The overall reaction that occurs when sugar is
For this reaction, ΔH° is -5650 kJ and ΔG° is -5790 kJ at 25°C.
(a) If 25% of the free energy change is actually converted to useful work, how many kilojoules of work are obtained when one gram of sugar is metabolized at body temperature, 37°C?
(b) How many grams of sugar would a 120-lb woman have to eat to get the energy to climb the Jungfrau in the Alps, which is 4158 m high? (
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Chapter 16 Solutions
Chemistry: Principles and Reactions
- For the reaction NO(g)+NO2(g)N2O3(g) , use tabulated thermodynamic data to calculate H and S. Then use those values to answer the following questions. (a) Is this reaction spontaneous at 25°C? Explain your answer. (b) If the reaction is not spontaneous at 25°C, will it become spontaneous at higher temperatures or lower temperatures? (c) To show that your prediction is accurate, choose a temperature that corresponds to your prediction in part (b) and calculate G . (Assume that both enthalpy and entropy are independent of temperature.)arrow_forwardWhat is the sign of the work when a refrigerator compresses a gas (the system) to a liquid during the refrigeration cycle?arrow_forwardEthanol burns in air or oxygen according to the equation C2H5OH(l)+3O2(g)2CO2(g)+3H2O(g) Predict the sign of S for this reaction.arrow_forward
- Many biochemical reactions that occur in cells require relatively high concentrations of potassium ion (K+). The concentration of K + in muscle cells is about 0.l5 M. The concentration of K+ in blood plasma is about 0.0050 M. The high internal concentration in cells is maintained by pumping K+ from the plasma. How much work must be done to transport 1.0 mole of K+ from the blood to the inside of a muscle cell at 37C, normal body temperature? When 1.0 mole of K+ is transferred from blood to the cells, do any other ions have to be transported? Why or why not?arrow_forwardIdentify the sign of the work when a fuel-oxygen mixture (the system) burns, propelling an automobile (part of the surroundings).arrow_forwardDetermine whether each of the following statements is true or false. (a) An exothermic reaction is spontaneous. (b) When G° is positive, the reaction cannot occur under any conditions. (c) S° is positive for a reaction in which there is an increase in the number of moles. d) If H° and S° are both negative, G° will be negative.arrow_forward
- Consider the reaction of 2 mol H2(g) at 25C and 1 atm with 1 mol O2(g) at the same temperature and pressure to produce liquid water at these conditions. If this reaction is run in a controlled way to generate work, what is the maximum useful work that can be obtained? How much entropy is produced in this case?arrow_forwardCoal 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.arrow_forwardHow is the sign of q, heat, defined? How does it relate to the total energy of the system?arrow_forward
- Define the following: a. spontaneous process b. entropy c. positional probability d. system e. surroundings f. universearrow_forwardNickel metal reacts with carbon monoxide to form tetra-carbonyl nickel, Ni(CO)4: Ni(s)+4CO(g)Ni(CO)4(g) This reaction is exploited in the Mond process in order to separate pure nickel from other metals. The reaction above separates nickel from impurities by dissolving it into the gas phase. Conditions are then changed so that the reaction runs in the opposite direction to recover the purified metal. (a) Predict the sign of S for the reaction as written above. (b) Use tabulated thermodynamic data to calculate H, S , and G for the reaction. (c) Find the range of temperatures at which this reaction is spontaneous in the forward direction.arrow_forward
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