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Energy can change from one form to another, but it can be neither created nor destroyed.

The first law of thermodynamics asserts a universal conservation of energy, stated in the context of thermodynamic systems.

The phenomenon known as entropy has been formalized as the second of these three laws of thermodynamics: It is conceivable that the process would reverse so that the ink molecules would reconstitute and form once again into a black blob, but probability working in conjunction with the arrow of time predicts otherwise. You can look at this as the ink dispersing because it has experienced an increase in volume. The ink mixes with the water, at first due to the collision between the two substances, and finally due to random molecular motion. The ink will mix with the water, quickly dissipating and becoming invisible as its concentration decreases. Into a vessel of clear water, introduce a small amount of black ink. The principle can be easily demonstrated in the lab or even as a simple table-top demonstration at home. The usual ways energy spreads out is when the system increases in volume or when the system is heated. So increasingly the “disorder” explanation is giving way to the idea that entropy describes energy spreading out or dispersing. Educators increasingly feel that the concept of entropy as the disorder can be confusing. The fact that a perfect crystal of a substance at 0 K has zero entropy is sometimes called the Third Law of Thermodynamics.It was once widely taught that entropy is a measure of disorder. This is because we know that the substance has zero entropy as a perfect crystal at 0 K there is no comparable zero for enthalpy.

The reason is that the entropies listed are absolute, rather than relative to some arbitrary standard like enthalpy. Note that there are values listed for elements, unlike DH fº values for elements. The Thermodynamics Table lists the entropies of some substances at 25 ✬. Continue this process until you reach the temperature for which you want to know the entropy of a substance (25 ✬ is a common temperature for reporting the entropy of a substance). Then you can use equation (1) to calculate the entropy changes. Even though equation (1) only works when the temperature is constant, it is approximately correct when the temperature change is small. Now start introducing small amounts of heat and measuring the temperature change. Since there is no disorder in this state, the entropy can be defined as zero. Imagine cooling the substance to absolute zero and forming a perfect crystal (no holes, all the atoms in their exact place in the crystal lattice). The absolute entropy of any substance can be calculated using equation (1) in the following way.

At absolute 0 (0 K), all atomic motion ceases and the disorder in a substance is zero. On this scale, zero is the theoretically lowest possible temperature that any substance can reach. The temperature in this equation must be measured on the absolute, or Kelvin temperature scale. Using this equation it is possible to measure entropy changes using a calorimeter.

Where S represents entropy, DS represents the change in entropy, q represents heat transfer, and T is the temperature. One useful way of measuring entropy is by the following equation: