the van der Waals equation of state.

What is the internal energy of a monatomic ideal gas?

For $n$ moles, $E_{\text{int}}=\frac{3}{2}nRT$; it depends only on temperature.

How does heat differ from internal energy?

Heat is energy transferred because of a temperature difference; internal energy is energy of the system's particles.

ThermodynamicsLesson 2 of 3 in the course The First Law of Thermodynamics

Pressure–Volume Work, Internal Energy, and the First Law

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

In mechanics, work occurs when a force moves an object through a displacement. In thermodynamics, a gas can do work by expanding against a movable piston, or work can be done on the gas by compressing it. This lesson develops the pressure–volume description of that work.

Consider gas in a cylinder with a movable piston of face area $A$ . If the gas pressure at the piston is $p$ , the gas exerts a force of magnitude $F=pA$ . When the piston moves outward a small distance $dx$ , the gas volume increases by $dV=A\,dx$ . The small amount of work done by the gas is therefore

All flashcards

What makes a process quasi-static?: It proceeds through states that remain close to thermal equilibrium, allowing pressure to be specified along the path.
What is the work done by an ideal gas during an isothermal change?: For $n$ moles, $W=nRT\ln(V_2/V_1)$ , where $T$ is constant.
What does the van der Waals parameter $a$ represent?: It accounts for intermolecular attractions in the van der Waals equation of state.
What is the internal energy of a monatomic ideal gas?: For $n$ moles, $E_{\text{int}}=\frac{3}{2}nRT$ ; it depends only on temperature.
How does heat differ from internal energy?: Heat is energy transferred because of a temperature difference; internal energy is energy of the system's particles.

Quiz questions

An ideal gas with $n$ moles expands isothermally from $V_1$ to $V_2$ . Which expression gives the work done by the gas?Answer: $nRT\ln(V_2/V_1)$
A gas expands from $V_1$ to $V_2$ at constant pressure $p$ . What is the work done by the gas?Answer: $p(V_2-V_1)$
For one mole of a van der Waals gas, which expression gives pressure as a function of volume and temperature?Answer: $p=RT/(V-b)-a/V^2$
A monatomic ideal gas contains $n$ moles at absolute temperature $T$ . What is its internal energy?Answer: $\frac{3}{2}nRT$
A system receives $500\,\text{J}$ of heat and does $200\,\text{J}$ of work. Using $\Delta E_{\text{int}}=Q-W$ , what is its internal-energy change?Answer: $300\,\text{J}$

Based on University Physics Volume 2 by Samuel J. Ling, William Moebs, Jeff Sanny (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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