ACS Chemistry Thermodynamics

What is the third law of thermodynamics?

The entropy of a perfect crystal is zero.

What is the second law of thermodynamics?

As a whole, the universe always tends towards increasing entropy.

What is the relationship between number of microstates and entropy?

More microstates = higher entropy

What is the relationship between temperature and entropy?

Temperature increases, entropy increases (direct)

What is the relationship between atomic weight and entropy?

Heavier = increased entropy (direct)

What happens to entropy when a substance is dissolved in another?

Entropy increases

What is the relationship between moles of gas and entropy?

When moles of gas increase, entropy increases (direct)

What is the relationship between free energy, enthalpy, and entropy?

deltaG(system)=deltaH(system)-TdeltaS(system)

What does change in G measure?

The extent of the spontaneity of a process, and the useful energy available from it

What is the relationship between work and spontaneous processes?

Spontaneous processes produce work

What is the relationship between work and non-spontaneous processes?

Non-spontaneous processes require work

What does -w mean?

Work is being produced - spontaneous

What does a positive sign for w mean?

Work is required - non-spontaneous

Can a change be spontaneous in both directions?

No

What is an extensive property?

Value depends on the amount of substance

What does ΔG \> 0 mean?

Non-spontaneous process - requires work

What does ΔG < 0 mean?

Spontaneous process - produces work

What does standard free energy of formation mean? ΔGo

The free energy change that occurs when 1 mole of a compound is made from its elements

What is the standard free energy of formation for an element in its standard state? ΔGf

0

What does reversing a reaction do to the standard free energy of formation? ΔG0

Changes its sign

Why are most exothermic reactions spontaneous?

Because the large negative ΔH/large energy release makes the free energy change negative.

What happens when ΔH and ΔS have opposite signs?

The reaction occurs spontaneously at all temperatures or at none.

What happens when enthalpy (ΔH) is negative and entropy (ΔS) is positive?

Spontaneous at all temperatures, negative free energy

What is the likely sign of ΔH and ΔS for a combustion reaction?

Negative ΔH, positive ΔS

What happens when ΔH is positive and ΔS is negative?

Nonspontaneous at all temperatures

What happens when ΔH and ΔS are both positive?

Reaction becomes spontaneous as temperature increases

What happens when ΔH and ΔS are both negative?

Reaction becomes spontaneous as temperature decreases

Why can the maximum work of a system never obtained from a real process?

Because such an irreversible process will always involve some free energy being converted to heat

How do you find where a reaction becomes spontaneous?

Set ΔG equal to zero and solve -- use T=deltaH/deltaS to find the temperature value.

Is a chemical reaction proceeding to equilibrium a spontaneous or non-spontaneous change?

Spontaneous

How to determine reaction direction from ΔG?

ΔG

Which direction does the reaction proceed if ΔG is positive?

To the left / to reactants

Which direction does the reaction proceed if ΔG is negative?

To the right/ to products

How to predict ΔS(system)? (change in entropy of a system)

Positive ΔS(system) means available microstates increases/disorder increases

How to calculate the ΔSo (aka standard entropy change) of the formation of one mole of gas from its elements?

1. Write the balanced chemical equation with the proper coefficients that make the product ONE MOLE.2. Find the value of the one mole of product in Appendix B. This is the deltaS(standard) for the product.3. Find the value of the reactants in Appendix B for deltaS(standard) and multiply them by the coefficients you got in step 1.4. Use total = products-reactants for your final value.

How to calculate ΔG (free energy) using enthalpy ΔH and entropy ΔS values?

ΔG=ΔH-TΔS

What is the equation that relates ΔG to K?

ΔG=-RT ln K

What is the Boltzmann constant?

ln(\# of microstates)

What does a big W mean?

More microstates

What does more microstates mean?

Big ΔS - more entropy

What does fewer microstates mean?

Smaller ΔS - less entropy

What happens to entropy when volume is increased?

Microstates increase, entropy increases

What is the relationship between ΔS of a system, q, and T?

ΔS(system)=qrev/T

What happens to entropy ΔS when temperature increases?

It increases

What is the relationship between mass and entropy ΔS?

As mass increases, entropy increases

What is the relationship between molecular complexity and entropy ΔS?

As molecular complexity increases, entropy increases

What is the relationship between ΔG and Q?

ΔG=RTlnQ

What happens to K as ΔG becomes more positive?

It gets smaller

What happens to K as ΔG becomes more negative?

It gets bigger

What direction does a reaction proceed if ln Q/K is positive?

Reaction proceeds to the left/reactants

What direction does a reaction proceed if ln Q/K is negative?

