Entropy can be thought of as a measure of a system's disorder: a lower degree of disorder implies lower entropy, and vice versa. for example, a highly ordered ice crystal has a relatively low entropy, whereas the same amount of water in a much less ordered state, such as water vapor, has a much higher entropy. entropy is usually denoted by s, and has units of energy divided by temperature (j/k). for an isothermal process (the temperature of the system remains constant as it exchanges heat with its surroundings), the change in a system's entropy is given by δs=qt, where q is the amount of heat involved in the process and t is the absolute temperature of the system. the heat q is positive if thermal energy is absorbed by the system from its surroundings, and is negative if thermal energy is transferred from the system to its surroundings.