Two ways energy crosses a boundary; neither is a property of the system.
Heat Q is energy transferred due to temperature difference; work W is energy transferred by other means (boundary movement, shaft, electrical). Both are path functions, not properties. Sign convention: heat in positive, work out positive (engineering).
Gas expanding against a piston does boundary work.
Heat and work are the two ways energy crosses a boundary, so distinguishing them is essential for correct energy balances.
Two ways energy crosses a boundary; neither is a property of the system.
Heat and work are the two ways energy crosses a boundary, so distinguishing them is essential for correct energy balances.
They describe energy in transit across a boundary, while properties describe the state of a system, so they depend on the path.
A common convention counts heat added to the system and work done by the system as positive, but any clear convention works if it is applied consistently.
Typical applications include deciding whether a compressor input is work or heat in a cycle, accounting for heat loss through an insulated wall and recognising that stirring a liquid adds work rather than heat.
Study "Specific heat" first (topic 7 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Boundary work W=∫P dV. Shaft work. Adiabatic means Q=0.
Gas expanding against a piston does boundary work.
The next topic is "Internal energy and enthalpy", which builds directly on this one.
It is classed as Beginner in Thermodynamics & Fluids (topic 8 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
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