CHM Exam 2 Flashcards (Chapter 9 and Chapter 10)
Energy
the capacity to do work or produce heat
First Law of Thermodynamics
energy is conserved and can be converted from one form to another
Energy is/isn’t a statement function
is
the internal energy for a system is the
sum of its potential and kinetic energy
the internal energy of a system can be changed by
work and heat
Internal energy formula
△E = q + w
work
force applied over a distance
Work is/isn’t a state function
isn’t
Heat
energy flow due to temperature difference
exothermic
energy as heat flows out of a system
endothermic
energy as heat flows into a system
Heat is/isn’t a state function
isn’t
Enthalpy forumla
H = E + PV
Formula for heat
q = mC△T
Enthalpy is/isn’t a state function
is
Hess’s Law
the change in enthalpy in going from a given set of reactants to a given set of products is the same whether the process takes place in one step or a series of steps
△H of reaction formula
△H(reaction) = sum of △H of products - sum of △H reactants
Heating an ideal gas at constant volume
- no PV work done
- all energy used to increase the translational energies of the gas molecules
- bomb calorimeter
Heating an ideal gas at constant pressure
- PV work done
- energy is used to increase the translational energies of gas molecules and do work
- coffee cup calorimeter
State function
refers to a property of a system that depends only on its present state
energy gained by the surroundings must be…
equal to the energy lost by the surroundings
work done by a gas
expansion
work done to a gas
compression
1 Latm = x J
101.325 J
small font = flow = ?
work (w) and heat (q)
capital font = state function = ?
Energy (E) and Enthalpy (H)
q of system = ?
- q of surroundings
An open system can exchange ____ with its surroundings
energy and matter
A closed system can exchange ____ with its surroundings
only energy
A isolated system can exchange ____ with its surroundings
neither energy or matter
Water has a high heat capacity because
of its hydrogen bonds
exothermic = ?
endothermic = ?
exothermic = negative
endothermic = positive
formula for pressure
P = (w)/(-△V)
What are the 5 applications of thermochemistry?
- phase changes
- dissolution of solids into liquids
- enthalpy of chemical reactions
- redox chemistry
- combustion of hydrocarbons
Energy in the universe is constant
1st law of thermodynamics
Second Law of Thermodynamics
states that for any spontaneous process there is always an increase with the entropy of the universe
Entropy
the thermodynamic function that describes the number of arrangements (positions and/or energy levels) available to a system existing in a given state
Nature spontaneously proceeds toward states that have the _____
highest probability of occurring
Using entropy, thermodynamics can ____
predict the direction in which a process will occur spontaneously
Entropy of universe formula
△S (universe) = △S (system) + △S (surroundings)
For a spontaneous process, △S (universe) must be
positive
△S (system) is dominated by
positional entropy
For a chemical reaction, △S (system) is dominated by changes in
the number of gas molecules
△S (surroundings) is determined by heat (formula?)
△S (surroundings) = (-△H)/(T)
△S (surroundings) is positive for exothermic processes because
△H is negative
Because △S (surroundings) depends inversely on T, exothermicity becomes more of an important driving force at
low temperature
Thermodynamics can/can’t predict the rate at which a system will spontaneously change
can’t
Third Law of Thermodynamics
states entropy of a perfect crystal at 0K is zero
Free energy is/isn’t a state function
is
Free Energy
a process ocurring at constant temperature and pressure is spontaneous in the direction in which its free energy decreases
Standard state is at
25 C, and 1 atm
△G = 0
K = 1
△G < 0
K > 1, G products < G reactants
△G > 0
K < 1, G products > G reactants
positional microstates _____ as you go from a solid to a liquid to a gas
increase
Change in entropy formula
△S = nCln[T(final)/T(initial)]
Standard free energy change formula
△G = △H - T△S
the number of micro states ____ with the temperature _____
increases, increases
△G depends on _____ and _____
concentration and temperature
What are the three ways to find △G of a reaction?
- △G = △H - T△S
- △G = sum of △G(products) - sum of △G(reactants)
- △G = -RTlnK
The thermodynamic quantity that expresses the degree of disorder in a system is
entropy
Which one is always positive when a spontaneous process occurs?
△S univ
What can be said about a chemical system that has reached a minimum in free energy?
The system has achieved equilibrium
A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if △H is _____ and △S is ______
+, +
For a reaction to be spontaneous under standard conditions at all temperatures, the signs of △H and △S must be _____ and ____ respectively
-, +T
The greater the dispersal of matter and/or energy in a system, the _____ the entropy
larger
The entropy of a substance always _____ as it changes from solid to liquid to gas
increases
When a pure solid or liquid dissolves in a solvent, the entropy of the substance _______
increases
When a gas molecule escapes from a solvent, the entropy _____
increases
Entropy generally increases with ______ molecular complexity since there are more moving electrons
increasing
Reactions increasing the number of moles of particles often ______ entropy
increase
