Exam 2 Flashcards
Thermochemistry
the study of the changes in energy that accompany chemical reactions
Thermodynamics
study of the relationship between heat, work, and energy
chemical energy
One form of PE, dependent upon the way the atoms are bonded together
Intramolecular forces
chemical bonds between atoms
intermolecular forces
interactions holding molecules/atoms close
Breaking chemical bonds
energy is absorbed (energy is required)
Forming chemical bonds
energy is released (energy goes out)
internal energy
the sum of all kinetic and potential energy of an object. Units are J or calories
What is it called going from solid to liquid
fusion
what is it called going from liquid to gas
vaporization
what is it called going from solid to gas
sublimation
Triple point on phase diagram
The triple point on a phase diagram is a unique point where three phases of a substance (solid, liquid, and gas) coexist in thermodynamic equilibrium. At this specific temperature and pressure, the substance can simultaneously exist in all three states.
what is the critical point in a phase diagram
The critical point on a phase diagram is a specific temperature and pressure at which the liquid and gas phases of a substance become indistinguishable.
heat is the transfer of
energy between systems and surroundings
high energy correlates to
“hot”
Is heat a property of matter?
No, heat is a transfer (accomplished by collisions)
Endothermic
Heat is transferred to the system (q=+)
Exothermic
heat leaves the system (q=-)
As heat is added to the phase changes
it is an endothermic process (going from solid to liquid to gas)
As heat is taken away from the phase changes
it is an exothermic process (gas to liquid to solid)
Which phase change has the lowest PE
Solid
Which phase has the highest PE
gas
Define “work”
the amount of energy expended (or produced) by a force acting over a distance
What does work do when volume decreases
work increases; work is done on the system by the surroundings
what does work do when volume increases
work decreases; work is done by the system on the surrounding
first law of thermodynamics
states that energy is neither created nor destroyed
Enthalpy
is the sum of the internal energy (E) and the work done to create the space
state function
processes that are independent of the pathway (the middle), only depends on the initial and final values. The pathway in between can be real or hypothetical.
During phase changes on heat diagrams:
PE is increased, KE stays the same, temp stays the same
Between phase changes on heat diagrams:
PE stays the same and KE and Temp increase
heat capacity (Cp)
the energy required to raise the temperature of a substance by 1 degree C (at a constant pressure)
Specific heat (cs)
is measured per gram of a substance
molar heat capacity (cp)
is measured per mole of substance
what does the heat capacity or specific heat relate to?
the temperature change of a substance to the amount of heat absorbed or lost
Calorimetry
an analytical technique in which changes in the temperature of a device with a known heat capacity are used to determine the energy released or absorbed by a process occurring in the calorimeter
Hess’s Law
states that the enthalpy of reaction for a process that is the sum of two or more reactions is equal to the sum of enthalpy of reaction values of the constituent reactions
Rules with thermodynamic equations
states make a difference, enthalpy changes with quantity, sign of enthalpy reverses with equation
Standard conditions are…
1 atm and & 25 degrees Celsius
Phase changes in standard states
s and l must be pure substance, g must behave like an ideal g, aq must be 1.0M
At standard conditions enthalpies of formation for elements must
be in their normal phases and most stable form (most stable allotrope)
standard enthalpy of formation
is the change in enthalpy of one mole of a compound formed from its elements (in standard states)
Types of Particle motion
translational, rotational, vibrational
As temperature increases the proportion of higher energy particles… and the distribution of speeds…
increases, spreads out
Lighter molecules must have … to have the same kinetic energy compared to heavier molecules
higher
Spontaneous process
a process that occurs continuously without outside intervention
Nonspontaneous process
a process that requires outside intervention
Second law of thermodynamics
total entropy of the universe increases for spontaneous processes
third law of thermodynamics
at zero K entropy is zero of a perfect crystal
Entropy, S
a measure of the number of accessible energy states or levels to put energy; measure of randomness
System entropy increases if
there is a temp increase, a phase change, mixing of substances, volume increase, dissolution, chemical reaction
Dalton’s Law
Total pressure is the sum of partial pressures of each of the gases in the mixture
Mole fractions
the ratio of the number of moles of a particular component in the mixture to the total number of moles in the mixture
Partial pressures
The partial pressure that a gas in a mixture exerts is proportional to its mole fraction
Real gases
have IM attraction, particles do have size, deviates from ideality at “high” pressure and “low” temperature
Diffusion
Diffusion of gases is defined as the spread of one substance through another
Effusion
diffusion of gas through a small hole
Equation for heat diagram during phase change
q=nrxn(deltaH)
Equation for heat diagram between phase changes
q=mc(delta T)
Free energy
a measure of the maximum amount of work a thermodynamic system can perform
Gibb’s free energy
the maximum amount of energy released (or required) by a process occurring at constant P and T that is available to do work
what is called when a gas goes to a solid
deposition
what is called when a solid goes to a gas?
sublimation
Determine whether a substance’s solid or liquid phase has a higher density based on the phase
diagram.
look at slope (if negative liquid is denser, if positive solid denser), the densest phase exists at the highest pressure and lowest temperature
System v surroundings
The system is what is being focused on while surroundings are everything else
why are state functions useful?
creates path independence, simplifies calculations, predicting spontaneous
Entropy is a measure of
how dispersed the energy in a system is at a specific temperature.
The greater the number of particles produced upon dissolving the solute
the greater the entropy
Given temperature and heat of vaporization how can you find the molar entropy of vaporization?
rearrange gibbs equation to heat/T
what is delta S at a phase change?
-heat of phase change/T
Combustion reactions are extremely exothermic and
very spontaneous
Mole fraction
xi=ni/ntotal
partial pressure equation
pi=xi(ptotal)
finding density of a gas
grams/Liters
what is the equation for delta E
q + w
