--- title: "Heat transfer vs work transfer" subject: "Fundamental of Thermodynamics & Heat Transfer" chapter: 2 key: "semester_2/fundamental_of_thermodynamics_and_heat_transfer:heat-vs-work-transfer-difference" source: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/heat-vs-work-transfer-difference site: BCT Engineering --- # Heat transfer vs work transfer Fundamental of Thermodynamics & Heat Transfer · Chapter 2: Energy and Energy Transfer - Asked in: 2071 Bhadra, 4 marks; 2070 Bhadra, 4 marks (asked 2 times) - Video: [Work & Heat Transfer](https://www.youtube.com/watch?v=1qI7Ys1Of6o) — TutorialsPoint - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/heat-vs-work-transfer-difference - Whole chapter: https://www.bctengineer.com/md/semester_2/fundamental_of_thermodynamics_and_heat_transfer/chapter-2 ## Question Differentiate between heat transfer and work transfer. ## Short answer Heat transfer is boundary energy transfer due solely to temperature difference, disorganized and not fully convertible to work in a cycle. Work transfer is energy transfer from non-thermal potentials (e.g., force, pressure), organized and fully convertible to heat. Both are path functions; heat into system positive, work done by system positive. ## Answer | Basis | Heat transfer | Work transfer | |---|---|---| | Definition | Energy crossing the boundary due to temperature difference | Energy crossing the boundary due to any potential other than temperature (force × displacement, etc.) | | Cause | Temperature difference | Force, pressure, voltage difference | | Nature of energy | Disorganised (random molecular motion) | Organised (ordered motion) | | Modes | Conduction, convection, radiation | Boundary work, shaft work, electrical work | | Conversion | Cannot be fully converted into work in a cycle (Kelvin-Planck) | Can be fully converted to heat (e.g. friction) | | Sign (standard) | Heat added to system +ve | Work done by system +ve | | Symbol | Q (kJ), q = Q/m | W (kJ), w = W/m | | Both are | Path functions; boundary phenomena; not properties | Path functions; boundary phenomena; not properties | Example: heating water on a stove is heat transfer; a gas pushing a piston outward is work transfer. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Heat transfer is caused by A. a force through a distance B. a voltage difference C. a temperature difference D. a pressure difference Answer: C. Heat is energy crossing the boundary because of a temperature difference. (Key point: Cause) 2. Heat is regarded as __ energy transfer, while work is __. A. organised; disorganised B. disorganised; organised C. organised; organised D. disorganised; disorganised Answer: B. Heat is random molecular motion; work is ordered motion. (Key point: Nature of energy) 3. Which statement is true? A. Work can be fully converted to heat, e.g. by friction B. Heat can be fully converted to work in a cycle C. Neither is convertible D. Both are fully convertible Answer: A. Kelvin-Planck prevents full conversion of heat to work in a cycle; friction fully converts work to heat. (Key point: Convertibility) 4. What do heat and work have in common? A. Both are properties B. Both are state functions C. Both are path functions and boundary phenomena D. Both need a temperature difference Answer: C. Both depend on the path, occur at the boundary and are not properties. 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