Chapter 6: Thermochemistry Flashcards
energy
the capacity to do work to cause heat flow
law of conservation of energy
energy can be converted from one form to another but can be neither created nor destroyed.
potential energy (PE)
energy due to position or composition.
kinetic energy (KE)
(1/2mv2) energy due to the motion of an object; dependent on the mass of the object and the square of its velocity
heat
energy transferred between two objects due to a temperature difference between them.
work
force acting over a distance
pathway
In rolling to the bottom of the hill shown in Fig. 6.1, ball A will always lose the same amount of potential energy. However, the way that this energy transfer is divided between work and heat depends on the specific conditions—the pathway.
state function
a property that is independent of the pathway
system
that part of the universe on which attention is to be focused
surroundings
everything in the universe surrounds a thermodynamic system
exothermic
refers to a reaction where energy (as heat) flows OUT of the system
endothermic
refers to a reaction where energy (as heat) flows INTO the system
thermodynamics
the study of energy and its interconversions
first law of thermodynamics
the energy of the universe is constant; same as the law of conservation of energy.
internal energy
a property of a system that can be changed by a flow of work, heat, or both; Delta
E = q + w, where delta E is the change in the internal energy of the system, q is heat, and w is work
enthalpy
a property of a system equal to , E + PV where E is the internal energy of the system, P is the pressure of the system, V and is the volume of the system. At constant pressure the change in enthalpy equals the energy flow as heat.
calorimeter
The device used experimentally to determine the heat associated with a chemical reaction is called a calorimeter.
calorimetry
the science of measuring heat flow
heat capacity
the amount of energy required to raise the temperature of an object by one degree Celsius.
molar heat capacity
the energy required to raise the temperature of one mole of a substance by one degree Celsius.
specific heat capacity
the energy required to raise the temperature of one gram of a substance by one degree Celsius.
constant-pressure calorimetry
he measurement of heat using a simple calorimeter such as that shown in Fig. 6.6 is an example of constant-pressure calorimetry, since the pressure (atmospheric pressure) remains constant during the process. Constant-pressure calorimetry is used in determining the changes in enthalpy (heats of reactions) for reactions occurring in solution. Recall that under these conditions, the change in enthalpy equals the heat; that is, Delta H =qp
constant-volume calorimetry
Constant-volume calorimetry experiments can also be performed. For example, when a single-use hot pack is activated, the pack becomes very hot as the calcium chloride dissolves in the water and does so exothermically. This process occurs inside the pack and does not change volume.
Hess’s law
in going from a particular set of reactants to a particular set of products, the enthalpy change is the same whether the reaction takes place in one step or in a series of steps; in summary, enthalpy is a state function.
