Himself thought that something else besides total energy was conserved: theīut we know better: in a Carnot cycle, the heat leaving the gas on theĮntering earlier, by just the amount of work performed. Of the gas is the same at the end of the cycle as it was at the beginning, but ![]() We know, of course, one thing that doesn’t change: the internal energy To get a clue about what stays the same in a reversibleĬycle, let’s review the Carnot cycle once more. Heat Changes along Different Paths from a to c Labeled entropy that doesn’t change in a reversible process, but always Parameter? The answer turns out to be yes: there is a parameter Clausius The “amount of irreversibility” to be measured? Does it correspond to some thermodynamic Reversible engine has to equal that of the Carnot cycle, and any nonreversible The second law, that heat only flows from a warmer body to aĬolder one, does have quantitative consequences: the efficiency of any Other names, but those are merely notational developments.) Work, the unit wasn’t called a Joule, and the different types of energy had Up to get the total and that will remain constant. Heat units and energy units, calories to joules, since all the other types ofĮnergy (kinetic, potential, electrical, etc.) are already in joules, add it all His aim was to express both laws in aĬonservation of total energy including heat energy -is easy toĮxpress quantitatively: one only needs to find the equivalence factor between So what, exactly, is entropy, where did this word comeĬlausius in 1865, a few years after he stated the laws of thermodynamics This was called the Heat Death of the Universe, and may still be what’sīelieved, except that now everything will also be flying further and further Used to describe the approach to an imagined final state of the universe whenĮverything reaches the same temperature: the entropy is supposed to increase toĪ maximum, then nothing will ever happen again. Synonym for chaos, for example: the entropy in my room increases as the The word “entropy” is sometimes used in everyday life as a The term used to describe this distribution is called entropy.Previous index next A New Thermodynamic Variable: Entropy How the energy and atoms are distributed in the reactants and products are just as important as the energy released or absorbed. Obviously, there is another factor than energy to consider when deciding if a reaction is product- or reactant-favored. Another example is the mixing of ammonium chloride and barium hydroxide, which absorbs enough energy from the surroundings to freeze a beaker to a wet board (click on the image at right to see the reaction).īa(OH) 2 8 H 2O (s) + 2 NH 4Cl (s) BaCl 2 2 H 2O (s) + 2 NH 3 (aq) + 8 H 2O ( l) Is obviously product-favored, even though the reaction is endothermic. For example, the melting of solid ice to liquid water at 25 ✬: There were some striking exceptions, however. The combustion of gasoline and the production of table salt, for example, have DH fº values of -10.452.3 kJ and -822.306 kJ, respectively. For example the production of table salt from sodium metal and chlorine gas is a product-favored reaction:Įarly on, chemists noticed that most product-favored reactions were exothermic. Second, the reverse of every reactant-favored reaction is a product-favored reaction. Two important things to remember about reactant-favored reactions: they can be forced to produce products if energy, such as heat, electricity, or some other form, is continuously supplied. For example, the formation of sodium metal and chlorine gas from table salt is a reactant-favored process: ![]() On the other hand, a reactant-favored reaction is one in which reactants are more predominant than products. For example, the combustion of gasoline (mostly octane) in your car engine is a product-favored reaction:Ģ C 8H 18 (g) + 25 O 2 (g) 16 CO 2 (g) + 18 H 2O (g) A reaction is called product-favored if, after the reaction is over, there are more products than reactants. This question can be partially answered by thermodynamics. Use the Second Law of Thermodynamics to predict whether a reaction will be product- or reactant-favored.Ī major goal of chemistry is predicting what reactions will occur and under what conditions. ![]() Describe how probability is the cause of the Second Law of Thermodynamics.When you have completed this module, you should be able to:
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