Based on the thermodynamic properties provided for water, determine the amount of energy released for 180.0 g of water to go from 18.0°C to -39.0 °C. Property Value Units Melting point 0.0 Boiling point 100.0 గి గి °C °C AHrus 6.01 kJ/mol AHvap 40.67 kJ/mol (s) 37.1 J/mol - °C S0 75.3 J/mol. °C 33.6 J/mol - °C KJ

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.

Thermodynamics provides a way to interpret everyday occurrences. If you live in northern climates, one common experience is that during early winter, snow falls but then melts when it hits the ground. Both the formation and the melting happen spontaneously. How can thermodynamics explain both of these seemingly opposed events?

A student is asked to calculate the amount of heat involved in changing 10.0 g of liquid bromine at room temperature (22.5C) to vapor at 59.0C.To do this, one must use Tables 8.1 and 8.2 for information on the specific heat, boiling point, and heat of vaporization of bromine. In addition, the following step-wise process must be followed. (a) Calculate H for: Br2(l,22.5C)Br2(l,59.0C) (b) Calculate H for: Br2(l,59.0C)Br2(g,59.0C) (c) Using Hess's law, calculate H for: Br2(l,22.5C)Br2(g,59.0C)

9.54 The phase change between graphite and diamond is difficult to observe directly. Both substances can be hurned, however. From these equations, calculate H for the conversion of diamond into graphite. C(s,graphite)+O2(g)CO2(g) H= -393.51 kJ C(s,diamond)+O2(g)CO2(g) H= -395.94 kJ

9.100 Two baking sheets are made of different metals. You purchase both and bake a dozen cookies on each sheet at the same time in your oven. You observe that after 9 minutes, the cookies on one sheet are slightly burned on the bottom, whereas those on the other sheet are fine. (You are curious and you vary the conditions so you know the result is not caused by the oven.) (a) How can you use this observation to infer something about the specific heat of the materials in the baking sheets? (b) What is themathematical reasoning (equation) that you need to support your conclusion?

9.49 Hvap=31.3 kJ/mol for acetone. If 1.40 kg of water were vaporized to steam in a boiler, how much acetone (in kg) would need to be vaporized to use the same amount of heat?

Calculate H for the reaction N2H4(l)+O2(g)N2(g)+2H2O(l) given the following data: Equation H(KJ) 2NH3(g)+3N2O(g)4N2(g)+3H2O(l) 1010 N2O(g)+3H2(g)N2H4(l)+H2O(l) 317 2NH3(g)+12O2(g)N2H4(l)+H2O(l) 143 H2(g)+12O2(g)H2O(l) 286

The enthalpy of combustion of CH4(g) when H2O (1) is formed is 891 kJ/mol and the enthalpy of combustion of CH4(g) when H2O(g) is formed is 803 kJ/mol. Use these data and Hesss law to determine the enthalpy of vaporization for water.

The enthalpy change for the reaction CH4(g)+2O2(g)CO2(g)+2H2O(l) is 891 kJ for the reaction as written. a. What quantity of heat is released for each mole of water formed? b. What quantity of heat is released for each mole of oxygen reacted?