Thermochemistry - Entropy

As mentioned much earlier, two quantities determine whether a reaction will be spontaneous or not, the thermal energy and disorder. Disorder is also known as entropy. Entropy is given the symbol S. In general, entropy always has a tendency to increase. In other words, the universe has a tendency to move towards disorder. When disorder increases, we say entropy increases. An increase in entropy is assigned a positive sign. When order increases, we say entropy decreases. A decrease in entropy is assigned a negative sign. Entropy only has a zero value if we consider a perfect crystal at absolute zero. Since it is not possible to reach absolute zero, no substance has a value of zero entropy.