Question 1

Petroleum refining – primary fractions obtained by distillation Crude (natural) petroleum can be separated into which of the following principal fractions?

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Introduction / Context: Crude oil is a complex mixture of hydrocarbons that is separated in refineries by fractional distillation and subsequent processing. Recognizing the main product streams is foundational for energy engineering and industrial chemistry. Given Data / Assumptions: Atmospheric and vacuum distillation towers are used. Products are grouped by boiling-range cuts. Further conversion (cracking, reforming) can adjust yields and qualities. Concept / Approach: At atmospheric pressure, lighter fractions such as gases (LPG), naphtha/petrol (gasoline), kerosene, and diesel are withdrawn at various trays. Heavier residues proceed to vacuum distillation to yield heavy gas oils, fuel oils, and base stocks for lubricating oils and bitumen. Therefore, petrol, kerosene, fuel oil, and lubricating oil are all legitimate fractions obtained from crude. Step-by-Step Solution: Identify separation method: fractional distillation by boiling range.List common fractions: LPG/naphtha (petrol), kerosene/jet, gasoil/diesel, heavy fuel oils, lube distillates, residues.Match with options: petrol, kerosene, fuel oil, and lubricating oil all appear in standard refinery slates.Therefore select “all of the above.” Verification / Alternative check: Refinery flow diagrams consistently show draw-offs corresponding to these fractions, sometimes with regional naming differences (gasoline/petrol, furnace oil/fuel oil). Why Other Options Are Wrong: None individually capture the complete list; the refinery yields all of them, making “all of the above” the only fully correct choice. Common Pitfalls: Confusing primary distillation products with cracked or reformed products; while upgrading units change compositions, the principal fractions remain as listed. Final Answer: all of the above

Question 2

Thermodynamic terms – naming the region where a process occurs A defined quantity of matter or a region in space selected for analysis, within which a thermodynamic process takes place, is called a:

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Introduction / Context: Clear terminology is essential in thermodynamics. We must distinguish among system, surroundings, process, and cycle. This question asks you to identify the correct term for the “definite area or space” where analysis is focused and processes occur. Given Data / Assumptions: A boundary separates the chosen entity from its surroundings. The entity can be a fixed mass (closed system) or a control volume (open system). Processes may involve heat and work interactions across the boundary. Concept / Approach: A thermodynamic system is the matter or region in space under study. When mass can cross the boundary it is called an open system or control volume; when mass is fixed it is a closed system. A process is the path between states, and a cycle is a sequence of processes returning to the initial state. The laws of thermodynamics provide the governing principles but are not “regions.” Step-by-Step Solution: Identify the phrase “definite area or space where a process takes place.”Map this to the term used in textbooks: system (including control volume as a system type).Therefore, the correct choice is “thermodynamic system.” Verification / Alternative check: Control-volume analyses of turbines, compressors, and nozzles treat the device interior region as the system. Piston–cylinder analyses treat the confined gas (fixed mass) as the system—consistent with the same overarching definition. Why Other Options Are Wrong: Cycle: a closed sequence of processes, not the region. Process: the transformation between states, not the entity itself. Law: a governing principle, not a physical region. Control chart: unrelated term from quality management, not thermodynamics. Common Pitfalls: Using “control volume” and “system” as if mutually exclusive; in thermodynamics, a control volume is a type of system (open system). Final Answer: thermodynamic system

Question 3

Thermodynamic Property Classification – Identify Specific Volume In engineering thermodynamics, the specific volume v (volume per unit mass) describes how much volume is occupied by a unit mass of a substance at a given state. Specify whether specif…

