Thermochemistry

What is an exothermic process?

A process where heat leaves the system and goes into the surroundings.

What is an endothermic process?

A process where heat leaves the surroundings and enters the system.

If an exothermic process is occurring inside a container, the container should feel…

hot/warm

If an exothermic process is occurring inside a container, the container should feel…

cold/cool

Temperature is a measurement of…

the average amount of kinetic energy a system contains (how fast those particles are moving).

True or False: Temperature is a measurement of the system.

False. Temperature is a measurement of the surroundings.

What unit is specific heat capacity given in?

Per gram

What unit is molar heat capacity given in?

Per mole

What equation do we use to find heat (q)?

q = nC(D)T

What equation do we use to find a change in internal energy, (D)E, given heat capacity at constant volume?

(D)E = nCv(D)T

What equation do we use to find a change in enthalpy, (D)H (and qp), in isobaric conditions?

(D)H = qp = nCp(D)T

What is the “heat” required to change the temperature of 1 mole of gas by 1K in isochoric conditions?

Cv = 3/2R, where R = 8.3145 J/mol k

What is the “heat” required to increase the temperature of 1 mole of gas by 1K in isobaric conditions?

Cp = 5/2R, where Cv + R = 5/2R and R = 8.3145 J/mol K

What is the relationship between qwater and qmetal in a calorimetry experiment?

qwater = -qmetal, where a piece of metal is dropped into water.

When is the internal energy, (D)E, greater than 0?

Heat enters the system (endothermic) and work is done on the system (W>0).

When is the internal energy, (D)E, less than 0?

Heat leaves the system (exothermic) and work is done by the system (W<0).

What equation do we use to find (D)E?

(D)E = q + w, where q is heat and w is work.

What is an equation used to find (D)H for a gas?

(D)H = (D)E + (D)PV

What is an equation used to find work at constant pressure?

w = -P(D)V

What is the relationship between (D)H and q at constant pressure?

(D)H = qp

What is the relationship between (D)E and q at constant volume?

(D)E = qv

Explain Hess’s Law

According to Hess’s Law, the (D)H of a reaction is not dependent on the different steps it takes to get from one form to another. It is simply the total (sum) enthalpy required to go from point A to point B.

What are state functions?

Indicated by capital letters, state functions is pathway-independent.

What are not state functions?

Indicated by lowercase letters, non state functions are pathway-dependent.

What state functions must we know for thermodynamics?

(D)H, (D)S, (D)G, (D)E

What non state functions must we know for thermodynamics?

q, w

What does isothermal mean?

Constant temperature

What is (D)E in isothermal conditions?

(D)E = 0

What is q in isothermal conditions?

q = -w

What is w in isothermal conditions?

w = -q

How do you find qrev (and - wrev) in isothermal conditions & reversible?

qrev = -wrev = nRTln(V2/V1)

What does isobaric mean?

Constant pressure

What is (D)H in isobaric conditions?

(D)H = qp

What is (D)E in isobaric conditions?

(D)E = (D)H + w = qp + w

What does isochoric mean?

Constant volume

What is (D)E in isochoric conditions?

(D)E = qv

What is w in isochoric conditions?

w = 0

How do you find (D)E (and qv) in isochoric conditions?

(D)E = qv = nCv(D)T

When going from solid to liquid, what sign is entropy (D)S?

(D)S > 0

When going from liquid to solid, what sign is entropy (D)S?

(D)S < 0

When going from liquid to gas, what sign is entropy (D)S?

(D)S > 0

When doing from gas to liquid, what sign is entropy (D)S?

(D)S < 0.

Explain microstates

More microstates = more arrangements of the particles = increase in entropy

How to solve for entropy S in terms of microstates?

S = Kbln(omega), where omega is number of microstates.

How to solve for change in entropy (D)S in isothermal and isobaric conditions? Otherwise known as phase changes.

(D)S = qrev/T = (D)H/T

How to find change in entropy (D)S in isothermal reversible conditions?

(D)S = nRln (V2/V1)

How to find change in entropy (D)S in isobaric conditions?

(D)S = nCpln(T2/T1), where Cp = 5/2R

How to find change in entropy (D)S in isochoric conditions?

