The universe maintains a strict and perfect energy accounting system
In short: Energy cannot be created or destroyed, only moved or transformed. The First Law of Thermodynamics treats the universe like a bank account where every deposit of heat and every withdrawal of work must perfectly balance. To understand how machines, chemicals, and life function, we must master this cosmic ledger.
The First Law of Thermodynamics establishes that the total energy of the universe remains constant. This concept holds that the combined energy of a system and its environment stays constant, provided heat is viewed as energy. In chemistry and physics, this is visualized by tracking the flow of energy across a boundary. Scientists distinguish between three types of environments: open systems, closed systems, and isolated systems, each defining how much energy or matter can cross that boundary.
At the heart of this law is the relationship between internal energy (U), heat (Q), and work (W). Internal energy is a 'state function,' meaning its value depends only on the current state of a system at equilibrium, not on how it got there. The change in internal energy (ΔU) is calculated by the difference between the final and initial states. In contrast, heat and work are not state functions; they are 'path functions.' This means the specific amount of heat absorbed or work performed depends entirely on the specific process or path taken to reach a destination.
Consider a gas expanding in a cylinder with a movable piston. If the gas expands, it does work (W) against the piston's force. If it also absorbs heat (Q) from the surroundings, the net flow of energy across the boundary is represented as W - Q. To conserve energy, there must be a counterbalancing change in the internal energy: ΔU = Q - W. This is analogous to a bank account: the final balance (ΔU) remains the same regardless of whether you reached it through many small deposits and withdrawals or one large transaction. In chemistry, this allows us to distinguish between exothermic processes, where heat flows out of the system, and endothermic processes, where heat flows in.
Internal energy is a state function determined by initial and final states.
The change in internal energy is calculated as ΔU = Q - W. Work is positive when done on a system and negative when done by the system. Exothermic processes involve heat flowing out of the system. Endothermic processes involve heat flowing into the system. canvas
Opens the Intellect+ feed with this card first. Swipe up for the next one.
Sources
- Summary by Intellect · source: First Law of Thermodynamics, Basic Introduction - Internal Energy, Heat and Work - Chemistry
- Also: Thermodynamics - Energy, Heat, Work | Britannica
To cite this card, link to https://intellectplus.co.uk/app/science-first-law-of-thermodynamics-basic-introduction-internal-ener.
How we source, check and correct cards: Editorial standards.
General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.
Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?
Related
More in Thermodynamics · More in Science · Latest · A–Z · All topics