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Introduction / Context: Correctly classifying properties as intensive or extensive is foundational for applying mass and energy balances, formulating equations of state, and scaling processes. Specific volume, denoted v, is widely used in steam tables, gas tables, and compressible-flow relations, so knowing its category prevents conceptual mistakes. Given Data / Assumptions: Specific volume v is defined as V/m, where V is total volume and m is total mass. System can be subdivided into non-overlapping parts without changing local thermodynamic state. We are considering equilibrium states (uniform properties within each part). Concept / Approach: An extensive property scales with system size and is additive over subsystems (e.g., total mass, total volume, total internal energy). An intensive property does not scale with system size and remains the same for subsystems at the same state (e.g., temperature, pressure, density). Since specific volume is the ratio V/m, it is independent of the overall size of the system at a fixed state, hence intensive. Equivalently, density rho = 1/v is also intensive. Step-by-Step Solution: Start with the definition: v = V/m.Consider doubling system size: V → 2V and m → 2m.Compute the ratio: v_new = (2V)/(2m) = V/m = v.Conclude v does not depend on system size → intensive property. Verification / Alternative check: Tabulated thermodynamic property data (e.g., steam tables) list v alongside p and T. When a uniform system is split into equal halves at identical p and T, each half has the same v as the original, confirming intensiveness. Meanwhile, total volume V halves and mass m halves—both extensive—yet v remains unchanged. Why Other Options Are Wrong: 'Extensive' is incorrect because extensive properties scale with size; v does not. 'State-dependent but neither' is vague and ignores standard definitions. 'Path property' conflates state functions with process-dependent quantities; v is a state property. 'Extrinsic only for solids' is meaningless here; intensiveness is not restricted by phase. Common Pitfalls: Confusing specific properties (per unit mass) with total properties; assuming any property involving volume must be extensive. Remember: ratios of extensive properties (like V/m) typically yield intensive properties. Final Answer: intensive

Question 4

Polytropic Relation Identification – Special Case n = 1 For a perfect gas undergoing a polytropic process described by p * v^n = C, determine whether the case n = 1 corresponds to an isothermal process (constant temperature).

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Introduction / Context: Recognizing special cases of the polytropic relation p * v^n = C is a standard skill in thermodynamics and compressible flow. The correct identification helps select the right equations for work, heat transfer, and state changes during compression or expansion of gases. Given Data / Assumptions: Working fluid behaves as an ideal (perfect) gas in the process. Polytropic relation: p * v^n = constant, with exponent n specifying the path. Quasi-static process so that p and v are well-defined state variables along the path. Concept / Approach: For an ideal gas, the equation of state is p * v = R * T (on a per-unit-mass basis). If the polytropic exponent n equals 1, then p * v^1 = constant implies p * v = constant. Combining with p * v = R * T gives R * T = constant, hence T = constant. Therefore, the polytropic case n = 1 coincides with an isothermal process for an ideal gas. Other important special cases include n = 0 (isobaric), n → ∞ (isochoric), and n = gamma (isentropic for a perfect gas with constant specific heats). Step-by-Step Solution: Start from p * v^n = C.Set n = 1 → p * v = C.Use ideal-gas EOS: p * v = R * T.Therefore R * T = C → T = constant → isothermal. Verification / Alternative check: On a T–s diagram, an isothermal path for an ideal gas has constant temperature; consistency is also seen on a p–v plot where n = 1 polytrope is a rectangular hyperbola, matching the classic isotherm shape for ideal gases. Why Other Options Are Wrong: Conditions like 'only at low pressure' or 'only if no heat transfer' are unnecessary; isothermal processes do require heat exchange to keep T constant during compression/expansion, but the identification n = 1 remains valid for ideal gases without those extra caveats. Common Pitfalls: Confusing isothermal with isentropic; for an ideal gas, isentropic requires n = gamma, not 1. Also, mixing up the behavior of real gases at high pressures where EOS deviations occur (outside the scope here). Final Answer: True

Question 5

Cycle Recognition – Two Isothermal and Two Constant-Pressure Processes A thermodynamic cycle that comprises two isothermal processes (heat addition and heat rejection) and two constant-pressure regenerative processes is known as the Ericsson cycle. …

