Entropy is a measure of the degree of disorder in a system and the dispersion of energy. Over time, energy in a system naturally changes to less useful forms, leading to an increase in entropy in accordance with the second law of thermodynamics.
The relationship between entropy and energy
Thermodynamics vs. entropy: entropy and energy are closely related in the context of thermodynamics. Entropy (S) is a measure of the dispersion of energy in a system. When energy is evenly distributed, entropy increases.
The first law of thermodynamics states that energy in a system is conserved (cannot be created or destroyed, only transformed).
The second law of thermodynamics states that the entropy of an isolated system always increases or remains constant – it never decreases. This means that energy has a natural tendency to change into less useful forms (e.g. heat).
Thermal energy vs. entropy: if we heat a body, its molecules start to move faster, increasing disorder and therefore entropy. When ice melts, it absorbs energy from its surroundings, which increases entropy. When a gas expands in a vacuum, its entropy increases because the molecules spread out over a larger volume.
Entropy and the decay of energy in space: on the scale of the Universe, energy is constantly changing into forms of higher entropy – this leads to the concept of the heat death of the Universe, where all energy will be dissipated as heat at a uniform temperature and physical processes will cease.
Examples of entropy in everyday life
Entropy is all around us, even if we don’t always notice it. Here are some examples from everyday life that show how it works:
Clutter in a space – lack of regular cleaning means that space becomes increasingly chaotic over time – documents, books and objects don’t sort themselves out. This is an example of a natural increase in entropy. To reduce entropy, you have to put in energy (i.e. clean up).
Aging and decomposition of organisms – bodies undergo degradation processes – cells lose their ability to repair themselves, organic matter disintegrates after death, and the body enters a state of higher entropy.
Hot coffee cools – leaving hot coffee on the table causes its temperature to gradually equalize with the surroundings. The heat energy dissipates and the system enters a state of higher entropy because the temperature difference disappears.
Spreading of scents – when perfume is sprayed, scent molecules quickly spread throughout the room. Initially they are concentrated in one place, but over time entropy increases and the smell spreads evenly in the air.
Fuel combustion – a vehicle consumes fuel, converting its ordered chemical energy into heat, motion, and exhaust. Some of the energy is used for propulsion, but most of it is dissipated as heat, which increases entropy.
Entropy is a universal process – without a constant supply of energy, everything gradually becomes more disordered.