Intermediate Topic 335 of 1102 Thermodynamics & Energetics
Work in Chemistry
Energy transferred by force over distance; pressure-volume work equals -P times change in V.
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In-depth explanation of Work in Chemistry
Work is energy transferred when a force moves an object through a distance. In chemistry the most important form is pressure-volume work, which arises when a gas expands or is compressed against an external pressure. It is calculated as w equals minus P_ext times the change in volume, so an expansion, where volume increases, gives a negative w, meaning the system does work on the surroundings and its internal energy falls. Compression gives a positive w, meaning work is done on the system. Electrical work is equally important in electrochemistry, where the maximum electrical work from a cell is linked to the Gibbs energy change of the reaction.
Going deeper: Work in Chemistry
Key ideas: Pressure-volume work is w equals minus P_ext delta V. Use the external pressure, not the gas pressure, for an irreversible process. Reaction gas production does work against the atmosphere, and for ideal gases at constant pressure it equals minus delta n R T, where delta n is the change in moles of gas. Units: pressure times volume in litre atmospheres converts at 101.325 joules per litre atmosphere.
Common mistakes and connections: The commonest error is the sign: expansion gives negative w. Another is forgetting the unit conversion between litre atmospheres and joules. Do not apply the formula to a free expansion into vacuum, where P_ext is zero and w is zero. This topic leads directly to the difference between delta U and delta H.
Visualization of Work in Chemistry
Pressure-volume work equals the area under a P-V curve. Expansion along an isotherm shows how much work a gas does as its volume increases. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A gas produced inside a cylinder that pushes a piston outward performs expansion work on the surroundings.
Frequently asked questions about Work in Chemistry
What is Work in Chemistry?
Energy transferred by force over distance; pressure-volume work equals -P times change in V.
Is Work in Chemistry a beginner, intermediate or advanced topic?
Work in Chemistry is a intermediate topic in Thermodynamics & Energetics. It builds on the vocabulary of beginner topics in this area.
What should I learn before Work in Chemistry?
Study these earlier topics in Thermodynamics & Energetics first: Path Function, Energy, Heat.
What comes after Work in Chemistry?
The next topics in Thermodynamics & Energetics are Internal Energy and First Law of Thermodynamics.
Can I practise Work in Chemistry with quizzes?
Yes. The interactive lesson includes a self-check question on Work in Chemistry, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Work in Chemistry fits in Thermodynamics & Energetics
Work in Chemistry is topic 7 of 91 in Thermodynamics & Energetics.