Chapter 10: Thermochemistry Flashcards
Thermochemistry
The study of the relationships between chemistry and energy.
energy
Capacity to do work
work
the result of a force acting through a distance
heat
The flow of energy caused by a temperature difference.
kinetic energy
The energy associated with the motion of an object.
thermal energy
The energy associated with the temperature of an object. It is actually a type of kinetic energy because it arises from the motions of atoms or molecules with a substance.
potential energy
The energy associated with the position or composition of an object.
chemical energy
The energy associated with the relative positions of electrons and nuclei in atoms nd molecules. It is also a form of potential energy.
law of conservation of energy
States that energy can be neither created nor destroyed.
system
In thermodynamics, the portion of the universe that is singled out for investigation.
surroundings
In thermodynamics, everything in the universe that exists outside the system under investigation.
Thermodynamics
The general study of energy and its interconversions.
First law of thermodynamics
The law of energy conservation which states that “the total energy of the universe is constant.”
internal energy (E)
The sum of the kinetic and potential energies of all of the particles that compose the system.
state function
A function whose value depends only on the state of the system, not on how the system got to that state. Internal energy is a state function.
Change in internal energy ΔE of a chemical system
ΔE = Eproducts - Ereactants
Energy flow between system and surroundings
ΔEsystem = -ΔEsurroundings
Relationship between internal energy, heat, and work
The change in the internal energy of the system (ΔE) is the sum of the heat transferred (q) and the work done (w).
ΔE = q + w
q (heat)
- +system gains thermal energy
- system loses thermal energy
w(work)
- work done on the system
- work done by the system
ΔE (change in internal energy)
- energy flows into the system
- energy flows out of the system
thermal equilibrium
There is no additional net transfer of heat.
qsystem = - qsurrounding
heat capacity
(C) The quantity of heat required to change its temperature by 1 °C.
C = q/ΔT = J/°C
relationship between heat (q), temperature (T), and heat capacity
q = C x ΔT
specific heat capacity
The measure of the intrinsic capacity of a substance to absorb heat. The amount of heat required to raise the temperature of 1 gram of the substance by 1°C.
Unit is J/g •°C
molar heat capacity
The amount of heat required to raise the temperature of 1 mole of a substance by 1°C. Unit is J/mol•°C
Relationship between Heat (q), Mass (m), Temperature (T), and specific heat capacity of a substance (Cs)
q = m x Cs x ΔT
pressure-volume work
When the force is caused by a volume change against an external pressure.
pressure
The force that pushes against the cylinder divided by the area of the cylinder.
Relationship between work, pressure, and change in volume
w = -PΔV
As the volume of the cylinder increases, work is done on the surroundings by the system, so w should be negative. Upon expanision, V2 is greater than V1 so ΔV is positive. In order for w to be negative for a positive expansion, we need to add a negative sign to our equation.