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Introduction / Context: Identifying classic ideal cycles from their process makeup helps in selecting appropriate analysis methods and understanding performance limits. The Ericsson cycle is frequently compared with Carnot, Stirling, and Joule (Brayton) cycles, so clarity about its component processes is essential. Given Data / Assumptions: Ideal, fully reversible processes with perfect regeneration. Working fluid approximated as an ideal gas with constant properties. Heat addition/removal executed isothermally; internal heat exchange executed at constant pressure. Concept / Approach: The Ericsson cycle consists of two isothermal legs (compression at the lower temperature and expansion at the higher temperature) and two isobaric regenerative legs. The isobaric legs transfer heat internally between the hot and cold streams in a regenerator, enabling the cycle to approach Carnot efficiency under ideal conditions. By contrast, the Stirling cycle uses isothermal legs plus two constant-volume (isochoric) regenerative legs, and the Joule (Brayton) cycle uses two isentropic legs with two constant-pressure heat-transfer legs to external reservoirs (not regenerative by definition). Step-by-Step Solution: List Ericsson processes: isothermal compression at T_L → isobaric regeneration heating → isothermal expansion at T_H → isobaric regeneration cooling.Confirm two isothermal + two isobaric regenerative legs.Match this set uniquely to the Ericsson cycle.Therefore, the statement is correct. Verification / Alternative check: Graphically, T–s shows two horizontal isotherms linked by near-horizontal isobars (with regeneration), whereas Stirling would show vertical isochores for the regenerative legs. Textbook definitions align with this process identification. Why Other Options Are Wrong: Calling it Stirling confuses isobaric with isochoric regeneration. Restricting to 'open cycles' is unnecessary. While perfect regeneration is an idealization, the cycle definition itself is indeed two isothermal plus two isobaric processes. Common Pitfalls: Mixing Ericsson and Brayton; assuming any constant-pressure legs imply Brayton rather than recognizing the isothermal legs that define Ericsson. Final Answer: True

Question 6

Reversibility with Regeneration – Which Process Types Can Be Rendered Reversible? With an ideal regenerator (perfect internal heat exchanger), which of the following process types in closed-system cycles can, in principle, be executed reversibly by …

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Introduction / Context: Heat-transfer irreversibility often arises from finite temperature differences between a system and an external reservoir. A regenerator exchanges heat internally between hot and cold streams, potentially eliminating those finite differences and thereby making the heat transfer reversible. This idea underlies ideal Stirling (isochoric regeneration) and Ericsson (isobaric regeneration) cycles, and it can be generalized conceptually. Given Data / Assumptions: Idealized, perfectly efficient regenerator (no pressure drop, no heat loss, infinite effectiveness). Quasi-static processes with no mechanical friction or mixing losses. Working fluid approximated as an ideal gas over the range of interest. Concept / Approach: If the heat required during a process leg is supplied or removed internally at the same temperature as the system at each instant, then the temperature difference driving heat transfer is infinitesimal, so entropy generation due to heat transfer is zero. This logic applies not only to constant-pressure or constant-volume legs but also to appropriately guided polytropic paths, provided the regenerator can match the system temperature path on the opposite leg. Thus, regeneration offers a mechanism to make these heat-transfer legs internally reversible in the ideal limit. Step-by-Step Solution: Identify heat-addition and heat-rejection legs in a candidate cycle.Route hot effluent through a regenerator matrix to store heat at temperatures matching the departing stream.On the return leg, recover that stored heat at matching temperatures, making ΔT at the interface infinitesimal.Conclude that CP, CV, and suitably planned polytropic legs can be made reversible with ideal regeneration. Verification / Alternative check: Stirling cycle (isothermal plus two isochoric regenerative legs) and Ericsson cycle (isothermal plus two isobaric regenerative legs) are textbook demonstrations. Polytropic recuperation is used industrially (recuperated Brayton) to reduce exergy destruction; the idealized limit corresponds to reversible internal heat exchange. Why Other Options Are Wrong: Choosing only one leg ignores the generality of the regenerative concept. 'None of these' contradicts well-established ideal cycles that are fully reversible with perfect regeneration. Common Pitfalls: Assuming regeneration eliminates all irreversibilities automatically—mechanical friction and pressure drops must also be minimized. Also, real regenerators have finite effectiveness, so practical processes remain slightly irreversible. Final Answer: all of these

