Look up the Standard Molar Entropy of CS 2(g) and multiply it by its coefficient(1)ДЎ mole( +151 J/mole-K) = +151 J/K = Standard Entropy for one mole of H 2S(g).Add the results of steps 2 and 3 for the Sum of the Standard Entropies of the products.Look up the Standard Molar Entropy of H 2S(g) and multiply by its coefficient(2)Дў mole(205.6 J/mole-K) = +411.2 J/K = Standard Entropy of 2 moles H 2S.Look up the Standard Molar Entropy of CH 4(g) and multiply by its coefficient(1)ДЎ mole ( +186.3 J/mole-K) = +186.3 J/K = Standard Entropy of one mole of CH 4.Subtract the result of step 7 from step 4 to get the Standard Change in Entropy for the reactionД§09.9 J/K - (+766 J/K) = -56.1 J/K = Delta S rx.(+151 J/K) + (+615 J/K) = +766 J/K = Sum of Standard Entropies for Reactants Add results of steps 5 and 6 to get the Sum of the Standard Entropies for the Reactants.Look up the Standard Molar Entropy of O 2(g) and multiply by its coefficient(3)ДЈ mole(+205 J/mole-K) = +615 J/K = Standard Entropy for 3 moles O 2.Look up the Standard Molar Entropy of CS 2(l) and multiply by its coeff (1)ДЎ mole ( +151 J/mole-K) = +151 J/K = Standard Entropy of one mole of CS 2(l).Add the result of steps 2 and 3 to get the Summ of the Entropies of the products.Look up the Standard Molar Entropy for SO 2 and multiply it by its coefficient(2)Дў moles(248.1 J/mole-K) = 496.2 J/K = Standard Entropy for 2 moles of SO 2.Look up the Standard Molar Entropy for CO 2(g) in the Thermodynamic Properties table found in your text and multiply it by its coefficient in the balanced equation (1).ДЎ mole (213.7 J/mole-K) = 213.7 J/K = Standard Entropy for one mole of CO 2.Check to make sure the equation is balanced.The entropy of a given system depends on its state and temperature.ДЇor a sample: S solid CO 2(g) + 2SO 2(g) Some general (practical) guidelines for determining Entropy: Standard entropy values are indicated as SВ° and are for substances at 1 bar pressure and 1 molal solution concentration. Since heat is added to the system, all entropy values are positive at temperatures above 0K. The change must be reversible and is calculated as: This point is simply used as a starting point for the measurement of entropy.Д®ntropy is then measured by determining the energy (heat) required to raise the temperature of a element from absolute zero to whatever temperature and conditions are prescribed. 0 Kelvin or absolute zero is the temperature at which atoms stop moving. The Third Law of Thermodynamics is usually stated as a definition: the entropy of a perfect crystal of an element at the absolute zero of temperature is zero. You have probably heard the phrase вЂњthe ever expanding UniverseвЂќ, although this phrase is often taken to mean our ever increasing knowledge of our Universe, it also is quite true that our Universe is expanding and this effect is entropic in nature. Coffee in cream and gas expansion and perfume in air are вЂhow widely' processes where the initial energy of the molecules stay the same but the volume occupied by the molecules increases. You see now how hot pans cooling and chemical reactions belong to the вЂhow much' category where energy is being transferred. This is reflected in the idea that a spontaneous change always results in the dispersal (spreading out) of energy (and also matter). Entropy change measures the dispersal of energy: how much energy is spread out in a particular process, or how widely spread out it becomes (at a specific temperature). The Second Law of Thermodynamics states that for a reaction to be spontaneous, there must be an increase in entropy.Д®ntropy is often defined as a measure of the disorder of a system, this is not a very accurate definition. The best indicator of spontaneity in a reaction is the change in Entropy (S or DS). The application of spontaneity with respect to equilibrium is as follows:ДЄ reaction will never spontaneously move away from equilibrium and will always move spontaneously towards equilibrium.ДЄlthough spontaneous reactions are often exothermic, this is not a criteria for spontaneity. A non-spontaneous process needs a continual input of energy.

A spontaneous process is one that, once started, continues on its own without input of energy.

Entropy chemistry