MIDTERM 1

First Law of thermodynamics

Energy cannot be created nor destroyed, only transformed

ΔE = q + w

Second law of thermodynamics

entropy must be increasing over time to be spontaneous

(ΔS_universe > 0 → spontaneous)

Third law of thermodynamics

The entropy of a perfectly ordered crystalline solid approaches zero as its temperature approaches absolute zero

exothermic signs

ΔH = - (favorable)

q = -

endothermic signs

ΔH = +

q = +

if something contracts…

w = +

surroundings do work on system

if something expands…

w = -

system is doing work

↑T

↑P, ↑V

KMT Assumptions

1. Volume of gas particles = 0

2. All collisions are perfectly elastic

3. No IMFs (bc huge distance between particles)

4. Motion is translational & proportional to temperature

If T is constant, how are u_rms & KE affected?

• u_rms would only be affected by M_W = heavier atom → slower speed

• KE remains the same for all atoms

Boltzmann Distribution trends

• As T ↑, the graph spreads out right

• As M_W ↑, the graph becomes skinner to the left

effusion

• going through a pinhole

• Lower M_W = faster rate of effusion

• subtract by 1 to find the percentage *

Path function

DEPENDS on the path taken from initial to final state (ex. heat, work)

State funtion

INDEPENDENT of the path taken (ex. internal energy)

C_V (constant volume)

• 3/2R (for ideal gases)

• ΔE = q_V

• More complex molecules (more bonds) = higher C_V

• w = 0

Why is C_P > C_V?

bc C_P includes pressure-volume work

When is thermal equilibrium reached?

when heat transfer stops

Which state of matter has the highest C_V and why?

Liquids bc they have all motion & strong IMFs

• ideal gases - only translate

• real gases = all motion & little IMFs

• solids - vibrate & strong IMFs

How to find q_rxn from q_cal

q_rxn = -q_cal

C_P (constant pressure)

• 5/2R (for ideal gases)

• ΔE = q_p + w

• q_p = ΔE + PΔV

  • where q_p is a state function

• q_p = ΔH

• w = -RTΔn

ΔH and ΔE are about the same when…

no gases are involved in the reaction

ΔV, ΔE, & ΔH when heating or producing a gas

• ΔV = +

• ΔH > ΔE

  • energy lost to work

ΔV, ΔE, & ΔH when cooling or losing gas in a reaction

• ΔV = -

• ΔH < ΔE

  • work done on system adds energy to system

How does stability/bonds relate to thermo?

• more stable products = more exothermic

• more sigma bonds in products → probably exothermic

bonds vs endo/exo

• breaking bonds → endothermic

• making bonds → exothermic

• with BDE, it’s [bonds broken (reactants) - bonds formed (products)]

How to find temperature when given ΔH and ΔS

Born-Haber Cycle Steps

1. Sublimation(s → g)

2. BDE (break the bond)

3. Ionization (remove electron from cation)

4. Electron affinity (add electron to anion)

5. Lattice Energy

Add them all up to find the ΔH_f

So Bob Is Evil Liar

isothermal

Constant T

favorable signs

ΔH = -

ΔS = +

spontaneous signs

ΔS_universe = +

ΔG = -

What occurs at a phase change?

• ΔT = 0

• Both phases coexist

• All heat is used to break IMFs

ΔS_universe signs

ΔS_universe = 0 → reversible

ΔS_universe > 0 → NOT reversible

ΔS_universe < 0 → can NOT occur

At slope of phase transition

use the equations that have change in temp (ex. ΔH = nC_pΔT)

At constant of phase transition

use the transition values (ex. nΔH_trans)

enthalpy of fusion

s → l

how to compare the entropy of molecules

more bonds & more mass = more entropy

exergonic

ΔG = -

reaction wants to happen (favorable)

endergonic

ΔG = +

the reaction is NOT favorable BUT can still occur (if coupled w/ an exergonic reaction)

How to find Temp when not given

use PV = nRT → T = PV/nR

Label where vaporization, freezing, sublimation, melting, condensation, and deposition occur on the above diagram. Label the triple point and the point where a supercritical fluid is formed in the above diagram.

triple point

all three phases of matter (solid, liquid, and gas) coexist simultaneously

supercritical point

distinct boundary between its liquid and gas phases completely disappears, merging into a single continuous state

How to find S, G, or H from formation energies

products - reactants

How to H from BDE

bonds broken (reactants) - bonds formed (products)

state or path function: ΔH, ΔG, ΔS, ΔE

ΔH - state

ΔG - state

ΔS - state

ΔE - state

How does adding water to a bomb calorimeter affect heat capacity?

increases heat capacity

lower heat capacities =

higher changes in temperature