(D)S = nCvln(T2/T1), where Cv = 3/2R

What is the second law of thermodynamics? Why?

(D)Suniv is always increasing or greater than 0 because all real processes are spontaneous.

What is (D)S for spontaneous reactions?

(D)Suniv > 0

What is (D)S for spontaneous reactions?

(D)Suniv > 0

What is (D)S at equilibrium?

(D)Suniv = 0

How do you solve for (D)Suniv ?

(D)Suniv = (D)Ssys + (D)Ssurr

How do you solve for (D)Ssys in isothermal conditions?

(D)Ssys = -qrev/Tsys

How do you solve for (D)Ssurr in isothermal conditions?

(D)Ssurr = qrev/Tsurr

What is the third law of thermodynamics?

The entropy of a pure, perfect crystalline substance at absolute zero (0K) is 0.

What are standard entropies S^o ?

The entropy of one mole of substance under standard conditions (pressure of 1 bar/1atm and temp of 298.15K).

How do you find the change in standard entropy (D)S^o ?

(D)Sstandard = ZSstandard(products) - ZSstandard(reactants)

What is Gibb’s free energy?

The total available energy that can be used to drive a reaction (thermodynamic potential).

How do you solve for change in gibb’s free energy (D)G?

(D)G = (D)H - T(D)S

What is the relationship between (D)G and work?

(D)G = wmax.

If both (D)H and (D)S are positive, when is the reaction spontaneous?

At higher temperatures

If both (D)H and (D)S are negative, when is the reaction spontaneous?

At lower temperatures

When is the reaction not spontaneous at all temperatures?

(D)H is positive and (D)S is negative.

When is the reaction spontaneous at all temperatures?

(D)H is negative and (D)S is positive.

How do you solve for (D)G in terms of an equillibrium process?

(D)G = (D)Gstandard + RTln(Q)

How do you solve for (D)Gstandard at equilibrium?

(D)Gstandard = - RTln(K)

How do you solve for K in terms of (D)Gstandard?

K = e^-[(D)G/RT]

What is K and (D)G at equillbrium?

K = 1 and (D)G = 0

What is K and (D)G when the reaction is forward favored?

K > 1 and (D)G < 0

What is the K and (D)G when the reaction is reverse favored?

K < 1 and (D)G > 0

What is work?

Force applied over a distance; usually in expansion and compression problems.

What sign is work when work is done on the gas? (compression)

w > 0

What sign is work when work is done by the system? (expansion)

W < 0

What is heat?

Thermal transfer of energy; not the same as temperature because heat is dynamic.

What sign is heat when absorbed by the system?

q > 0

What sign is heat when released by the system?

q < 0

For monoatomic ideal gases, what is Cv and Cp?

Cv = 3/2R and Cp = 5/2R

For polyatomic ideal gases, what is Cv and Cp?

Cv > 3/2R and Cp >5/2R

Where does heat transfer occur in a calorimeter?

System to water. Water is considered the “surroundings” since calorimeters are perfectly insulated.

What does bomb calorimeter imply?

Constant volume

What does coffee cup calorimeter imply?

Constant pressure

What is the first law of thermodynamics?

Energy cannot be created or destroyed, only transferred through work or heat.

What does the first law of thermodynamics allow us to assume?

qsys = - qsurr (same for w)

What type of calorimeter measures change in internal energy (D)E ?

Bomb calorimeter

What type of calorimeter measures change in enthalpy (D)H?

Coffee cup calorimeter

How do you solve for the ratio of microstates?

(D)S = Kbln(omega 2/omega 1), where omega is the number of microstates.

True or False: Entropy is conserved.

False. We cannot assume (D)Ssys = (D)Ssurr

What does(D)Suniv determine?

Spontaneity

What does (D)G determine?

spontaneity of system

What does (D)Gstandard determine?

equilibrium position

What does a vant’hoff plot do?

It relates ln(k) to 1/T in the form of y = mx+b

What is the slope of a vant’hoff plot?

-(D)H/R

What is the y-intercept of a vant’hoff plot?

(D)S/R

What is protein design?

Identifying new amino acid sequences that can fold into a structural framework of choice.

What is protein prediction?

Using a known amino acid sequence to predict its structure.