636 CHAPTER 15: Chemical Thermodynamics
Exercises
General Concepts
*001.State precisely the meaning of each of the following
terms. You may need to review Chapter 1 to refresh your
memory concerning terms introduced there. (a) energy;
(b) kinetic energy; (c) potential energy; (d) joule.
*002.State precisely the meaning of each of the following
terms. You may need to review Chapter 1 to refresh your
memory about terms introduced there. (a) heat; (b) tem-
perature; (c) system; (d) surroundings; (e) thermodynamic
state of system; (f ) work.
*003.(a) Give an example of the conversion of heat into work.
(b) Give an example of the conversion of work into heat.
*004.Distinguish between endothermic and exothermic
processes. If we know that a reaction is endothermic in
one direction, what can be said about the reaction in the
reverse direction?
*005.According to the First Law of Thermodynamics, the total
amount of energy in the universe is constant. Why, then,do we say that we are experiencing a declining supply of
energy?
*006.Use the First Law of Thermodynamics to describe what
occurs when an incandescent light is turned on.
*007.Use the First Law of Thermodynamics to describe what
occurs when sunlight strikes a black surface.
*008.Which of the following are examples of state functions?
(a) your bank balance; (b) your mass; (c) your weight;
(d) the heat lost by perspiration during a climb up a moun-
tain along a fixed path.
*009.What is a state function? Would Hess’s Law be a law if
enthalpy were not a state function?Enthalpy and Changes in Enthalpy
*010.(a) Distinguish between Hand H^0 for a reaction.
(b) Distinguish between H^0 rxnand H^0 f.
*011.A reaction is characterized by Hrxn500 kJ/mol.Nonspontaneous change See Reactant-favored change.
Pressure–volume work Work done by a gas when it expands
against an external pressure or work done on a system as gases
are compressed or consumed in the presence of an external pres-
sure.
Product-favored change A change for which the collection of
products is more stable than the collection of reactants under
the given conditions; also called spontaneous change.
Reactant-favored change A change for which the collection of
reactants is more stable than the collection of products under
the given conditions; also called nonspontaneous change.
Second Law of Thermodynamics The universe tends toward
a state of greater disorder in spontaneous processes.
Spontaneous change See Product-favored change.
Standard enthalpy change, H^0 The enthalpy change in which
the number of moles of reactants specified in the balanced
chemical equation, all at standard states, is converted com-
pletely to the specified number of moles of products, all at
standard states.
Standard entropy, S^0 (of a substance) The absolute entropy
of a substance in its standard state at 298 K.
Standard entropy change, S^0 The entropy change in which
the number of moles of reactants specified in the balanced chem-
ical equation, all at standard states, is converted completely to
the specified number of moles of products, all at standard states.
Standard molar enthalpy of formation, Hf^0 (of a substance)
The enthalpy change for the formation of one mole of a sub-
stance in a specified state from its elements in their standard
states.
Standard reaction A reaction in which the numbers of moles of
reactants shown in the balanced equation, all in their standard
states, are completelyconverted to the numbers of moles of prod-
ucts shown in the balanced equation, also all at their standard
states.
Standard state (of a substance) See Thermodynamic standard
state of a substance.
State function A variable that defines the state of a system; a
function that is independent of the pathway by which a process
occurs.
Surroundings Everything in the environment of the system.
System The substances of interest in a process; the part of the
universe under investigation.
Thermochemical equation A balanced chemical equation
together with a designation of the corresponding value of Hrxn.
Sometimes used with changes in other thermodynamic quanti-
ties.
Thermodynamics The study of the energy transfers accompa-
nying physical and chemical processes.
Thermodynamic state of a system A set of conditions that
completely specifies all of the properties of the system.
Thermodynamic standard state of a substance The most sta-
ble state of the substance at one atmosphere pressure and at
some specific temperature (25°C unless otherwise specified).
Third Law of Thermodynamics The entropy of a hypotheti-
cal pure, perfect, crystalline substance at absolute zero
temperature is zero.
Universe The system plus the surroundings.
Work The application of a force through a distance; for physi-
cal changes or chemical reactions at constant external pressure,
the work done on the system is PV.