Reaction proceeds to the right/products

Extensive Property

property which is directly proportional to the size of the system (i.e.. V, m, E )

Intensive Property

property which does not depend on the size of the system (i.e. P, T, density, molar volume)

van der Waals constants

a reflects how strong the molecules attract each other (IM forces); b reflects the size of the molecule\--- van der Waals equation extends beyond the ideal gas law to take into account attractive and repulsive forces

Isotherm

plot of P as a function of molar volume at constant temperature

Law of Corresponding States

Law which states "all gases have the same properties of they are compared at corresponding conditions"

Boyle Temperature

temperature at which repulsive and attractive interactions cancel and the gas appears to behave ideally

Heat (q)

the manner of energy transfer that results from temperature difference between system and surroundings ("unorganized motion")

Work (w)

the transfer of energy between system and surroundings as a result of existence of unbalanced forces between the two ("organized motion")

State Function

property that depends on the state of the system, and not upon the history of the system (i.e. energy, entropy)

Reversible Process

when pressure the pressure exerted on the system and the pressure of the system differ only infinitesimally so slight changes are able to be made

Path Function

property that depends on the path taken to reach the state of the system

Adiabatic Process

process which no energy as heat is transferred (dq = 0 ; therefore, dU=dw )

Enthalpy (H)

total heat content of a system; it is equivalent to the internal energy plus the products of pressure and volume

Heat of Combustion

the heat involved in a combustion reaction--chemical reactions that absorb heat ( dH \> 0) are called endothermic--chemical reactions that release heat (dH

Entropy (S)

unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system\---dS=0 for cyclic processes or reversible processes in isolated system\---dS \> 0 for spontaneous processes in isolated systems

Helmoltz Energy (A)

= U - TS\---will decrease during any spontaneous process that occur at constant T and V and will achieve its minimum value at equilibrium

Gibbs Energy (G)

= H - TS = A + PV\---will decrease as a result of any spontaneous process until the system reaches equilibrium

Fugacity

thermodynamic property which described the deviations of ideality; the ratio f/p is the coefficient

Gibbs Phase Rule

F = C - P + 2\---Phase (P): numer of phases ( P=1 is for within a region, P=2 is for on the coexistence curve, P=3 is for at the critical point)\---Component (C): chemically independent variable describing how many components are in the system\---Degrees of Freedom (F): number of intensive variables we can change yet still be in the same phase

Azeotrope

a mixture for which there is no change in composition upon boiling (not possible to achieve separation)

Colligative Property

property which depends only on the number of solute particles present, not on their identity (i.e. vapor pressure, boiling point, freezing point, osmotic pressure)

Reaction Quotient (Q) vs. Equilibrium Constant (K)

\--- at equilibrium dG=0 ; Qp=Kp\--- If Qp < P: dG

Colloids

Contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension

Bose-Einstein Condensate

Fifth state of matter that exists at extremely low temperatures and atoms behave as a single particle

Pressure

Result of force distributed over an area

Charles's Law

The volume of a gas is directly proportional to its temperature in kelvins if the pressure and the \# of particles of the gas are constant

Boyle's Law

The volume of a gas is inversely proportional to its pressure if the temperature and the \# of particles are constant

Endothermic

The system absorbs energy from its surroundings

Heat of Fushion

The energy a substance must absorb in order to change from a solid to liquid

Exothermic

The system releases energy to its surroundings

Deposition

When a gas changes directly to a solid

Sublimation

When a solid changes directly to a gas

Alkaline Earth Metals

The elements in group 2A; differences shown by reactivity to water

Halogens

The elements in group 7A; highly reactive nonmetals

Noble Gases

The elements in group 8A; colorless odorless and extremely unreactive

Anion

An ion with a negative charge

Cation

An ion with a positive charge

Polar Covalent Bond

A covalent bond in which electrons are not shared equally

2. An equation of state interrelates

pressure, volume, temperature, and amount of substance: p = f(T,V,n).

6. A diathermic boundary is a boundary that

permits the passage of energy as heat.

7. An adiabatic boundary is a boundary that

prevents the passage of energy as heat.

7. Thermal equilibrium is a condition in which

no change of state occurs when two objects A and B are in contact through a diathermic boundary.

8. The Zeroth Law of thermodynamics states that

if A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C is also in thermal equilibrium with A.

9. The Celsius and thermodynamic temperature scales are related by

T/K = θ/°C + 273.15.

10. A perfect gas obeys the perfect gas equation

pV = nRT, exactly under all conditions.

11. Dalton's law states that the

pressure exerted by a mixture of gases is the sum of the partial pressures of the gases.

12. The partial pressure of any gas is defined as

p_J = x_J p, where x_J = n_J/n is its mole fraction in a mixture and p is the total pressure.

13. In real gases, molecular interactions affect the equation of state; the true equation of state is expressed in terms of virial coefficients

B, C, . . . : pV_m = RT(1 + B/V_m + C/V^2_m + · · · ).

14. The vapour pressure is the

pressure of a vapour in equilibrium with its condensed phase.