---
title: "Stored vs transient energy; total energy"
subject: "Fundamental of Thermodynamics & Heat Transfer"
chapter: 2
key: "semester_2/fundamental_of_thermodynamics_and_heat_transfer:stored-vs-transient-energy"
source: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/stored-vs-transient-energy
site: BCT Engineering
---

# Stored vs transient energy; total energy

Fundamental of Thermodynamics & Heat Transfer · Chapter 2: Energy and Energy Transfer

- Asked in: 2073 Magh, 4 marks; 2069 Bhadra, 4 marks (asked 2 times)
- Video: [Internal Energy and Stored Energy by Dr. S D mohanty](https://www.youtube.com/watch?v=0vkb_JVuods) — ErudiSpace
- 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/stored-vs-transient-energy
- Whole chapter: https://www.bctengineer.com/md/semester_2/fundamental_of_thermodynamics_and_heat_transfer/chapter-2

## Question

Explain the differences between stored energy and transient energy with examples. Also define total energy.

## Short answer

Stored energy is energy possessed within a system as a property (state function), e.g., internal, kinetic, potential energy. Transient energy, like heat and work, crosses the boundary during interactions, is not a property, and is path-dependent. Total energy E = U + KE + PE.

## Answer

Energy of a system exists in two ways: stored in the system (a property) or in transit across its boundary.

| Basis | Stored energy | Transient (transit) energy |
|---|---|---|
| Meaning | Energy possessed by the system within its boundary | Energy that crosses the boundary during a process |
| Is it a property? | Yes (state function) | No (path function) |
| Exists | At any state of the system | Only during the interaction |
| Differential | Exact, dE | Inexact, δQ, δW |
| Examples | Internal energy U, kinetic energy ½mV², potential energy mgz | Heat Q, work W (also energy carried by mass in open systems) |

**Example:** Hot water in a closed tank has stored internal energy. If the tank is heated through its wall, the heat Q is transient energy; once it enters, it is stored as increased internal energy. Stirring the water with a paddle is work, also transient, which then appears as stored internal energy.

#### Total energy
Total energy E of a system is the sum of all forms of energy stored in it:

**E = U + KE + PE** (+ chemical, nuclear, electrical, etc. if present)

where U = internal energy, KE = ½mV², PE = mgz. On a unit mass basis: e = u + V²/2 + gz. For a stationary system, E = U.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which is stored energy?
   A. Heat Q
   B. Work W
   C. Energy crossing the boundary
   D. Internal energy U
   Answer: D. Internal, kinetic and potential energy are possessed by the system and are properties. (Key point: Stored energy)

2. Transient energy is
   A. a property with exact differential
   B. energy that crosses the boundary during a process; a path function
   C. energy present at any state
   D. the same as total energy
   Answer: B. Heat and work exist only during the interaction and have inexact differentials. (Key point: Transient energy)

3. Total energy of a system is
   A. Q + W
   B. U - KE - PE
   C. U + KE + PE (plus other forms if present)
   D. only U
   Answer: C. E = U + KE + PE; for a stationary system E = U. (Key point: Total energy)

4. When paddle-wheel stirring work is done on a fluid in an insulated tank, it
   A. is stored as increased internal energy
   B. remains as work inside the system
   C. disappears
   D. becomes heat Q
   Answer: A. Work is transient, but once it enters it appears as stored internal energy. (Key point: Conversion to stored energy)

## Related in Fundamental of Thermodynamics & Heat Transfer

- [Nitrogen piston with stops: work and heat](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Anitrogen-piston-stops-0-2mpa-70c) — Fundamental of Thermodynamics & Heat Transfer, chapter 4

## Related in other subjects

- [Energy stored in parallel capacitors](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aparallel-capacitors-energy-stored) — Engineering Physics, chapter 7
- [Energy stored in an inductor](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aenergy-density-inductor-magnetic-field) — Engineering Physics, chapter 8, asked 4×
- [Energy stored in coil, time constants](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Acoil-energy-stored-time-constants) — Engineering Physics, chapter 8
- [Energy stored for given potential field](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Aenergy-stored-potential-field) — Electromagnetism, chapter 2