4. The second law of thermodynamics states that A. the total energy change of the universe is always positive. B. the total entropy change of the universe is positive in a spontaneous process. C. the total energy of the universe is always constant. D. there is no disorder in a perfect crystal at 0 K. E. mass and energy are conserved in all chemical reactions.

Coal is used as a fuel in some electric-generating plants. Coal is a complex material, but for simplicity we may consider it to be a form of carbon. The energy that can be derived from a fuel is sometimes compared with the enthalpy of the combustion reaction: C(s)+O2(g)CO2(g) Calculate the standard enthalpy change for this reaction at 25C. Actually, only a fraction of the heat from this reaction is available to produce electric energy. In electric generating plants, this reaction is used to generate heat for a steam engine, which turns the generator. Basically the steam engine is a type of heat engine in which steam enters the engine at high temperature (Th), work is done, and the steam then exits at a lower temperature (Tl). The maximum fraction, f, of heat available to produce useful energy depends on the difference between these temperatures (expressed in kelvins), f = (Th Tl)/Th. What is the maximum heat energy available for useful work from the combustion of 1.00 mol of C(s) to CO2(g)? (Assume the value of H calculated at 25C for the heat obtained in the generator.) It is possible to consider more efficient ways to obtain useful energy from a fuel. For example, methane can be burned in a fuel cell to generate electricity directly. The maximum useful energy obtained in these cases is the maximum work, which equals the free-energy change. Calculate the standard free-energy change for the combustion of 1.00 mol of C(s) to CO2(g). Compare this value with the maximum obtained with the heat engine described here.

Define the term entropy, and give an example of a sample of matter that has zero entropy. What are the units of entropy? How do they differ from the units of enthalpy?

The statement Energycan beneithercreatednor destroyedis sometimes used as an equivalent statement of the first law of thermodynamics. There areinaccuracies to the statement, however. Restate it tomake it less inaccurate.

Consider the system shown in Figure 16.9. What is the change in entropy for the process where the energy is initially associated only with particle A, but in the final state the energy is distributed between two different particles?

Some say that the job of an engineer is to fight nature and the tendencies of entropy. (a) Does this statement seem accurate in any way? (b) How can any engineering design create order without violating the second law of thermodynamics?

9.42 Why is enthalpy generally more useful than internal energy in the thermodynamics of real world systems?

Water gas, a mixture of H2 and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon: C(s)+H2O(g)CO(g)+H2(g). (a) Assuming that coke has the same enthalpy of formation as graphite, calculate H298 for this reaction. (b) Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas and additional hydrogen at high temperature and pressure in the presence of a suitable catalyst: 2H2(g)+CO(g)CH2OH(g). Under the conditions of the reaction, methanol forms as a gas. Calculate for this reaction and for the condensation of gaseous methanol to liquid methanol. (c) Calculate the heat of combustion of 1 mole of liquid methanol to H2O(g) and CO2(g).

What is entropy? Why is entropy important?

9.72 Although it can be a nuisance when a laptop computer freezes up and needs to be rebooted, we accept that as somewhat inevitable. But clearly the need to occasionally reboot the control system for the power grid would not be acceptable. Use the web to research ways that engineers ensure the reliability of crucial systems like the control infrastructure of the grid, and write a paragraph summarizing the main strategies employed.