Home > Preview
The flashcards below were created by user
on FreezingBlue Flashcards.
the study of the transformations of energy from one form into another
Open system - can exchange both matter and energy with its surroundings (car engines, human body)
Closed – has a fixed amount of matter, but can exchange energy with its surroundings (cold pack)
Isolated – has no contact with surroundings (hot liquid in vacuum flask)
We can classify any system according to its interactions with its ________. A(n) ______ system can exchange matter and energy with its _______. While ______ systems can exchange neither matter nor energy.
When a system experiences a change in one or more of its properties, it undergoes one of 3 processes. Name them
- Isothermal processes: occur when the system’s temperature is constant
- Adiabatic processes: occur when no heat is exchanged between the system and the environment; thus, the heat content of the system is constant throughout the process
- Isobaric processes: occur when the pressure of the system is constant
- Internal energy:
- Work: The process of achieving motion against a force
- Internal energy: total energy of a system
Work is the transfer of _____ to a system by a process that is equivalent to raising or lowering a weight. For work done on a system, w is ______; for work done by a system, w is ______. The internal energy of a system may be changed by doing work: in the absence of other changed, ΔU=__
With other changes present in addition to work, ΔU=
heat added to the system (q)+work (w)
w=force (f)xdistance (d)
Standard conditions vs Standard temperature and pressure
- Standard conditions: 298K and 1atm
- Standard temp and press (STP): 273K and 1atm
What do these symbols stand for
- ΔH°: Standard enthalpy
- ΔS°: Standard entropy
- ΔG°: Standard free energy
a function defined for a system relating several state variables or state quantities that depends only on the current equilibrium state of the system. State functions do not depend on the path by which the system arrived at its present state.
List 8 state functions
- Temperature (T)
- Pressure (P)
- Volume (V)
- Density (ρ)
- Internal energy (E or U)
- Enthalpy (H)
- Entropy (S)
- Gibbs free energy (G)
Heat vs Temperature (NOT THE SAME)
- Heat: is the transfer of energy from one substance to another as a result of their difference in temperature
- Temperature: is a measure of the average kinetic energy of the particles in a system
The unit of heat is the same as the unit of energy, it is the ______ or the _____.
Joule (J) or the calorie (cal)
___ cal = _____ J
1 cal = 4.184 J
Heat equation most commonly used in calorimetry problems
c or Cs: the amount of energy required to raise the temperature of one gram or kilogram of a substance by one degree Celsius or one unit Kelvin
Cs or specific heat is also called ____ ____ ____
specific heat capacity
For water c = ____
Molar heat capacity (equation)
Cm or C= qΔT
Transfers of energy as heat are measured with a calorimeter. Define calorimeter
a device in which heat transfer is monitored by recording the change in temp. that it produces
Heat equation with respect to the calorimeter constant
- Ccal= heat capacity of calorimeter (calorimeter constant)
The state function that allows us to keep track of energy changes at constant pressure
Positive value of enthalpy=
- negative value of enthalpy=
Standard enthalpy of formation
ΔH°f, is the standard reaction enthalpy per mole of formula units for the formation of a substance from its elements in their most stable form
State the exception to the enthalpy rule and why?
- White phosphorus is used because it is much easier to obtain pure than the other more stable allotropes
standard enthalpy of a reaction
ΔH°rxn, is the hypothetical enthalpy change that would occur if the reaction were carried out under standard conditions
Hess' Law states that enthalpy changes are ______
Hess' Law can also be expressed in terms of ____ ______, also called _____ ______ _____, which is the average energy that is required to break a particular type of ____ between atoms in the gas phase (endothermic)
- bond enthalpies
- bond dissociation energies
Standard heat of combustion
ΔH°comb, enthalpy of physical changes
ΔH°L, For a solid, the difference in molar enthalpy between the solid and a gas of widely separated ions
If a system is cooler than its surroundings, what happens? What is this phenomena called?
Energy flows from the surroundings to the system. This is called the transfer of the energy of thermal motion
When the internal energy of the system is changed b transferring energy as heat (and no other processes, including expansion or contraction, take place), what is the value of your internal energy?
If energy enters the system as heat, the internal energy of the system ______ and q is ______; if energy leaves the system as heat, the internal energy of the system ______ and q is _____.
If the walls are thermally insulating, heat ____ be transferred across them, even if there is a temperature ______ across them. A good example are the walls of a vacuum flask, because the ______ between them _____ allow energy to be conducted from one wall to another by molecules and their_____ surfaces cuts down the transfer of energy by ______.
- silvered surfaces
The technical term for thermally insulating wall is ______ _____.
adiabatic wall (greek for not passing through)
A system with adiabatic walls is not necessarily an isolated system, explain:
energy may be transferred to or from a system and adiabatic system as work (for ex if it is a closed adiabatic system where ΔU = w)
Diathermic walls permit the transfer of energy as _____ as long as the system does not lose energy as ______.
An influx of energy through the walls of a diathermic container typically raises the _____ of the system. How does this help with internal energy?
- Monitoring the change in temp, allows us to monitor heat transferred which is a direct indicator of internal energy (as long the system doesn't lose energy as work)
A large heat capacity means that a ______ supply of heat produces a ______ rise in temperature while a small heat cap. means that a _____ transfer of energy will produce a ______ rise in temp.
- Cm =
- Cs = C/m
- Cm = C/n
- ∴q= mCs ΔT
- ∴q= nCm ΔT
Transfers of energy as heat are measured with a ______, a device in which _____ transfer is monitored by recording the change ______ produced by the process taking place within it.
Heat lost by a ______ is gained by the calorimeter; that is -q =?
How do we measure heat gained by the calorimeter? (2)
What is Ccal? (2)
qcal = Ccal ΔT or -q= Ccal ΔT
the heat capacity of the calorimeter or the calorimeter constant
2 steps to finding the heat capacity of a calorimeter and what is the process called?
- a) supply a known amount of heat
- b) not the resulting rise in temp
- this is called calibrating the calorimeter