Quiz 2 Flashcards
How do you calculate Cp for an ideal gas?
Cp = Cv +nR
Why is Cp larger than Cv?
not only do we increase the temperature when we add heat, but we also do pressure volume work against atmospheric pressure
What is the general definition of Cv? Cp?
Describe the energy of an ideal gas.
The energy of an ideal gas is purely kinetic, for an ideal gas the internal energy only depends on temperature not volume or pressure
What is the enthalpy state function?
H = U + PV
What is the relationship between enthalpy and heat at constant pressure? What conditions does this equation depend on?
dH = dQp
- mechanical equilibrium between system and surroundings (reversible process)
- no additional work other than pv work
What is the si unit for volume and how does that relate to L?
m3
1 L = 0.001m3
What is described by the two work equations for isothermal expansion?
the work the system does on the surroundings
Equation for work the system performs on the surroundings when heating a solid liquid or gas reversibly under constant pressure
w= -p(v2 - v1)
- pV work upon reversible heating at constant external pressure
Internal energy equation for heating a liquid with phase transition?
w= -p(v2 - v1)
but also:
dU = Cvm(T2-T1)
What does isobaric mean?
same pressure
What does isochoric mean?
same volume
How do you calculate dH during a phase change?
What does thermochemistry study?
the heat transferred in chemical reactions
Why are standard states important?
- so we can measure relative changes in dH
- like sea level
What is the standard state?
- the most stable state of a material at 1 bar and a specified temperature
What are the standard states of gas, solid, liquid, and solution?
Gas - pure gas at 1 bar
Solid - crystalline solid at 1 bar
Liquid - states of the liquid at 1 bar
Solution - substance in a solution with conc 1M and at pressure of 1 bar
What is the standard enthalpy of formation?
- the reaction enthalpy for the formation of the compound from its elements in their reference states
What is the reference state of an element?
its most stable form under standard conditions (1 bar, pure element, specified T)
What does the definition of standard enthalpy of formation imply?
makes the standard enthalpies of formation of elements in their reference states zero at all temperatures (enthalpies of “null” reactions)
What is Hess’s Law?
If two or more chemical equations are added to give another chemical equation the corresponding enthalpies are added
What is a spontaneous process?
- Occurs without ongoing outside intervention
- although reverse processes are also possible, they require work to be done
- all processes that require work are non-spontaneous
What is entropy? (words)
a measure of energy dispersal
Describe entropy - conservation and function
- entropy is a state function - need to find the amount of reversibly exchanged heat qrev as the system is going from the initial to the final state, even when the process is irreversible
- unlike energy, entropy is not conserved; the entropy of an isolated system increases in the course of a spontaneous process
What are two classes of processes?
spontaneous and nonspontaneous
Why does a ball not bounce as high on the next bounce?
The energy that is concentrated in the ball is dispersed in the surroundings.
Hallmark of spontaneous change
direction of change that leads to the dispersal of the total energy in the universe
What is entropy intimately related to?
- excitation of vibrational modes are related to heat transfer - we can easily accept that entropy is intimately related to heat transfer
What is the basic entropy equation?
When are these equations true?
H = U +pV
dH = dU +pdV
- first definition is true under all conditions (general definition of enthalpy)
- second definition is true only under constant pressure
What is the equation for enthalpy change upon reversible heating under constant pressure (no phase change)?
dH = nCpm(T2-T1)
How do you use enthalpy state transition equations when adding?
- if it is in the reactants (make -)
- if it is in the products add as is
Entropy is a ______ function
state
- change applies to reversible and irreversible processes
What is the message of the clausius inequality?
a process can occur spontaneously if the total entropy of the universe increases in the course of the process
Describe the Clausius inequality in the case of reversible and irreversible processes.
How do you calculate enthalpy at a temperature other than 25?
What is the Clausius inequality?
Explain the basic interaction between energy and probability and give the equation.