--- title: "Thermodynamic process; constant pressure heating diagrams" subject: "Fundamental of Thermodynamics & Heat Transfer" chapter: 1 key: "semester_2/fundamental_of_thermodynamics_and_heat_transfer:process-sketch-constant-pressure-heating" source: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/process-sketch-constant-pressure-heating site: BCT Engineering --- # Thermodynamic process; constant pressure heating diagrams Fundamental of Thermodynamics & Heat Transfer · Chapter 1: Introduction - Asked in: 2068 Magh, 4 marks - Video: [PV diagrams - part 1: Work and isobaric processes | Chemical Processes | MCAT | Khan Academy](https://www.youtube.com/watch?v=Xcrco59p40o) — khanacademymedicine - 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/process-sketch-constant-pressure-heating - Whole chapter: https://www.bctengineer.com/md/semester_2/fundamental_of_thermodynamics_and_heat_transfer/chapter-1 ## Question Define thermodynamic process. Sketch P-V, T-V, and P-T diagrams for an ideal gas undergoing constant pressure heating process. ## Short answer A thermodynamic process is the path of successive equilibrium states a system passes through. For constant-pressure heating of an ideal gas: P-V diagram is a horizontal line; T-V is a straight line through origin; P-T is a horizontal line. ## Answer A **thermodynamic process** is the path of successive states through which a system passes when it changes from one equilibrium state to another, e.g. constant pressure (isobaric), constant volume, constant temperature, adiabatic. #### Constant-pressure heating of an ideal gas Here P = constant, so from PV = mRT, V/T = constant: V ∝ T. Volume increases as the gas is heated. ```text P-V diagram T-V diagram P-T diagram P| T| / P| | 1 ------> 2 | / 2 | 1 ------> 2 | | / | | | / 1 | +--------- V +--------- V +--------- T horizontal line straight line horizontal line through origin ``` - P-V: horizontal straight line from V₁ to V₂ (V₂ > V₁); area under it = P(V₂ − V₁) = work done. - T-V: straight line passing through the origin (Charles' law). - P-T: horizontal straight line parallel to the T axis. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A thermodynamic process is A. a single equilibrium state B. the heat added to a system C. the path of successive states between two equilibrium states D. a property of the boundary Answer: C. It is the series of states a system passes through while changing from one equilibrium state to another. (Key point: Definition of process) 2. For constant-pressure heating of an ideal gas, V and T are related by A. V is constant B. V is proportional to T C. V is inversely proportional to T D. V is proportional to T^2 Answer: B. From PV = mRT at constant P, V/T is constant (Charles' law). (Key point: Constant-pressure relation) 3. On a P-V diagram the process appears as A. a vertical line B. a hyperbola C. a line through the origin D. a horizontal line Answer: D. P is constant, so the line is horizontal, with area P(V2 - V1) equal to work. (Key point: P-V diagram) 4. On a T-V diagram the process appears as A. a straight line through the origin B. a horizontal line C. a vertical line D. a hyperbola Answer: A. T is proportional to V, giving a straight line through the origin. 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