Question 7

Petroleum Processing – Name the Operation: High-Temperature, High-Pressure Heating of Crude What is the process called in petroleum refining where crude oil (or heavy fractions) is heated to high temperature under high pressure to break large hydroc…

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Introduction / Context: Modern refineries tailor product slates by converting heavy hydrocarbons into lighter, higher-value products. The key conversion route uses heat (and sometimes catalysts) to break carbon–carbon bonds in long-chain molecules, increasing gasoline and middle distillate yields. Identifying this operation is basic refinery knowledge. Given Data / Assumptions: Feed: crude oil or heavy fractions (e.g., gas oils, residues). Operating conditions: elevated temperature; often elevated pressure (especially in thermal cracking). Goal: increase yield of lighter fractions. Concept / Approach: Cracking is the general term for processes that cleave large hydrocarbons into smaller molecules. Thermal cracking uses heat (and pressure) alone; catalytic cracking adds zeolitic catalysts at moderate pressures and high temperatures to improve selectivity and lower severity. By contrast, fractional distillation merely separates components by boiling point without chemical change, and carbonisation pertains to coal pyrolysis rather than petroleum refining. Step-by-Step Solution: Identify objective: molecular breakdown to lighter products.Match to process family: cracking (thermal or catalytic).Eliminate non-conversion processes (distillation) and unrelated coal processes (carbonisation).Conclude the correct name is 'cracking'. Verification / Alternative check: Process-flow diagrams for refineries show cracking units (fluid catalytic cracking, hydrocracking, visbreaking) as primary conversion steps producing gasoline-range and middle distillates, consistent with the description. Why Other Options Are Wrong: Carbonisation applies to coal, not crude oil. Fractional or 'full' distillation separates but does not convert. Reforming changes structure (e.g., naphtha to aromatics) but does not primarily target chain scission to boost overall light-yield from heavy feeds. Common Pitfalls: Confusing cracking with reforming or isomerization; assuming pressure alone defines the operation—temperature and catalytic environment are just as crucial. Final Answer: cracking

Question 8

Molecularity Terminology – What Do You Call a One-Atom Molecule? In basic chemistry and kinetic theory, a molecule that consists of a single atom (for example, He, Ne, or Ar in the gaseous state) is termed as which type of molecule?

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Introduction / Context: Describing substances by the number of atoms per molecule (molecularity in the informal sense) is useful in thermodynamics, spectroscopy, and reaction kinetics. Noble gases exist as single, discrete atoms under standard conditions, so recognizing the correct term aids in interpreting specific heats and transport properties. Given Data / Assumptions: Molecule contains exactly one atom. Ideal-gas behavior assumed for simple property discussions. Examples include He, Ne, Ar (noble gases), and atomized metals at very high temperatures. Concept / Approach: Single-atom molecules are termed monoatomic (sometimes written monatomic). Diatomic molecules have two atoms (e.g., O2, N2), triatomic have three (e.g., CO2, H2O), and polyatomic is a broader term for more than two atoms. This classification affects degrees of freedom and hence specific heat values at a given temperature range (e.g., monoatomic ideal gases have Cv ≈ 3/2 R, Cp ≈ 5/2 R under calorically perfect assumptions). Step-by-Step Solution: Identify the count: one atom per molecule.Map to terminology: 'monoatomic' corresponds to one atom.Check examples: He, Ne, Ar are monoatomic gases at STP.Confirm selection against other terms (diatomic, triatomic, polyatomic). Verification / Alternative check: Thermodynamic tables list specific heats for monoatomic gases consistent with 5/2 R at moderate temperatures, supporting the monoatomic classification. Why Other Options Are Wrong: Diatomic, triatomic, and tetratomic imply 2, 3, and 4 atoms per molecule, respectively. 'Polyatomic' is a generic term for many-atom molecules, not a single-atom case. Common Pitfalls: Confusing atomic number with atoms per molecule; misclassifying halogens (e.g., Cl2) as monoatomic—many elemental gases are diatomic, not monoatomic. Final Answer: monoatomic

Thermodynamics Questions