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
PRINCIPLES+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_forward9.20 State the first law of thermodynamics briefly in your own words.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_forward
- What is the sign of the work when a refrigerator compresses a gas (the system) to a liquid during the refrigeration cycle?arrow_forwardHow is the sign of q, heat, defined? How does it relate to the total energy of the system?arrow_forwardAthletic trainers use instant ice packs that can be cooled quickly on demand. Squeezing the pact breaks an inner container, allowing two components to mix and react. This reaction makes the pack become cold. Describe the heat flow for this spontaneous process.arrow_forward
- Identify the sign of the work when a fuel-oxygen mixture (the system) burns, propelling an automobile (part of the surroundings).arrow_forwardWhen a rocket is launched, the burning gases are the source of the motion. If the system is the rocket (including fuel), what is the sign of the work?arrow_forward9.53 Using these reactions, find the standard enthalpy change for the formation of 1 mol of PhO(s) from lead metal and oxygen gas. PbO(s)+C(graphite)Pb(s)+CO(g) H = 106.8 kJ 2C(graphite)+O2(g)2CO(g) H= -221.0 kJ If 250 g of lead reacts with oxygen to form lead(II) oxide, what quantity of thermal energy (in kJ) is ahsorhed or evolved?arrow_forward
- Write the balanced chemical equation for the combustion of methane, CH4(g), to give carbon dioxide and water vapor. Explain why it is difficult to predict whether S is positive or negative for this chemical reaction.arrow_forwardA pot of cold water is heated on a stove, and when the water boils, a fresh egg is placed in the water to cook. Describe the events that are occurring in terms of the zeroth law of thermodynamics.arrow_forwardNitrogen gas reacts with hydrogen gas to form ammonia gas .Consider the reaction between nitrogen and hydrogen as depicted below: a. Draw what the container will look like after the reaction has gone to completion. Assume a constant pressure of 1 atm. b. Is the sign of work positive or negative, or is the value of work equal to zero for the reaction? Explain your answer.arrow_forward
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